Coherent Legend-F User Manual

G

col-tEREnL

USER

LEGEND-F

MANUAL

MULTI-KILOHERTZ PULSED Tr:SAPPHIRE AMPLIFIER

WITH

•

PU

LSE STRETCHER AND COMPRESSOR

•

Copyright

Preface

Copyright United States Copyright Act form or by any means, or stored Coherent. Under the law, copying includes translation into another language.

Disclaimer

This manual provides information regarding the operation and maintenance

Every effort has been made to ensure that the infonnation document is subject to change without notice. Coherent makes no representation or warranty, either express or

implied with respect to this document. In no event will Coherent be liable for any direct, indirect, special,

incidental or consequential damages resulting from any defects in this documentation.

Coherent personnel will install the laser system. We do not guarantee laser performance unless the lase r is in

stall

Support Needs

lfyou

of

ed

by Coherent personnel

have any technical questions

Coherent

5100 Patrick Henry Drive Santa Clara, CA 95054

1976, no part

in

a database

or

by an authorized representative

or

of

this publication may be reproduced or distributed

or

retrieval system, without the prior written permission

in

this manual is accurate. All information in this

of

Coherent.

problems, please contact Coherent:

of

the Coherent Legend-F.

in

any

of

Tel: 408.764.4000 Fax: 408.764.4800 [email protected]

Manual: Version 1.0

Printed:

June 26, 2006

CcoHEREnT

.

Specifications

Legend-F Titanium Sapphire Regenerative Amplifier System

INPUT

from the Mode-Locked Ti:Sapphire laser (Mira)

Power >

Wavelength

Energy

Pulse

Beam Diameter 2-3mm

Polarization

Collimating Telescope

OUTPUT

Pulse Duration (FWHM)2 < 130fs (femtosecond version)

Pulse Broadening <150%

REQUIREMENTS:

400mW

750 - 950nm (requires cotTect optics)

Stability <10% RMS

Length <

CHARACTERISTICS:

IOOf

s (femtosecond version)

-.:

2ps (picosecond version)

Linear, vertical

1:1

<2ps (picosecond version)

of

the input duration

1

Energy (at I kHz) lmJ (after compression, Fe mto and

Energy (at 5kHz)

Beam Diameter 6-8 mm (nominal)

Energy

Polarization Linear, horizontal

1

Specifications subject to change without notice. Specifications on purchase order supercede all other

published specifications.

2

For sech2 temporally shaped input pulse only.

Stability(

±% p/p) <3%

:.-

0.31

(after compression)

Pico)

C'coHEREnl:.

--'

I

Table

1

Laser

Safety

........................................................................................................................................ 1

..

1.1 Hazards

1.2 Optical .3

Electrical Safety Precautions ........... ........ ................................................................................. 2

1

1.4 Interaction Frotn Other Lasers ................................................. .... ............................................. 3

1.4.1 Mode-Locked Laser .................................................................................. ................... 3

1.4.2 Nd:YLF Laser ............................................................................ .................................. 3

1.5

Protective Eye Wear ............................... .................................................................................. 3

1.6 Controls ........................................................

1.7 CDRH Compliance .............. ..................................................................................................... 3

Sources

1.8

System

2

2.1 Unpacking and Installation ....................................................................................................... 7

2.2

2.3 Daily

2.4

Stretcher

3

3.1

3.2 Checking Alignment/Setup

3.3 Checking the Setup

3.4 Spatial Chirp Free Alignment. .......................................... ...................................................... 17

4 Regen Alignment

4.1 Regen. Aligmnent .......................................................................................................... .........

4.2 Spectral lmprovetnent ............... ......................... .................................................................... 28

5

Optim

5.3 Third Procedure for Checking Seed Alignment to

Start-Up

Start-Up Procedure ..................................................................................................... .............. 7

Shut-Down Procedure ............................................. ................................................................. 8

Stretcher Alignment Check ......................... ................................ .............................................. 9

3.4.1

3 .4.2 Spatial-Chirp-Free Setup Procedure .............. .... ........................................................

4.2.1 Ensuring Modulation Free,

4.2.2 Ensuring correct orientation

4.2.3 Observing the Regen spectrum after seeding the Regen cavity .................................

izing Seed Alignment ............................................................................................................. 33

5.1

First Procedure to Optimize Seed Beam into

Second Procedure

5.2

5.4 Cavity Dumping a Pulse ..................................................................... .................................... 36

............................................................... ...................

Safety Precautions ....................................................................................................... I

.....

............................................................... ........ 3

of

Additional1nforrnation ...................................... ..................................................... 5

and

Shut-Down

Performance Optimization ........................... .................... .......................... ..................... 8

Alignment

Procedure

of

Preparation and Setup

Procedure

to

...................................................................................................... 7

......................................................................................................... 9

of

the Stretcher Block ............................................... ..................

the Large Reflective Gold

ofthe

Spectrometer .................................................. ..............

............................................................................................................

"f

ree-running" Spectrwn ................................................ 28

of'!!

waveplate and '!!wave voltage ............................. 29

Optimize Seed Beam into

Minor.

RA

Cavity ........................................................ 33

RA

Cavity .................................. ................. 34

RA

of

Contents

.. ..

.............................. ............... 1

....................................................

cavity ................................................ 35

II

..

14

17 19

21

30

6

Compressor

7

Replacement

Customer

8

8.1

8.2 Return

Alignment

Parts

Service .............................................................................................................................. 45

Warranty ..................................................................................... ................. ........................... 45

of

Procedures

............................................................................................................................ 43

the Instrument for Repair ........................................................................................ 45

................................................................................................ 37

C

COHEREnT

..

Warning Conventions

The following warnings are used throughout this manual to draw attention to situations or procedures that require extra attention. They warn and exceptional circumstances.

Danger!

&

Warning!

of

hazards to your health, damage to equipment, sensitive procedures,

Warning Conventions

Possible injury or hazard to personal safety

Possible damage to equipment

Caution!

Note

Eyewear Required

•

J

•

~

·

··-··

Warns against

Exceptional circumstances

Laser radiation present

Safety eyewear required

or

prevents poor performance or error

or

special reference

C'

COHEREnT

.

1 Laser Safety

This user information is in compliance with section I 040.10

Warning! t

1.1

Hazards associated with lasers generally fall into the following categorie

Hazards

• Exposure

•

Ex

of

• Electrical hazards generated

• Secondary hazards s uch as:

to

laser radiation wh ich may result

posure to chemical hazards such as particulate matter or gaseous substances releas las

er

materia l processing or a by-product

the CDRH Performance Standards for Las

of

Health and Safety Act or

performance

may result in hazardous radiation exposure.

Use

of

controls or adjustments or performance other than those specified herein radiation exposure.

in

the laser power supply or associated circuits.

of

1968. Use

procedures other than those specified herein,

in

damage to the eyes

of

the lasing process itse l

of

ma

y result

er

Products from the

controls

s:

or

of

in haza

or

skin.

f.

of

adjustments,

procedures

rdous

ed

as a result

• X-radiation from faulty power supplies

• Pressuriz

• Pressurized liquids and gasses.

ed

1.2 Optical Safety Precautions

The special nature

The safety precautions

times, ensure that a unnecessary exposure to laser radiation exceeding the accessible emission limits Standards for Laser Product

The

following precautions are to observed at all time

• Wear protective eyewear at all time radiation, the conditions

of laser lig

li

ll

personnel who operate, maintain or service the laser are protected from accidental or

lamps, hoses, cylinders, etc.

ht

poses safety hazards not associated with light from conventional sources.

sted below are to be read and observed by anyone working with the laser. At all

li

sted

in

' Performance

s,'

United States Code

of

use, and the visual function required. Protective eyewear vendors are

C'

of

Federal Regulations, 2 1 CFR I 040 I

s:

s;

selection de pends on the wavelength and intensity of the

COHEREnT

.

0(

d).

2 CHAPTER 1

listed

in

the Laser Focus World, Lasers

Consult the

ANSI, ACGIH,

and

Optronics, and Photonics Spectra buyer's guides.

or

OSHA standards listed at the end

of

this section for guidance.

• A void wearing jewelry

• Work

• Never look directly into the laser beam.

• A void looking at the beam; even diffuse reflections are hazardous.

• Use an infrared detector

• Work with the lowest beam intensity consistent with the application.

• Operate lasers only

• Limit access to the laser system only to qualified personnel who are essential to its operation and

• Provide enclosures for beam paths whenever possible.

• Terminate the laser beam with an appropriate energy-absorbing target.

• Shield unnecessary reflections and scattered laser radiation.

• Avoid blocking the output beam or any reflections with any part

• Set up the laser so that the beam height is either well above or well below eye level

in

high ambient illumination. This keeps the

of

possibility

laser.

warning signs, clearly visible to all.

who have been trained completely and made off-limits to unauthorized personnel.

eye damage.

or

other objects that may reflect or scatter the beam while using the laser.

eye's

pupil constricted, thus reducing the

to

ascertain whether the laser beam is on

in

well-marked areas with controlled access. Be sure to post appropriate

in

the principles

of

safety. When not in use, lasers should be shut down

or

off

before working on the

ofyour

body.

1.3 Electrical Safety Precautions

The following precautions should be observed electrical circuitry:

• Disconnect main power lines before working on any electrical equipment when it for the equipment to be operating.

• Do not short or ground the power supply output. Protection against possible hazards requires

of

proper connection Check these connections at the time

• Never work on electrical equipment unless there operation and hazards

• When possible, keep one hand away from the equipment to reduce the danger through the body

• Always use approved, insulated tools when working on equipment.

• Special measurement techniques are required for this system. A technician who has a complete

understanding

the ground terminal on the power cable, and an adequate external ground.

of

the equipment, and who

if

a live circuit is touched accidentally.

of

the system operation and associated electronics must select ground references.

by

anyone when working with potentially hazardous

of

installation, and periodically thereafter.

is

another person nearby who is familiar with the

is

competent to administer first aid.

of

is

not necessary

current flowing

CcoHEREnT

..

1.4 Interaction From Other Lasers

1.4.1 Mode-Locked Laser

LASER SAFETY 3

The Legend-Fuses a cw mode-locked laser as a seed beam source. The beam from the hazardou

s.

Refer to the Operator's manual provided with this laser for additional safety inf01mation.

cw

laser is

1.4.2 Nd:YLF Laser

The Legend-Fuses a pulsed, frequency doubled Nd:YLF laser as a pwnp source. The beam from the pulsed Nd:YLF laser is hazardous. Refer to the Operator's manual provided with this laser for additional safety

informat ion.

1.5 Protective Eye Wear

It

is recommended that laser-safe eye wear attenuated to the wavelength nanometers with an optical density Legend-F laser is operat exposed directly Consequently optical attenuation

it

is recommended that the eye wear selected for use with the Legend-F should also provide

in

g. Although during normal operation

to

diode laser emission, hazardous diod e radiation is prese

of

OD

7 or high

(OD)

of7

or higher at each waveleng

of

er

at the diode emission wavelength

of 1047 th

the laser, the operator should not be

of

nanometers and 523.5

be worn at all times when th e

nt

in

the laser diode pump head.

(797±2) nm.

1.6 Controls

Any modification or use

eering controls and safety features invalidates the Class IV certification

engin

manual. 'CDRH Compliance'.

The

safety featur

of the Legend-F laser which changes, disables,

es

incorporated in the Legend-Fare described bel

1.7 CDRH Compliance

The output powers and energies incorporated

I 040.1

in

the Legend -F conform to Federal performance standard as required by

O(h)(J

)(iv):

Key Switch

A separate key switch is provided to enable power to the laser. The key cannot be

removed from the switch except in the unauthorized or unqua

Protective

An internal cover is installed to cover the laser beam path unt

Housings

of

the Legend-F laser are hazardous. The following safety features

O

FF

position. This assures that use

li

fied personnel can be prevented.

CcoHEREnT

or

overrides the function

of

the laser described in this

ow

in the section entitl

of

il

it exits the optical cavity

.

21

CFR

the laser by

of

ed

the

4 CHAPTER I

at the front (output) port. The diode-pumped head is also contained within its own internal housing to shield the user from stray diode light and exposure with the internal covers removed, or displaced, except when necessary during required service functions such as optical realignment. In particular, removal head cover will invalidate your warranty.

Remote Interlock Connector

The remote interlock connector (marked 'INTERLOCK') at the rear cabinet enables the user

laser room, for example). This interlock circuit should be used to terminate laser action automatica switch

off

the external interlock circuit contacts and then cycling the key switch to clear the

interlock function. The laser should is in use.

Emission Indicators

Three emission warning indicators are used on the Legend-F laser. After the user presses and holds the laser remote control box flashes to warn personnel that the laser is about to emit laser

indicator light on the front

laser diodes. This warns the user that the user may be exposed

emission inside the laser, even though the laser cavity may not be emitting green or

infrared laser light. A third indicator light on the front

laser

is

activated and the intracavity shutter emit laser radiation. All emission indictors remain on as along as the laser is capable lasing. The indicators light several seconds prior personnel time to avoid exposure to laser radiation.

to

protect the laser diodes from

to

dust and electrostatic discharge. The Legend-F laser should not be operated

of

the diode pump

of

the power supply

to

connect an external interlock (such as a switch on the door to a

lly if

anyone enters the laser operating area. This function causes the diodes to

when the interlock contacts are opened. Lasing can only be resumed by closing

NOT

be operated unless the remote interlock function

'ON'

button on the remote control box, an LED indicator on the

li

ght.

of

the laser bench also lights any time current is supplied to the

to

hazardous laser diode

of

the laser bench lights when the

is

opened. This warns that the laser is about to

of

to

actual emission to give nearby

An

Beam Safety

A solenoid-actuated safety shutter when necessary. remote control box.

Shutter

The

shutter

is

mounted in the optical cavity to interrupt laser action

is

actuated when the laser

'ON'

button

is

activated on the

Beam Attenuator (Output Port)

A manually operated shutter mounted the beam

Location

Controls for operation operators need not be exposed to laser radiation during operation

Warning

Certification and warning labels are affixed to the Legend-F laser to with warn the user against accidental exposure to laser radiation. The location and type warning logotype labels used on the Legend-F laser power supply and bench are shown Figure 2.1

21

if

required.

Of

Controls

of

the Legend-F laser are located on the remote control box so that

Labels

CFR

1040, to provide inf01mation on the wavelength and power emitted, and

on

the laser output port is provided for blocking

C

COHEREnT

..

of

the laser.

verifY

compliance

of

to

in

LAS

ER

Operating Instructi ons

This manual contains instructions for operating and maintaining the Legend-F laser safely.

SAFETY 5

1.8 Sources

The following are some sources for add itional and training.

of

Addifional Information

1.8.1 Laser Safety Standards

SAFE

USE

OF

A

MERICAN

NATIONAL

(ANSI)

1430

BROADWAY

NEW

YORK,

TEL:

(2 1

2)

354-3300

A

GUIDE

AMERICAN

FOR CONTROL

CONFERENCE

AND INDUSTR

6500

GLENWAY

CINCINNAT TEL:

I,

(513) 661-7881

LASERS

NY 10018

IAL

OH

(Z

l36.1)

STANDARDS INSTITUTE

OF LASER HAZA

OF

GOVERNMENTAL

HYGIENISTS

AVENUE,

(ACGIH)

BLD

G.

D-7

45211

inf

ormation

RDS

on

laser safety standards and safety equipment

OCCUPATIONAL S

ADMINISTRATION

DEPARTMENT

U.S.

200

CONSTITUTION

WASHINGTON,

LASER

SAFETY

LA

SER INSTITUTE

12424

RESEARCH

AFETY

AND

(OSHA)

OF

LABOR

AVENUE

DC

20210

GUIDE

OF

AMERICA

PARKWAY, SUI

HEALTH

N.W

130

ORLANDO TEL:

, FL 32826

(407) 380-1553

.

TE

1.8.2 Equipment and Training

LASER

ONE TECHNOLOGY PARK DRIV

TEL:

FOCUS

LA

SER

P.O.

Box989

WESTFORD,

BUYER'S

FOCUS

MA

(508) 692-0700

LA

SERS

AND

0PTRONJCS

LASERS 301

P.O.

AND

OPTRONICS

GIBRALTAR

Box

650

MORRIS PLAINS

TEL:

(21 0) 292-5100

GUIDE

WORLD

01886-9938

BUYER'S

DR.

, NJ 07950-0650

E

GUIDE

CcoHEREnT

PH

OTONICS SPECTRA

PHOTONICS

BERKSHIRE PITTSFIELD,

TEL:

(413)499

SPECTRA COMMON

MA 01202-49

..

-0514

BUYER'S

49

GUIDE

7

2 System Start-Up and Shut-Down

2.1

Your Legend-F was packed with great care, and its container was inspected prior to shipment. Upon receiving your system, inspect the outside

(holes when you unpack the contents.

Keep occurred as a result de

The Legend-F can now be moved to the location

Unpacking and Installation

of

the containers immediately. If there

in

the containers, water damage, crushing, etc.) insist that a representative

the

shipping

signed container wi

Warning! •

crates

. If you file a damage claim, you may ne

of

sh ipping.

ll

assure adequate protection.

If

you need to return the system for service at a later date, the specially

in

which it will be installed.

Do not attempt to install the laser yourself, or remove the lid covering the o unauthorized, will void your warranty, and you wi for the repair yours

elf

pt

ical cavity

of

any damage incurred

.

of the laser head. Either action,

is

any maj

of

the carrier be present

ed

them to de monstrate that the damage

ll

if

you attempt installation

be

charged

or

damage

if

2.2 Start-Up Procedure

I. Turn on the external city water supply.

2. Turn on the system chiller.

3. Turn on the Millennia laser and initiate the start-up procedure as describ manual.

Ensure that the unit is operating under the standard performance specification as stated by Coherent.

4. Remove the Legend-F externa

5. Turn on the pump laser as described

6. Override the mechanical shutter (closes beam to propagate to the T i:Sapphire rod in the

l,

black Plexiglass covers.

in

the "Pump laser manual"

in

absence

Regen cavity.

C'

COHEREnT

ed

in the Seed Oscillator

of

the top covers) that allows the 527nm pump

.

8

CHAPTER2

7. Ensure "enable on" switch that provides the trigger signal

the front panel

8.

Power up the Synchronization Delay Generator (SDG) by toggling the switch located behind the SDG

unit to the

of

the SDG,

"I"

position.

is

disabled (downward position).

to

the Pockels cell drivers, located on

2.3 Daily Performance Optimization

Following parameters are check points that should

is

the entire system

I.

Fo

llowing sufficient warm-up time, ensure Seed Oscillator

within system specification. Typical oscillator bandwidth should be 35nm centered at

2. Ensure good performance from the Pump laser pump source i.e.: power and stability.

3. Ensure Regen amplifier performance.

4. Good seed alignment

well optimized as a whole.

of

the seed source into the Regen amplifier.

be

followed on a day to day basis

is

well Mode-locked and performing

2.4 Shut-Down Procedure

in

order

to

ensure that

800nm.

I. Disable the trigger signal to the Pockels cell drivers by switching the toggle switch, located on the

front panel

Power down the Synchronization Delay Generator (SDG)

2. the

SDG

3.

Tum

Power down the Seed Oscillator lasers as described in the Seed Oscillator manual.

4.

5.

Tum

6.

Tum

7.

If

not

of

the SDG, to the downward position.

by

toggling t

unit to the "0" position.

"off

' the Pump la

"off'

the system chiller.

"off'

the external city water supply.

in

place already, replace the Legend-F black, external Plexiglas covers

ser

pump laser as described in the Pump laser manual.

he

switch located behind

back

onto the unit.

C

COHEREnT

..

9

3 Stretcher Alignment Procedure

--------

The layo three main parts.

The

seco compressor, which consists main parts will

3.1

----------

ut

of the Legend-F Sub-30 fs T i:Sapphire

The

first part is the stretcher including the components from # 8 to #

nd

part is the regen amplifier, which is

be

discussed in details in the following chapters.

Stretcher Alignment Check

~--~--------~

35

36

Fig. 3.1 Legend-F

the components from # 15

of

the

components from

8

¥

37

layout

Amp

li fier is shown in Fig. 3. 1.

#32

to #34.

The

10

-

~

,:

~

14

The

system consists

11

to

#25, a nd the la

alignment procedure

})

---G-'1.

3

1

3;,-:--0.

34

28 29

of

(see al

so

Fig. 3 .2).

st

part

is the

of

the

se

three

Fi

g.

3.2 T

he

photo

of

C'caHEREnT.

the

stretcher.

10 CHAPTER3

Warning! t

5. Disable the High Speed Drivers from firing front panel

6.

Toggle the mechanical shutter switch located on the front panel the

"off"

7.

Set the wavelength Mode locking

8.

Depress the mode-Jock enable button

9. Momentarily close and open mechanical shutter to the Millennia laser

Oscillator to loose mode-lock.

I

0. Collapse fully reference iris #2 and #4 located on both sides

II.

Using an Infared viewer, ensure that the Seed Oscillator output beam is propagating simutaneously through the center external routing mirror mount located at the output

of

the Synchronization Delay Generator,

position di sabling any laser light from emitting from within the laser cavity.

is

When handling the Stertcher/Compressor grating block, always use finger cots touching any part

of

the Seed Oscillator at or near the peak (i.e. center

not necessary at this time.

of

the two collapsed irises. I

in

order to minimize the chance

of

the grating surfaces.

by

toggling the "Output Enable" switch located on the

to

the downward position.

of

the Faraday Isolator (comp. #3).

fit

is

not, one will need to steer the beam using the

of

the Seed Oscillator and mirror #

of

the Pump laser remote box to

if

accidently

wavelength@-

step a fail s to cause Seed

800nm).

I.

12. Make vertical and horizontal adjustments propagating directly through the center

of

both the X and Y axis

13. Continue going back and forth between the two mirror mounts mentioned above, while making the necassary X simutaneously.

14.

Open completely iris 2 and 4.

15

. Wearing finger cots and taking great care not to touch the grating surface. Use a 3/ 16 ba

carefully unscrew the two stretcher block (#8) as shown in the following picture.

16.

Place the subplate housing the grating in a safe and secure location.

Place the removable reference iris into the post holder situated directly in front

17. vertical retro mount #7. Collase the iris fully and make sure that the iris apearture in-coming Seed Oscillator beam.

18

. The beam height following the two 45 degree dielectric mirrors should be at 3.5". Using an infared

viewer, check to see that the Seed Oscillator beam removable mirror/mount (#5) so that the beam is through the center

andY

iri

s.

If

mirror # I so that the beam

adjustments until the beam

lf4

-20 screws that secure the top sub-plate to the rotation stage

it

is

not, make the necassry X and/ or Y adjustments

to

the external mirror mount so that the beam

of

iris #2. Conversly, make the necassry adjustments to

is

propagagting through the center

is

through the center

is

propagating directly through the center

of

the aperature.

of

the two aperatures

of

to

the 45 degree

is

of

the stretcher

is

square to the

clearly

iris #4.

ll

driver to

of

the

of

the

19. Move the removable iris into the second iris post hold of

the square 1

"x

1" turning mirror #30. The Seed Oscillator beam should again be propagating

C

COHEREnT

er

at location #3 1, situated directly

..

in

front

STRETCHER

ALIGNMENT

11

directly throu 45 degree mirror/mount #6 until

directly through the iris center when the iris is situated at both positions.

20. Once the above conditon is acompp1ished, place the removable iris back into the iris post holder at location 7. Ensure that the iris open

2 1. Momentarily close the mechan ical shutter located on the seed input panel.

22. Using finger cots, place the stretcher garting bl Re-secure the subplate by screwing the two

gh

the center

ofthe

removable iris.

it

If

it is not, make the necessary adjustments to the

is. Iterate between steps 9-11 until the beam is propagating

ing is

again square to the in-coming beam and fully collapsed.

ock

back onto the rotation stage

\/.t-20

screws

back

to the rotation stage.

of

the assemb ly.

3.2 Checking Alignment/Setup of the Stretcher Block

Wh

Warning! "

1.

Open the mechanical shutter, allowing the Tsuanmi beam to propagate into the Legend-F .

2. U

nl

ock

the rotation stage set screw l

en handling the Stertcher/Compressor grating block, always

ger

cots

in

use fin touching any part

ocated

order to minimize the chance

of

the grating surfaces.

at the base

of

the grating assembly as s hown in Fig. 3.3.

of

accidently

3.

Using an infared viewer

of

surface towards the iris at l

the stretcher grating appears to

Fig. 3.3 Rotation set screw indicated

ocat

or

an IR card, rotate the upper portion

be

retro reflecting the Seed Oscillator beam

ion 7. See

gra

ting orientation shown below in Fig.3.4

by

of

the grating stage so that the

arrow as shown above

back

CcoHEREnT

..

12

CHAPTER3

Fig. 3.4 Stretcher grating alignment for

4. At this time it is that the retro reflection coming as it is going into the stretcher assembly.

Once the zero order surface reflection necessary adjustment place the zero order reflection where it

If

the zero order reflection appears to be

adjustemnt

Unlock the rotation set screw.

5.

6. Rotate the grating assembly clockwi grating to be propagating back to the iris at location

7. Lock the rotation set screw once the reflection be at the sa (see Fig. 3.5) behind the mirror mount

mount. min·or mount aperature. With one hand, rotate the grating/holder so that the first order retro reflection appears

is

not important that the retro reflection is exactly through the iris .What is important

off

the grating

is

at or near the iris, relock the rotation set screw. Make the

to

the "fine" rotation adjustment screw located on the rotation stage as to

is

off

to

the vertical axis

me

height as the iris center, loosen the two 3/32 screws that contain the retainer rings

Using a 1/

16

ball driver, loosen slightly the set screw holding the grating holder within the

to

be propagating back to the iris center beam height .

of

the mirror mount holding the stretcher grating.

se

while looking for the first order reflection from the stretcher

just

the

zero

order

surface reflection.

is

propagating back to the iris at the same height

visible near the iris.

in

height (3.5"), using a 1/8 balldriver make an

7.

is

near the iris.

enough to allow coarse rotation

If

the retro reflection appears not to

of

the entire grating

•

COHEREnT

.

STRETCH

ER

ALIGNMENT

13

1

8

3 2

7

Fig. 3.5 Two 3/32 screws grating rotation in the vertical plane.

8.

Unlock the rotation set screw and again rotate the entire grating assembly so that the zero order retro reflection see that the grating refl ection is sti

ve

rtical adjustment to the mirror mount.

9. Unlock the rotation set screw and rotate the grating b lock so that the first order reflection is aga near the iris. Check to see that it is s till at the same height as the ir

0. Iterate between step 3 and 7 unti I both the zero and first ord

I

grati

ng surf

11

. Once the zero and fi rst order reflections appear to be at the same height, tighten both the I /6 set

screw and

ofthe

height reioosen the screws and attempt prior to tightening the the screw.

that

lock the retain rings behind

is

aga

in

visible near the aperature

ll

at the same height as the iris. If it is not, then again make a

ace at the same height as the iris center.

th

e two 3/32 balldriver screws. Check to

two order reflections has not changed relative to the iris center. If one or both has,

to

compensate by off-setting the height that the beams propagate

the

mirror

of

the iris. Lock the set screw. Again check to

see

that after both have been tightened, that the

mount

are

used to

is

center.

If

it not, re-do step 5.

er

reflections are propagating

adjust

off

the

in

the

C

COHEREnT

..

14

CHAPTER3

3.3 Checking the Setup

I. Using an infared viewer, rotate the grating assembly so that the first order reflection

stretcher grating appears to be stricking the center (horizontally)

2. Using the viewer, observe the stretcher grating surface. With the removable iri s still located directly the grating surface. See Fig. 3.6.

in

front

Stretcher

of

the vertical retro reflector, one should see two spots located near the center

g•·ating

of

the Large Reflective Gold Mirror

of

the large gold reflective mirror.

0

Fig. 3.6 from

The

top

the

retro-retlection

spot

is

the

mirror

seeding

behind

beam

from Seed Oscillator.

the

stretcher

grating.

The

second

spot

is

the

of

beam

the

of

reflected

3.

If

the iris were not in place and the setup

vertically over one another. Each spot representing one pass within the stretcher setup as shown in

Fig. 3.7.

Stretcher

grating

Fig. 3. 7

Four

of

the stretcher was ok, one would see 4 spots lined

•

thirdpass

.inputbeam

•

spots

second

•

"stretched"

on

the

pass

stretcher

output

grating.

beam

C'

COHEREnT

.

STRETCHER

ALIG

NMENT

15

4. Tweak the vertical micrometer adjustment knob (Fig. 3.8) located behind the large gold

Fig

mount clockwise until the surface reflection from the lar condition as shown above.

..

3.8

This

picture

In making the above adjustment, the purpose

a) check the setup

b) check the mechanical integrety the beam does not appear to be moving horizontally as the vertical ad

very important that it only move vertically. not

be

shows

the

vertical

of

the large gold mirror horizontally

optimized leading to potential problems recompressing.

micrometer

of

the vertical axis

If

knob

of

the procedure is to:

it

is

ge

gold mirror appears to be

for

the

6"

diameter

ofthe

lar

ge gold

not moving vertically, the stretcher setup will

gold mirrot-.

mirror mount ensureing that

ju

stment

in

is

being made.

mirror

the same

It

is

If the beam is moving horizontally while making a vertical adjustment following step 4, with the mount in place,

• check the tightness

• Ensure the mirror the top

Ensure the micrometer adjustment screw tip is lubricated us

If

after doing step 4, the beam from the large gold mirror appears to

5. up as shown

coarse adjustment by loo entire mount the amount nesassary

vertically as shown

' fine" rotation micrometer knob so that they line up vertically.

6. Readjust the vertical micrometer knob beam from the large go

the lower most part mirror (Fig. 3.9) so that it i

If

the mechanics

be stricking the above mirror at

of

the mount

in

Fig. 3.6) on the grating surface by more than

in

of

the lar

of

all the 3/

is

flat within the holder and secure via the nylon tip set screw located at

se

ning the baseplate to the large mitTor mount and physically rotating the

Fig. 3.6. lfthe two spots are

ld

mirror to go up and over the grating stage assembly ultimately stricking

the

I"

x 7" dielectric retro reflector (# I 0). Position the beam on the I" x 7"

s@

3-4mm above the bottom edge

ge

mirror mount are sound, the beam from the large gold mirror should

or

16

screws

on

the mount.

in

g, for example, Krytox grease

be

off

horizontally (not lining

Yz

a em, one will need to make a

in

order to setup the mirror so that the two spots line up

offset

to

the lar

ge

near the bottom

by less than

mitrror mount counter clockwise forcing the

of

the

mirror and centered horizontally. I

Yz

em then s imply adjust the

the mirror.

fit

is

C'

COHEREnT

..

16

CHAPTER)

not, loosen the nylon tip set holding the beam is near center (horizontally).

Fig. 3.9

7.

The

arrow

shows the

With the viewer, following the above step, observe the stretcher grating once again. Again one should see the two spots lined up vertically.

the horizontal axis

input

spot

horizontally. Tweek

lower spot is @ 3-4mm below the input spot.

of

the I" x

1" x 7"

7"

if

I" x 7"

retro-rflection

retro reflector

necessary the vertical axis

mirror and position it within the mount so that the

mirror

If

the lower spot appears to be offhorizontally, adjust

so

that t

he

behind the stretcher grating.

lower spot

of

the 1" x

is

located directly below the

7"

retro reflector

so

that the

8. Remove the "removable" iris from within the iris holder.

9.

Observe the stretcher grating surface once again. One should now see four spots lined vertically over one another as shown following step 3 above.

I

0.

If

the upper and lower spots appear to

3.1

Fig.

that

A second check point

tweak the X and/

0), adjust the horizontal axis

the upper and lower spots line up.

to

observe

is aligned correctly both in the X

or

Y -axis

of

the vertical retro reflector so that the second spot visible is super

imposed upon the main beam. When this is the case, all four spots should line

Stretcher

grating

be

off

horizontally with respect to the two inner spots (see

of

the upper mirror mount

is

at the 1

"x7"

retro mirror location.

andY-axis,

one

.third

•

of

should only see

pass

input

beam

second

pass

"stretched"

the vertical retro assembly

If

the vertical retro reflector

one

spot.

If

two spots are visible,

up

vertically.

output

beam

•

Fig. 3.10

The

misalignment

of

the

1" x 7"

reflection mirror.

so

C

COHEREnT

..

STRETCHER

11. Mode-lock the Seed Oscillator and ensure optimum performance. When this is the case, one ld

be able to observe the following pattern (Fig. 3. 11) on the grating surface.

shou "strips" appear shifted horizontally, make a slight rotation to the grating block so they appear as shown below.

ALIGNMENT

If

the two

17

Fig. 3.11

Stretcher

The

grating

optimum

performance

of

•

the

spectrum

"stretched"

3.4 Spatial Chirp Free Alignment

The stretcher setup (distance Coherent prior to shipment. However, greater than 3.5' away, the divergence going to be different from the divergence Some reoptiminzation

of

Operation

the Pwnp laser will not be necessary at this time.

of the stretcher setup may be necessary.

ofretro

reflector to large gold minor) is preset at

if

at installation, the Seed Oscillator is setup

of the beam entering the Legend-F is probably

of

input

beam

output

beam

pattern

on

the

stretcher

grating.

the Seed Oscillator used at the factory.

3.4.1 Preparation and Setup

I. Ensure that the Seed Oscillator is perfonning to system specification and well Mode-locked.

2. Ensure that the beam from the Seed Oscillator is well collimated. Reroute the beam from the Seed Oscillators present location and allow the beam

the layout Oscillator to the time the beam ent two thereafter.

3. Setup a spectrometer at the output

4. Observe the spectrum from the output

in its current operation. Typical output spectrum from the Seed Oscillator should be as smooth as

possible with no apparent modulation as shown

I

OOmm

of

the Seed Oscillator is 3 feet or more away from the time the beam exits from the Seed

broadband lenses). Install th e telescope, ensuring that the beam is well collimated

of

the Spectrometer

to

propagate 6 meters or more to the far field.

er

the Legend-F , a

of

the

Legend-For

of

the Seed Oscillator. Note the bandwidth and wavelength

in

Fig. 3.12.

l:

I telescope is recommended (for instances

somewhere appropriate on the system bench.

CcoHEREnT.

If

18

CHAPTER3

Fig. 3.12 nm

Typical

/div)

5. Remove the output panel the two support bracket

6. Place a mirror between mirror # 12 and #13 and setup an external turning mirror to direct the stretched output beam into the spectrometer as shown

7.

Setup the spectrometer to be able to monitor the spectrum from the stretcher using an oscilloscope.

Seed

Oscillator

s.

Fig. 3.13

Spectrum

of

the Legend-F by backing out the corresponding set-screws located on

peak@

Spatial-chirp-free

800nm.

Bandwidth

in

Fig. 3.13.

alignment

JO:j45nm

setup.

(calibration=

10

8. Connect a oscilloscope. Set the time base to 1 ms/div.

9.

Connect a second BNC cable to one end to the oscilloscope amplifier base. Set the amplitude

is not saturated.

I

0. Tweak the horizontal axis Observe the spectrum on the oscilloscope. spatial chirp (spatially varying spectrum). This spatial chirp minor (#1 divergence). Upon tweaking the external mirror, the signal present on the oscilloscope should not

BNC

cable from the 'Trigger out"

0) is not exactly at the actual focus

of

the spectrometer to the time base

of

the Spectrometer "signal " out. Connect the other end

of

the monitored spectrum such that the signal

of

the external mirror used to route the beam into the spectrometer.

If

the Stretcher is not setup correctly, there will be a

is

caused by the fact that the 1

of

C

COHEREnT

the large curved gold

..

minor

ofthe

(given the input

"x

7"

STRETCHER

ALI

GNMENT

19

"sweep" left

"x

7"

I

the external mirror.

or

right on the screen. If thi s is the case, one will need to optimize the distance

mirror relative to the gold mirror so that the spectrum immediately collapses when adjusting

3.4.2 Spatial-Chirp-Free Setup Procedure

1.

Ensure Seed Oscillator is well mode locked

se

2. Ensure stretcher is prematurely

3.

Reference, position. As a second reference, with the Pump laser shutter closed and the Seed Oscillator beam blocked from entering the Lege the surface

4. Loosen the 3/32 screw securing the 1" x 7" mirror that the base plate remains flat to the bench but not slide back and forth.

If

after loosening the base plate the monitored spectrum signal on the oscilloscope has changed,

5.

use an infrared viewer to observe the stretcher grating. appear to be changed verticall back monitored signal back on the osci

if

possible, the base pl ate

ofth

e large gold min·or and the s

of

the large gold min·or so that the grating alignment appears normal. This should recover the

tup following the " Stretcher alignment check" procedure.

of

the 1" x

nd-F,

using a tape measure, measure the exact distance between

y.

If

this is so, tweak the micrometer (vertical axis) located at the

ll

oscope.

urf

7"

ace

mirror mount to the breadboard

of

component #10, while

mount(#

so

I 0) to the breadboard. Loosen it such

snug such that the mount wi

The

alignment on the stretcher grating may

in

its current position.

of

in

its cun·ent

ll

not be able to

the

6. Slide

7.

8.

9.

10

. After correcting for the 'spatial chirp" in the stretcher, lock the 1" x

11. Tweak the micrometer adjustment

12. Remove the mirror placed between the min·ors #

13. Fo

in

one direction, the mount housing the 1" x

Using an infrared viewer, observe the grating surface. Ensure that the strips appear to be centered to

th

e grating aperture after each increment change.

adjusting the e ntire

After changing distance horizontal axis

The

further

or broader the monitor horizontal axis

stretcher.

breadboard, ensuring that the strips on the grating are lined up correctl

are fitted within the grating aperture without clipping

ll

ow the

pro

1" x 7" mirror mount.

by

a millimeter and optimizing for any horizontal shift, tweak the

of

the external mirror to check the spatial chirp on the oscilloscope.

closer the I" x

ed

of

the external mirror. Fig. 3.14 and 3.15 show the spectrum before and after the

cedure "optimizing the seed beam to the Regen cavity" .

7"

mirror is to the optimum distance

spectrum will appear to sweep across the scope screen when adjusting the

of

the gold mirror so that all the four passes within the stretcher

7"

mirror, by millimeter increments.

If

they are not, reposition them horizontally by

of

the actual focal length, the

7"

mirror/mount to the

y.

..

12

and #13.

C'

COHEREnT

.

20 CHAPTER 3

Fig. 3.14 Typical spectrum measured from Bandwidth= 35

3.15 Ty

Fig.

nm, calibration is 4.4 nm/ms)

pical s

pectrum

measur

ed

aft

er

Seed Oscillator.

the

str

etcher. (Ce

(Center

nter

wavelength @ 795 nm,

@795 nm. Bandwidth =

31

nm)

C

COHEREnT

.

21

4 Regen Alignment Procedure

4.1

Regen. Alignment

Handle all optics while wearing finger cots.

The following procedure explains in detail how to do an alignment

Legend-F Regen cavity only when the intracavity alignment has been grossly misaligned.

Since most optics will need

optics carefully to ensure that no other optics may have also damaged when damage to the r occurred.

If

upon inspection, some

methanol/acetone at

Materials needed:

lens tissue

Hemostats

Methano

two sheets

Vac

of

to

be

removed from their holder(s) at this time, visually inspect all

of

th

is time.

etone

polarizer sheets

the optics are found to be dirty, clean using

of

the

od

two Reference blocks with crosshair target set at

45 degree turning

I)

Using a 3/16-ball driver, remove

the mount on top

coating.

2) For reference purposes, posit ion holder.

3) Ensure that reference iris #

4) Remove Pockels cell #

Note: prior to completely removing the Pockels cell

cell so that it is replaced back in its original setup. The Pockels

of

the setscrew at the top

2.5"

minor

/mount

minor

# 15

of the regen cavity from within its mount. Place it near

of

a piece

of

lens tissue with the coated side facing upward as not to scratch the

if

not already, inscribe a mark on the white Teflon holder relative to the

of

the mount. Remove the

17

is completely ope

18

from within its holder by:

C

COHEREnT

n.

from within their mount, note the current orientation

\14

waveplate (# 16) from within its

ce

ll

windows have a slight wedge

.

so

of the

the

22 CHAPTE

R4

orientation (placement)

in

5mm

A.

B. Removing only the

either direction.

Indexing the base Unscrew the two assembly and place away from the cavity as allowed by the cable lengths.

a) Ensure SDG

off.

b)

Un-plug the l20vac plug leading from the SDG to the input panel

c) Using a 3/32 balldriver, remove the four screws located on top

voltage cover.

Using a 8/32-socket head driver, remove the two hex nut screws securing the High

d) Speed Driver High Voltage leads

e)

Using the 3/32 ball driver loosen the support bracket(s) that secures the cell within the

mount.

f) Remove the cell from within the mount and place in secure location away from the

Regen cavity.

of

the Pockets cell will deviate the beam passing through the cell horizontally by

of

the Pockels cell mount

V4-20

screws securing the mount

Pockels cell from within mount. Follow

is

turned

off

. High voltage present at Pockels cell leads

in

their current position as to maintain a reference.

to

the breadboard and remove the entire

to

the Sol Gel Pockels cell.

"a-f'

if

unit not turned

of

the Legend-

of

the Pockels cell High

F.

5) Remove the zero degree turning mirror (#19) that folds the Regen cavity from within its mount. Also place at or near the mount.

6)

Remove component #

pumping the Ti:Sapphire rod

7) Remove the vertical plate of

the mount. Doing so will minimize replacement

is re-assembled upon completing the alignment

Upon removal

component #12, should now be propagating towards the side panel closest to the Regen cavity.

8) Tweak the vertical axis propagating along the tabletop at 2.5".

9) Taking a separate 45 degree mirror (dielectric broadband, gold or silver coated)/mount. Position it such that the beam from the panel, towards the output end

of

41

that serv

the vertical plate, the output

of

es

as the beam dump used to dump the residual 527nm beam after

of

component #

mirror # 12 so that the beam coming out

I

"x

1" square mirror

of

the Legend-F as shown

13

by

unscrewing the two 8/32 screws located at the base

of

the vertical plate once the polarization rotator

of

the Regen cavity.

of

the stretcher beam, as it takes a 90 degree tum

off

the 1

"x

1" square mirror

is

turned 90 degrees, propagating along side the

in

Fig . .4.1.

off

of

is

C

COHEREnT

.

RE

GEN

ALIGNMENT 23

14

Note: conveniently, one can use mirror/mount # tw11in

g miiTor for optically aligning alignment source. 1f on e chooses this component as the second alignment mitTor/mount, flip the mount 90 degrees upon its base plate and at the same time rotate the variable base plate so that the round

va

ri

able locking ring is located dir

Repo sition component # 14 behind the Regen cavity as shown on the following diagra

of

the Regen cavity using the stretched output beam as the

ect

ly

in

front

to serve as the component for use as the second

of

where the actual mirror is located within the mount.

m.

5

~

J-lo-~---

Fig.

4.1

Use

1 0) Set a block with a cross pattern at exactly 2 .5" above the Legend-F (serves as a reference target)

breadboard cross pattern centered directly to the hole center.

11

) Without permanently locking component #

mirror moun propagating parallel

Use the reference block mentioned above as the

1

mirror

dir

ectly on top

t#

14

in

>..

36

37

#14 as a turning

of

its new location such that the intercepted stretched output beam appears to be

to

the Regen si

12

7{--':::::'3:

13

39

14

mirror

the last hole

de

panel along hole pattern #2

l ---\

7,_

~------

for

the

pre-alignment

of

row #2. Place the block with its bottom line

14

to the breadboard, in a coarse manner, maneuver

far field reference target.

./~

-

~

of

the regen cavit

the Legend-F bench .

31

J(J

35

y.

of

the

in

12) Us

1

14)

15)

16)

17) Continue steps I

g a second reference block, p lace the cross hair target directly on top

#

2)

closest to component # 14. Observe where the beam is relative to the cross pattern. Move the

mount according

3)

Remove the block.

Once the position

using a 3/32 screw, lock component #

Once the mount is secured to the tabletop, observe where the beam is r

hair on the mount l the cross mirror/mount #14 so that it is.

Place the second reference block

hole referred to in step I not centered to the cross hair target, make the

l"xl" mirror/mount #12 so tha t it is

along row #2

ha

to

the

dir

ection the beam needs to go relative to the cross pattern.

of

the mount is such that the beam is close to the referenced holes along

14

to the bench so that it is secure.

oca

ted towards the output panel

ir target center. 1f it is not, make the necessa1y adjustments

(or

relocate the block nearest the output panel) directly on top the

0. Observe where the beam is relative to the center

0-12 unt

of

the breadboard.

il

the beam is perfectly centered to the crosshair patterns at both locations

CcoHEREnT

necess

of

the Legend-F. The beam should be sticking

my

adjustments to the X a

.

of

the hole (hole pattern

row

ela

tive to the reference cross

to

the X and Y -axis

of

the cross hair.

ndY

-axis

of

If

the

#2,

it is

24

CHAPTER4

18) Position the mirror mount #

15

(if

necessary) so that the " exposed" mirror aperture

of

the mount is

centered to the in-coming "stretched" beam.

19)

Place the

waveplate center. cock the mount

!14

waveplate back into its holder. Ensure that the beam is propagating directly through the

If

it

is

not, loosen the base plate and reposition the mount so that it

off

horizontally so that there are no surface reflections from the waveplate

is.

Slightly

propagating back towards the Stretcher setup.

20) Again, remove the waveplate from within its holder.

18

21) Close reference iris # should be perfectly collapsing upon the propagating beam . both

in

the X

andY-axis

Place Pockels cell #17 back into

22)

completely. Observe where the beam is relative to the iris center.

If

it

is

not, mechanically adjust the iris

so that it is.

it's

mount, in the original orientation that the cell was in prior to commencing the cavity alignment. Resecure the cell back into its holder following the reverse order as stated

in

step 4A-a-f

Using a white business card, ensure that the beam is propagating directly through the center input and output apertures cell

by

loosening the two 3/32 balldriver screws securing the mount to the breadboard.

23)

Housed inside the Pockels cell

of

the Pockels cell. I

is

a KD*P crystal.

fit

appears not to be, one will need to relocate the

It

will be necessary to align the optical axis KD*P crystal along the propagating beam. The cell will need to be tilted about two axes to achieve this. (see Fig. 4.2).

The

of

iris

both

of

the

Fig. 4.2 Adjustment for the Pockels cell

24) Place a white business card mid way between component #

25)

Place two pieces

of

cross-polarizing film directly

Pockels cell

26) Place a piece

of

lens tissue between the input aperture scatter the beam through the cell. Using an infrared viewer, observe the pattern on the white business card.

One should see a pattern as the one shown

TOP VIEW

in

Fig. 4.3.

SIDE VIEW

19

and # 17.

in

front

of

both input and output apertures

of

the cell and the polarizer sheet

in

of

the

order

to

REGEN ALIGNMENT

25

Fig. 4.3 Scattered aligned correctly.

27) If the observed pattern does n Y -axis adjustments.

pattern

of

the Pockels cell mount will be needed (See Fig. 4.4). Use a

Vertical adi .

0

-

D

~

CJO

after

the Pockels cell sandwiched between two cross-polarizer if it

ot

appear to look like the pattern above, an adjustment to the X and/or

118-ba

ll

driver

to

make the

is

Hor

izontal

Fig. 4.4 The adjustment

28) Remove two-polarizer sheets and the lens tissue from around the Pockels cell apertures.

29) Remove the white business card from within the beam path allow mirror #19.

30) Reinstall the zero degree ball driver.

31) Index the Ti:Sapphire rod mount to its present positi

32

32) Using a 3/ out and away from

Pla

ce

33) that the beam coming from folding mirror # 19 is propagating para above. If it

34)

Place the Ti:Sapphire rod /mount back into its indexed position.

balldriver, loosen the two screws securing the mount to the bench. Remove and place

the reference blo

is

not, tweak the vertical adjustment

mitTOr

it

s current position.

ck

with the cross hair target directly in front

of X andY

back into its holder. Secure within its mount using the 1/ 16

C'

COHEREnT

axis

of

the

Pocke~.-

on

on the breadboard.

ofthe

zero degree mirror #

.

____

in

g the beam to propagate towards

of

component #21. Check to see

ll

el

to

the bench top at

_.J

19

so that it is.

2.5"

26

CJ

!APTER 4

ofthe

35) Assuming the angle tissue directly in front

Place a reference block with a white business card tapped or leaning against the block 2-3 inches

36) away, located on the other side

37)

Using an infrared viewer, observe the pattern created by the lens tissue. One should be able to see

the rod aperture relative beam does not appear to be centered, tweak the horizontal adjustment

38) Remove the reference block from within the Regen beam path following the rod.

Ti:Sapphire rod

of

rod side facing component# 19.

of

the rod.

to

the beam propagating through the rod (in this case scattered).

is

correct

in

its present location, place a piece

of

mirror#

of

lens

If

the

19 so that it is.

39) Remove the lens tissue

40) After the beam has propagated through the rod, the beam should strike the inside edge

second zero degree mirror (component #21), at this time the beam will fold back propagating

towards the output panel.

41) At this time, remove mirror #25 from within its mirror mount.

42) Remove photodiode #

Place the reference block with the crosshair target at 2.

43)

corresponding to mirror #25.

44)

If

the beam from mirror #

adjustment

45)

Collapse fully iris #23.

beam, position the height

46)

For the horizontal axis

center

47)

At this time, using a white business card, observe the passing

dielectric polarizer (#22). The beam should be passing through the polarizer center.

infrared viewer to verify this. to the table, and slide the base plate (keeping the mount square mount vertically until the beam

of

mirror mount so that it is.

fi·om

in

front

of

the other side

The

beam should at this time be

41

from its present position.

21

is not striking the reference block at the 2.5" mark, tweak the vertical

If

upon closing the iris, the center

of

the iris so that it does so.

of

component #21, tweak

If

it does not appear to be, loosen the 3/32 screw securing the mount

is

passing through the center

ofthe

Ti:Sapphire rod.

at

2.5" above the breadboard top.

5"

so that it is located behind the mount

ofthe

iris

is

not collapsing upon the

it

so that the beam is passing through the iris

of

the beam through the broadband

to

the input/output panel)

of

the component.

of

the

Use an

of

the

48) Resecure the baseplate

49)

Following the iris, the beam should be propagating through the center ofPockels cell #24.

beam does not appear to be so, loosen the baseplate screws and slide the mount vertically so that it is.

50) Follow steps 24-26. Set the pitch and yaw (vertical and horizontal axis) two polarizer sheets/lens tissue.

Place mirror #25 back into its holder and secure by tightening the mount set screw using a 1/16

51) ball driver.

52)

Using an infrared viewer, observe collapsed iris #23. Look for the retro reflection to be propagating

from the surface through the iris center, adjust the vertical and horizontal axis

to

of

mirror #25 back to the collapsed iris.

the bench.

C'

COHEREnT

ofPockels

If

it does not appear

of

mirror #25 so that it is.

..

cell #24 using

to

be going back

Ifthe

REGEN

ALI

GNMENT

53) Fully open iris #23 .

54) Collapse iris # 18.

Using the infrared viewer, look for the retro reflection from mirror #25 propagating back to the

55) center

of

iri

s#

18.

Make,

if

any, adju stments to component #25 so that the retro reflection has

propagated also through the iris ce nte

r.

27

56) Open fully iris #

5

7)

Insert optic #

ll

58) Co

59) Again using the infrared viewer, look for the retro reflection from mirror #

apse fully iris # 4.

through the stretcher setup towards iris #4

This completes the alignment

Pump the Regen cavity with the 527nm-pump beam from the Coherent Pump laser and refer to the procedure

18

15

back into its holder.

of

"Op

timizing the Regen cavity

of

the Faraday Isolator setup.

the Regen cavity.

".

15

propagating back

C'

COHEREnT

..

28

CHAPTER4

4.2 Spectral Improvement

1)

Block the seed from propagating into the Regen cavity. Interrupt propagation

mechanical shutter

or

by

blocking the seed into the Regen using a beam block.

by

closing the

2) Use an external turning mirror/mount, and position it between component #29 and the l "x

mirror (#30). Direct the regen output beam into the Spectrometer.

3)

Monitor the Q-switch spectrum

Fig. 4.5.

Fig. 4.5 Typical spectrum from Regen cavity

4)

The output Spectrum from the Regen should

smooth as the

Seed Oscillator output in comparison.

out

of

the Regen on the Oscilloscope.

be

as smooth as possible although it will never

It

should appear as shown

l"

square

be

as

in

ofthe

Various parameters various parameters that could potentially modulate the spectrum are:

a) Misalignment

b) Inappropriate setting

c) Incorrect

Y4

system could induce modulation across the spectrum. In the regen, the

of

the Pockels cell(s)

of

the

Y4

waveplate

wave voltage to the Pockels cells

in

the Regen

4.2.1 Ensuring Modulation Free, "free-running" Spectrum

In order absences

to

ensure that all parameters above are optimized correctly, it is best

of

some

of

the contributing parameters. To do so, do the following:

Di

sconnect the BNC output cables corresponding to "output 1 and output 2"

I.

allows the triggering

2. In its present position, using a black marker, inscribe a reference mark relative to the set-screw securing the replacement

of

the scope for monitoring the Regen (free-running) intracavity light.

Y4

wave plate holder

the wave plate to its original position when one is done.

C

COHEREnT

to

the mount. Doing so will allow

e

to

look at the spectrum in the

(if

of

the SDG. Doing so

one

is

not there already)

REGEN ALIGNMENT

29

3. Observe the free-runn ing spectrum appear as shown in the previous photo. horizontal adjustment to one

either Pockels cells is misarranged. Example

Y4

turn

of

a ball driver in the horizontal (yaw) axis can

4. Tweak the two cells individually such that the spectrum appears the least amount modulated. gross adjustments are made, it may be necessary to tweak the end mirror corresponding to the Pockels cell that has been adjusted in order to recover the optimization

on

the oscilloscope after removing the wave plat

If

the spectrum appears to be modulated, a verti cal and/or

or

both Pockels cell will need to be made depending on how severe

of

misalignment

be

seen

of

in

the Pockels ce

Fig. 4.6.

of

cavity alignment.

e.

It

should

ll

# I by less than a

If

Fig. 4.6 Pockels cell

#1

miss-alignme

nt

4.2.2 Ensuring correct orientation of% waveplate and

I) Rep lace the

mark.

2) Reconnect the B

3) Observe the

insertion slight rotations to the an example

Y4

waveplate back to its original position as dictated by the inscribed

NC

cable to "output 1" enabling the firi ng

Q-

switch spectrum on the oscilloscope. Ensure that the spectrum is not modulated after

of

the waveplate into the Regen cavity.

Y4

waveplate with emphasis

of

the Regen spectrum modulated

Ift

of

as a function

of

Pockels

he spectr

smoothing the modulated spectrum. Fi

um

appears to be modulated, make

of

slight

%wave

cell#

Y4

waveplate misalignmen

1.

voltage

bla

ck

reference

g.

4.7 is t.

Cco

HEREn

T..

30

CHAPTER4

Fig. 4.7 Q-Switch spectrum modulated as a function

4)

Tweak the potentiometer

Pockels

to

a function

tweaks to one

ce11

# l while observing the Q-switch spectrum. Again it should

of

voltage.

or

both parameters should ultimately yield a nearly modulated free spectrum.

on

the high voltage power supply(HVPS) that varies the high voltage

If

modulated, the spectrum will appear similar to the photo above. Slight

of

Y..

waveplate orientation

not

be

modulated as

4.2.3 Observing the Regen spectrum after seeding the Regen cavity

While s

ti11

observing the Q-switch spectrum (Fig. 4.8), allow the seed beam to propagate into the Regen cavity. In doing so, two things should happen; upon seeding the Regen, the center itself to the Regen spectrum.

not

spectrum does to the Regen. the bandwidth unseeded reg. spectmm. (see Fig. 4.9)

collapse upon the center

Tweak

the slit

of

the seeded spectrum

Observe this case while monitoring the oscilloscope.

of

the Regen spectrum, the Seed Oscillator wavelength is

of

the Seed Oscillator and/

is

maximized and central wavelength matched t

or

the x-axis

Seed Oscillator spectrum should

If

the seeded

ofthe

optical components #14

he

peak

ofthe

so

off

that

set

Fig. 4.8 Unseeded reg. Spectrum. (center @ 800nm. Bandwidth =33 nm)

C'

COHEREnT

.,

R

EGEN

A LIGNMENT 3 I

Fig. 4.9 Reg. spectrum

after

seeding. (center @80Snm,Bandwidth = 26 nm)

CcoHEREnT.

33

5 Optimizing Seed Alignment

5.1

First Procedure to Optimize Seed Beam into RA Cavity

1.

Following sufficient warm up time, ensure Mai Tai is well mode-locked and performed with

system specification.

2. E nsure good performance from

3. Ensure RA cavity is well optimized

RA

4. Monitor the The typical Q-Switch pulse is shown

cavity radiation using the Coherent fast photodiode situated behind mirror #25.

th

e Evolution pump source (i.e.: power and stability).

in

the absence

in

Fig. 6. I 8.

of

the seed pulse.

in

Figure 6.18 RA Cavity Q-Switch pulse

Figure 6.19 RA Cavity

C

COHEREnT

"seeded" radiation

..

34

CHAPTERS

5. Delay out the switching time to Pockels 500ns.

6. Provided that the Mai Tai

enter the Legend-F

7.

If

the alignment

greatest amount

pulse into the RA cavity

The

difference in buildup between the two conditions

seed beam should be

of of

is

optimized and well Mode-locked, allow the beam from the Mai Tai to

by

opening the mechanical shutter

the stretched output beam into the RA cavity is optimized, one should see the buildup reduction between the Q-switch signal and the seeding

(See Fig. 6.19).

"co-linear/superimposed" with the intra-cavity light

cell2

(#24) so that the SDG digital readout

of

the Mai Tai with computer.

is

typically >55ns. When this

of

the RA.

5.2 Second Procedure to Optimize Seed Beam into

1.

Ensure that Steps 1-7 above are satisfactory.

2. Momentarily toggle to the the SDG. Doing so will not provide trigger signals to the High Speed Drivers consequently disabling the RA cavity from emitting laser light.

3. Roll out the timing to

"orr•

"output

position the "

2"

such that the digital display indicates 500ns.

output

enable"

switch located on the front panel

is

of

is

RA

more than

the Mai Tai

the case, the

Cavity

of

4. Take a white card and place it directly #15).

5.

Using an infrared viewer, locate the "stretched" output beam as it strikes the card.

Switch the "

6. cell #

7. Using the IR viewer, observe where the depolarized light coming from the Ti:Sapphire rod is relative does not appear horizontal axis

8.

Move the card from

interrupting the RA intra-cavity light.

9. Again using to

where th e depolarized light coming from the Ti:Sapphire rod beam is.

10.

If

the two beams are not super imposed upon one another at this point, tweak the X and/ or Y-axis

of

mirror #

Warning! •

output

1.

to

where the beam from the stretcher is on the card.

14

enable"

to

be superimposed upon the stretched output beam, tweak the vertical and/

of

mirror #

in

theIR

viewer, observe where the "stretched' output beam is striking the card relative

so that it is.

switch back

15

so that it does.

front

of

component #

Take great care not to accidentally limit the "stretched" spectrum. T he reduced spectrum may cause the damage the optics in the RA.

in

front

of

component #14 (between components #14 and

to

the upward position enabling the firing

If

the Depolarized light from the rod

15

and place it as close to the rod as possible without

of

the Pockels

of

or

C

COHEREnT

.

SEED ALIGNMENT 35

11. Continue iterating between steps l

oca

tions.

At this time, the RA cavity should now

scope, tweak both the vertical and h

alignment.

4-10 until both beams are superimposed

be

"seeded". While observe the buildup reduction on the

or

izontal adjustments

of

mirror #

on

one another at both

14

to finalize the seed

5.3 Third Procedure for Checking Seed Alignment to

I. Ensure that the RA cavity is well optimized

cavity irises are align symmetrically collapse around the laser cavity

both the X and Y-axis. Check and repositi on the two irises one at a time but RA cavity is optimized

2. Toggle to the Doing so will not provide trigger signals to the High Speed

cavity from em itting laser

3. Collapse fully the two intra-cavity irises (#

in

4. Us

g an infrared viewer, observe the two iris apertures as the seed beam is allow ed to propagate into the RA cavity. The seed beam should be propagat the case, tweak component #

seed beam is centered to iris #23. Continue iterating between the two m irro

passing through the center simultaneously.

"off'

ed

to th

e intra-cavity light. (Upon collapsing the iris, its center should

in

both power and spatial profile.

positi

on

the "output enable" switch located on the front panel

li

ght.

14

to center beam to iris #

in

the absence

li

ght).

18

and 23)

of

the seed beam, and the two intra-

If

this is not the case, reposition the irises

ONLY

Dr

ivers consequently disabling the RA

in

g directly through the center.

18

and then tweak mirror # 15 so that the

rs until the beam is

RA

cavity

do so when the

of

the SDG.

If

this is not

in

5.

Open fully the two irises.

6. Roll out the tim ing to

7. Switch the "output enable" to the upward position.

Observe Q-switch radiation from RA cavity using the Coherent photodiode.

8.

9. All

This completes the various procedures for optimizing the seed beam into the RA cavity.

ow seed beam

10

. While observing the buildup reduction make final tweak to the X

look

in

g for the greatest buildup reduction.

"output

to

propagate into RA cavity.

2" such

that the digital display indicates 500n

andY

-axis

s.

of

mirror # 14 while

C

COHEREnT

..

36 CHAPTER 5

5.4 Cavity Dumping a Pulse

While observing the regen cavity light with the photodiode, roll back the timing via "output 2" until the pulse prior to the "main" pulse

is

seen "cavity dumped" as shown in Fig. 5.3.

Fig. 5.3

Cavity

dumped

pulse

of

the SDG

CcoHEREnT..

37

6 Compressor Alignment Procedures

Fig. 6.1

Fig.

6.1

shows the top view

mirror set

compensates the second order dispersion, and rotating the component

dispersion (i.e. to

compensates the phase distortions introduced by the stretcher and reg. Amplifi get the shortest pulse duration. Typical pul shown

(#33), and one vertical retro-mirror

3rd

and

in

Fig. 6.2.

of

the compressor, which consists

4th

order). Therefore, by adjusting the components

Top

view

of

the

compressor

of

one grating (#32), one horizontal retro-

se

t (#34). Moving the component #33 back and forth

#32 compensates

se

dw·ation measured with single shot autocorrelator (SSA) is

hi

gher ord

#33,

and #32, one should be able

er

up to the

4th

er

order, and

Pulse

Fig. 6.2 44

fsec/IOOJ.lS

duration before deconvolution)

= 40 fsec

measured

C'

from SSA using

Gaussian

COHEREnT

deconvolution.

..

(Calibration

is

38

Before tuning the compressor, one should do the following alignment procedure for the compressor:

CHAPTER6

I)

Close the Pump laser shutter.

2) Disable the Legend-F High Speed Drivers.

3) Close the seed beam input shutter.

Warning: Failure to block the seed beam while performing this part

of

procedure will result in major damage to optical components in the regen. This

damage is not covered by the warranty.

The unseeded output

of

the regen

is

used for the first part

of

the compressor

alignment.

4)

Remove the grating assembly as

5) Install the removable reference iris

4mm.

Open the Pump laser shutter.

6)

7)

Enable the Legend-F High Speed Drivers and adjust the timing

dumping

8) Use mirror #26 to center the beam on the iris at position #31.

9) Disable the High Speed Drivers.

0) Move the iris to position #

I

II)

Enable the High Speed Drivers.

12) Use mirror

of

the Q-switched pulse.

#30

to center the beam on the iris.

7.

This part

in

step 7

in

location

of

the stretcher alignment procedure.

#3

I and adjust the aperture opening so that it

of

Pockets cell #2 so there is cavity

is

the reverse

of

the stretcher alignment steps 9-11.

the

is

~

5-

13) Iterate between steps

iris in

14) Leave the

15) Disable the High Speed Drivers.

16) Close the Pump laser shutter.

17) Install the grating assembly as in step I 4

Open the seed beam input shutter.

18)

19) Adjust the rotation as shown

the #31 location after the beam has been centered at both iris locations.

in

Fig. 6.3. Use an

12 until the beam

of

the grating assembly so that the stretched beam pattern on the grating appears

IR

viewer to verity this.

CcoHEREnT

is

centered on the iris at both locations.

in

Section 3, which is the stretcher alignment procedure.

e

COMPRESSOR

ALIG

NME

NT

39

Stretcher

20) Close the seed beam input shutter.

21) Disconnect the trigger BNC for High Speed Driver #2 on the SDG (output 2).

22)

Block assemblies #33 and 34.

23) Open the Pump laser shutter.

24) Enable the High Speed Drivers. This will produce a Q-switched pulse.

Open the seed beam input shutter.

25) buildup reduction, refer to the procedure

26) Connect the trigger BNC cable for High Speed Driver selecting the proper pulse to be switched out

Fig

. 6.3

grating

Spatially

•

input

beam

•

"stretched"

dispersed

If

spectrum

the seed beam alignment is not optimized for maximum

"o

ptimizing seed alignment" in Section 5.

of

the Regen cavity.

output

beam

on

the

stretcher

#2

on the SDG and adjust the timing for

grating

27

) VerifY that the seeded regen.

28) Using

Note:

On

reference

29) Unblock assembly #33 and u

theIR

viewer to look at the

ri

ght side

check the aligmne

chance

lines

l

eft screw See Fig. 6.5.

of the grating.

that

the

on

top

of

the

of

the input beam. The spectrum has to be on the same y-axis as the input beam. Use the x-axis

of

assembly #33 so that the input beam and the spectrum are on the same y-axis.

nt

throu

grating

Fig. 6.4

output beam is still centered on the iris.

gra

ting, one should see a round spot (input beam) on the lower

If

the input beam

gh

the iri

s'.

has

been

showing

Input

se

IR viewer to look at the grating.

removed

how

beam

on

is

not on the grating

from its

the

grating

the

mount

compressor

is

as

shown

and

put

positioned

grating

One

should see the spectrum to the

in

Fig. 6.4, go back and

back

in,

there

side

to

side

in

0

are

the

mount

C

COHEREnT

.

40

CHAPTER6

Do

not

make

adjustments with

they

axis screw on

0

mount

#33

Fig. 6.5

30)

The

input beam

The

spectrum should also be centered spectrum from side to side on the grating, loosen the and slide the assembly so that the spectrum is centered on the grating.

Spectrum to

and

the spatially dispersed spectrum by

in

be

centered from end

the remainder

of

114 x 20

grating to input beam I

the grating. See Fig.

screw at the back

-

c::

the

compressor grating

6.6.

To

of

assembly #33

..

I

0

I

Fig. 6.6

3

I)

Unblock assembly #34. Using the IR viewer, one should see the input beam and spectrum on the

bottom and the same pattern directly above. See Fig. 6.7.

Correct

position

of

the spectrum

0

center the

Fig. 6. 7

Correct

32)

If

the top two beams are not directly above the bottom two beams, the assembly #34 needs to be rotated. Loosen the 1/4 x 20 screw securing the assembly mount so that the top two beams are directly above the bottom two beams.

Do not make adjustments with

33) The top spectrum and spot should be assembly #34 so that they are on the same y-axis.

34) The top spectrum and output spot are centered on the grating See Fig. 6.8.

position

To

of

the spectrum on the grating

center the beams, assembly #34 may be moved vertically.

they

axis screw on assembly #34

in

the same y-axis.

C

COI-IEREnT

0

after

four path through the compressor

to

the breadboard and rotate the entire

If

they are not, adjust the x-axis screw on

in

the space above the bottom beams.

e

-

------------

Fig. 6.8 Correct position of the returning spectrum

COMPRESSOR

ALIGNMENT

41

35) Look at the output beam. There should be no clipping #34 and mirror

36)

If

adjustments are made with these mirrors, go back and look at the grating with

Verify that the beams are aligned as

of

any clipping

rid

#30 may

be

made

if

clipping is observed.

in

Fig. 6.7 and 6.8.

of

the output beam then the above procedure needs

of

the beam. Slight adjustments to mirror

If

large adjustments are necessary to get

to

be repeated.

theIR

viewer.

CcoHEREnT.

_

_)

J

Stretcher

43

7 Replacement Parts

Component#

I 705-2527 Dielectric HR

2

3 799

4

5 705-2527 Dielectric HR mirror, 750-900

6

7

8 710-2513

9

10

II

12

13

Part#

400-0848

-1

400-0848 Mech. Iris I

705-2527 Dielectric HR mirror,

400-0848 Mech. Iris

705-3447

705-4673

705-2528

705-2526

705-2527 Dielectric

Optical Description

miJTor,

Mech.lris

753 Ti:Sapphire optical Iso lator

Spectragon. Grat

Mirror,

I

l"xl"

6" dia, f = 36" Reflective gold I

"x7" Dielectric HR,750-900nm,O deg. I

"x3" Dielectric HR,750-900run,45 deg. 2

Dielectric HR,750-900run,45 deg. 1

HR

mirror, 750-900nm, I" 45 deg 2

750-900nm,

in

g, 30x110x16mm, 1200ln/mm

I"

run

, I" 45 deg

1"

45 Dg.

45 deg

Quantity

I

14

705-2527 Dielectric HR mirror, 750-900run,

I"

45 deg

CcoHEREn~

I

44

CHAPTER 7

Regen Amplifier Cavity

15 703-3641

16

17

18

19 705-2176

20

21

22

23

24 7 12-0793 Sol Gel Pockets Cell, 700-1

25

709-2215

7 12-0793 Sol Gel Pockels Cell, 700

400-0848 Mech. Iris 1

711-0750 1/4"

705-2176 Dielectric HR mirror, 750-900nm, I" 0 deg

708-0795 Kimetic BB polarizer, TFPK,528-RW-28

400-0848

703-3641

CVI mirror,

1/4 Waveplate, 0 order QWP0-825-05-4 I

Dielectric HR mirror, 750-900nm,

xI"

Mech. Iris 1

CV

I mirror, +90cm HR, 0 deg.

+90cm HR, 0 deg.

Ti:Sapphire rod 1

Telescope (8x)

26

705-2176

Dielectric

HR

-1

OOOnm

1"

0 deg

OOOnm

mirror, 750-900nm, 1" 0 deg 1

1

l

1

27 28 29

702-3649 701-0818 Lens, 705-2527 Dielectric

Lens, -50mm, BB , KPC040 AR.16

+400mm

, BB, KPX115-AR.16 1

HR

mirror, 750-900nm, 1"

Compressor

30 705-2526 1"x1" Dielectric HR,750-900nm , 31 32 33

33.5 34

400-0848 Mech. Iris 1 710-4735 Richardson Grating, 30x11 Ox16mm, 15001n/mm 1 705-4385

705-4734 705-2528 1"x3" Dielectric HR,750-900nm,45 deg. 2

1.5"x3"

1.5"x2"

Dielectric HR,750-900nm,45 deg . 1

Dielectric HR,750-900nm,45 deg .

45

dig

45

dig. 1

1

2

1

C

COHEREnT

..

45

8 Customer Service

At Coherent, we take pride in the durability manufacturing methods and quality control. Nevertheless, even the fine service.

8.1

Coherent warrants to the original purchaser that the equipment workmanship. Coherent will, without charge, make any necessary repairs such defect within one year, or the nature of

improper use. Coherent does not assume any liability equipment that impair or alter the normal functioning persons not expressly authorized by Coherent shall relieve Coherent

and remedy contained

COHERENT

WARRANTY shall

inconvenience occasioned by loss

authorized by Coherent.

Warranty

90 days

of

such defect within one year, or 90 days for optical surfaces, following the date

the equipment. The foregoing warranty does not cover equipment that has been damaged by accident or

in

this paragraph are the only warranty and remedy pertaining to the equipment.

DISCLAIMS ALL

OR

MERCHANTABILITY

in

no

event be liable for any incidental, consequential or other damages or costs, lost profits or

OTHER

of

our products. We place considerable emphasis on controll

in

the case

WARRANTIES, EXPRESS

the use

of

optical surfaces, provided that Coherent

if

adaptations are made

of

the equipment. Any repair or adjustment by

OR

FITNESS FOR A PARTICULAR PURPOSE. Coherent

of

the equipment

st

instruments need occasional

is

free from defects in material or

or

replacement

or

accessories attached to the

of all

obligations. The limited warranty

OR

IMPLIED, INCLUDING

or

labor expended by persons not so

of

parts to remedy

in

writing

of

original sale

ed

of

8.2 Return of the Instrument for Repair

Contact your nearest Coherent field sales office, service center,

or an on-site

instrument to Coherent.

We encourage you to use the o

· destroyed containers.

se

rvice appointment. You are responsible for one-way shipment

ri

ginal shipping boxes during shipment.

or lost, we recommend you order new ones. We can return instruments only

C'

COHEREnT

or

local distributor for shipping instructions

ofthe

defective

If

shipping boxes have been

in

Coherent

patt

or

.

_J

I

_J

MANUAL

ADDENDUM

HIGH-ENERGY

LEGEND-HE

VERSION

J

• J

Preface

Copyright

or

means, copying includes translation into another language.

Coherent, the Coherent logo, design marks, and all other Coherent products mentioned herein are the registered or unregistered trademarks holders and are hereby acknowledged.

Disclaimer

stored

of

in

a database

1976, no part

or

of

Coherent, Inc. All other trademarks

of

this publication may

retrieval system, without the prior written permission

be

reproduced or distributed in any form or by any

of Coherent. Under the law,

or

service marks are the property

of

their respective

This manual provides information regarding the operation and maintenance

Every effort has been made to ensure that the information document is subject

implied with respect to this document. In no event will Coherent be liable for any direct, indirect, special, incidental

or consequential damages resulting from any defects

Coherent personnel will install the laser system. We do not guarantee laser performance unless the laser is installed by Coherent personnel or by an authorized representative

Support

If

Needs

you have any technical questions or problems, please contact Coherent:

to

change without notice. Coherent makes no representation or warranty, either express or

in

this manual is accurate. All information

in

this documentation.

of

Coherent.

of

the Coherent Legend-HE.

in

this

Coherent, Inc.

5100 Patrick Henry Drive

Santa Clara,

Tel: 408.764.4000

[email protected] www.coherent.com

Manual: Version

Updated: June

Printed: August 23, 2006

19

CA

1.

,20

95054

1

03

C

coHER

EnT*

1 System Description

1.1

Congratulations on your purchase Ti:Sapphire regenerative amplifier with a stretcher and compressor, high speed synchronization electronics, and computer-controlled electronics to provide thermal management

This manual addendum describes the features and operation a standard Legend, specifically the Environmental Control Unit (ECU), the control software for the ECU, and the

layout

refer to the standard Legend manual.

Introduction

of

the Legend-F-HE. The Legend-F-HE is a high-energy, kilohe11z rep-rate,

of

the regenerative amplifier (regen).

of

For

the setup and operation

of

the Ti:Sapphire las

the components

of

the rest

er

rod.

of

the Legend-F-HE that differ from

of

your Legend system, please

1.2 Theory of Operation

The Legend-F-HE differs from a standard Legend in two main areas: the regenerative amplifier design and the thermal management common to most Legends, has been optimized for efficiency and stability Ti:Sapphire rod precisely aligned and focused in the Ti:Sapphire rod to match the lasing mode defmed by the regen cavity.

To

compensate for the increased heat load in the Ti:Sapphire rod due to the high pump power, the rod assembly is actively cooled embedded RTD sensor, and the temperature 0-5° C. The hot side embedded thermistor temperature senso

of

the Ti:Sapphire laser rod.

is

pumped from both sizes by a single, high-power Evolution pump laser. The two pump beams are

by

a thermoelectric cooler (TEC). The temperature

of

the TEC is regulated by contact with a water-cooled copper heat sink which contains an

r.

The

regen cavity design, based

in

of

the rod assembly

is

regulated to maintain optimum performance, typically

on

the compact z-fold cavity

high pulse energy performance. The

is

monitored through an

in

the range

of

To

prevent condensation at low operating temperatures, the top

with dry air continuously circulated through this housing. Brewster-angle windows are attached at both ends

housing to transmit the regen and pump beams. The housing also contains a humidity sensor to detect whether the air

is

inside the housing

The ECU comprises hardware and software that enable the temperature HEto be controlled automatically in conjunction with the operation control circuit includes a commercial temperature controller (Watlow 96) for adjustment and monitoring and sends a control signal to the power supply for the TEC interlock electronics monitor the humidity sensor and the thermi stor in the cool prevent the operation sink exceeds a safe operating temperature. The ECU also contains a small air pump and two desiccant cartridges that supply dry air to the laser rod housing.

adequately dry to prevent condensation at the operati

of

the Ti:Sapphire temperature.

of

the TEC

if

there

of

the rod assembly

ng

temperature

of

the Ti:Sapphire rod in your Legend-F-

of

the Evolution pump laser. The temperature

The

temperature controller monitors the

to

regulate the temperature.

is

high humidity in the laser rod housing or

CcoHEREnT.

is

enclosed in a sealed housing

of

the Ti:Sapphire rod.

of

the temperature set-point

RTD

in the rod assembly

The

ECU al

ed

copper heat-sink. The interlocks

if

the temperature

so includes

of

the heat

of

the

2

LEGEND-HE

ADDENDUM

The temperature regulating functions

panel

of

the ECU. The pre-installed software for the Legend-F-HE enables the user to set and monitor the temperature the laser rod temperature based on the operating state

of

the laser rod. The software also works

of

the ECU can be controlled by computer through a USB interface on the front

in

conjuncti

of

the Evolution.

on

with the Evolution control software to change

1.3 System Layout

The standard component layout for a typical Legend-F-HE system, including the Evolution pump laser, Mira seed oscillator, and Verdi pump la

se

r, is shown in Figure

1.

Figure

1:

Standard

Evolution-30 pump and Verdi-pumped

optical layout for a Legend-F-HE system with

Mira

seed laser.

CcoHEREnT

.

an

1.4 Regenerative Amplifier

1.0 SYSTEM

DE

SCRIPTION 3

The optical layout collimated into each side mounted on the laser rod housing.

Refer to the standard Legend manual for a detailed explanation amplifier.

by

of

the regenerative amplifier is shown a telescope and then split of

the Ti:Sapphire rod. The seed light from the stretcher is reflected from one of the Brewster windows

Figure 2: Optical layout

50150

by a dielectric beam splitter. Each pump beam is aligned and focused

of

in

Figure 2.

the Legend-F-HE regenerati

The

Evolution pump beam

of

the other components

ve

amplifier.

is

expanded and

of

the regenerative

1.5 ECU

The ECU electronics are contained

as the Evolution power supply.

Front panel connection

s:

• POWER LED- illuminates when the ECU power

• HUMIDITY FAULT LED - illuminates

• CHILLER FAULT LED - illuminates

heat sink (e.g.

ifthe

chiller is turned

• USB - A-type female connection for connecting

male cable.

• TE COOLER CONTROL - front panel display

shows the measured temperature temperature.

Back panel connections:

• OUT & RETURN - Quick-connect supply and return fittings for the dry air loop.

• TEC - Hybrid D-sub electrical connector

umbilical.

•

On/Of

f switch for the

ECU

in a 3U

with an integrated fuse and IEC-320-Cl4 power connector inle

rack-mount enclosure (Figure 3) designed

is

on.

if

there

is

a high-humidity interlock condition in the laser rod housing.

if

there is a high temperature interlock condition in the water-cooled

off when

of

the laser rod mount; the bottom display in red shows the

the

TEC

is cooling).

to

the control computer using the supplied USB A-male to A-

of

the Watlow temperature controller.

to

connect to the side-panel

of

the Legend-F-HEusing the included

to

be mounted

The

in

the same rack

top display in green

set

-point

t.

CcoHEREnT

.

4

LEGEND-HE

ADDENDUM

$~------------------------------------------'$

ECU

POWER

0 0 0

o

USI

CJo

TE

COOLER

CONTROl

D

•

POSITJVB

LIGHT

0

TEC

our

Figur e

3:

Front-

0

and

0

back-panel

of

1.6 Software Control

The Legend-F-HE control software includes a window running a version the Evolution manual for a description Figure 4.

of

these controls) and a window running the ECU control panel shown in

0

the ECU.

of

the Evolution control software (refer to

Fig

ur

e 4:

The controls for the

•

STOP

•

TI:SAPPHI contro software is running, the state point) or not lasing (Warm set-point). Evolution software

ECU software are:

ECU

- Button to stop the ECU software and save the changes made to the other settings .

RE

SETPOINT

ll

er

between a the Cold set-point and the Warm set-point. Note that when the Evolution control

ECU control

- Toggle switch control to change the setting

of

this control is determined by whether the Evolution is lasing (Cold set-

panel in

Legend-F-HE

is

stopped, the user can toggle the set-points.

control

softwar e.

of

the ECU temperature

Ccot-tEREnT.

1.0 SYSTEM D ESCRIPTION 5

•

TI:SAPPHIRE as detected by the

•

PERCENT OUTPUT supply. The range is

•

COLD

in

•

WARM is in the ' usually th e same as the set-point

•

"AT point and the actual Ti:Sapphire temperature. When this difference is less than the value set, the point" this setting has no effect on the function

SETPOINT

the

'Co

SETPOINT

SETPOINT"

LED illuminates. Units are degrees Celsius, and typical values for this parameter is 2.0. Note that

TEMPERATURE

ECU temperature controller. Units are degrees Celsius.

- Indica

0 to -90.

[C) - Control for the set-point

ld'

position. Units are degrees Celsius, and typical values for this parameter are 0 to 5.

[C]

- Control for the set-point

Wann

' position. Units are degrees Celsius, and typical values for this parameter are 20

THRESHOLD

- Indicator showing the temperature

tor

showing the percentage

of

the Evolution water chille

[C) - Control for the threshold difference between the temperature set-

of

the ECU.

of

maximum output

of

the laser rod temperature when the set-point switch is

of

the laser

rod

r.

of

the Ti:Sapphire laser

pow

er

temperature when the set-point switch

of

the

TEC

rod

power

to

25,

"

At

mount

Set-

TI:SAPPHIRE

• temperature set-point and the actual Ti:Sapphire temperature

indicator is meant as a convenience to the user point.

•

ECU

COM

factory and should not

•

ECU

COMM

control laptop and the

Note that the ECU control software only interacts with the temperature controller in the ECU. interlocks is not monitored technician who with the

in

stalls your Legend-F-HE laser. Under

ECU software except to monitor the perfonnance

AT

PORT-

ERROR-

TEMP

by

SETPOINT

Control to set the communication s port associated with the ECU. This is set at the

be

changed.

LED indicator that illuminates when there is a communications error between the

ECU.

the ECU software.

- LED indicator that illuminates when the difference between the is

less than the " At Setpoint" Threshold. This

to

The

quickly detennine

settings

of

the ECU software will

nonn

al circumstances there is no need for user interaction

of

the temperature controll

if

the T i:Sapphire

be set

er

in the ECU.

is

at the proper set-

The

status

of

by the service

the ECU

CcoHEREnT.

J

_J

I

_j

I

-.J

_j

7

2 Legend-F-HE Operation

2.1

Eyewear Required

2.

TE Cooled Legend Start-up Procedure

-··-,til

1.1

Short Pulse Oscillator:

1. Turn on the external city water supply

Tum

2.

3. Initiate the

on the chiller corresponding to the short pulse oscillator

"turn-on" system manual. Allow ample warm-up time following turn on for the oscillator to thermally stabilize. Following ample war-up time, ensure optimum power and wave length.

The following procedure will result in a laser beam being emitted from the Legend output port. Ensure all room are wearing adequate laser eye protection. Ensure that the

anticipated beam is terminated.

if

any part

procedure for standard operation

2.1.2 Environmental Control Unit (ECU):

per

sons

in

of

the short pulse oscillator requires so.

if

one

is

required.

of

the short pulse oscillator as described in the

the

1.

Tum

"On"

the AC switch located behind the back panel.

2.1.3 Evolution Diode Pump Laser:

1.

Tum

"On"

the Chiller AC switch.

2. Initiate the tum on procedure for operating the Evolution laser via the control computer.

3. Depress the Evolution AC switch located on the left side position. The switch will illuminate following tum on.

4.

Tum

the key located to the right

5.

On the control computer, open the program labeled

6.

Tum

on the Positive Light Evolution laser by pressing on the

software. Doing so will set the

of

the

AC

ECU to the

C

of

the front panel

circuit beak

'Cold' temperature set-point.

COHEREnT

er

clock-wise, to the

"Lege

nd-F-HE

"ON"

.

Control"

button

of

the Power Supply to the

"ON"

position.

of

the Evolution control

"1"

8

LEGEND-HE

ADDENDUM

2.1.4 Synchronization Delay Generator (SDG):

1.

Turn on the SDG. Ensure that the SDG module switch controlling delay output 1 is off. The corresponding LED is will not

if

Note: the user may operate the regenerative amplifier unseeded with the Tsunami las

sync enable switch to off.

the Tsunami laser

be

illuminated when in the

is

not turned on then the SDG will give a "sync error" indication. By overriding the BWD,

off

position.

2.1.5 5 kHz Power Supply (5 kHz systems only):

er

turned

off

and switching the SDG

1.

If described later in the standard Legend manual.

Tum

on the external 5

unit.

the system operation does not work as described above, it may be necessary to follow more detailed procedure

KHz

High Speed Driver power supply via the AC circuit breaker located behind the

2.2 Legend Shutdown Procedure

1.

Stop the Evolution lasing by pressing the red "STOP" button located on the computer screen via the control computer. Doing so will cause the ECU to set the Ti:Sapphire rod temperature to the 20

C).

Stop the Evolution control software by pressing the "Stop and Save Settings" button.

2.

Stop the ECU control software by pressing the "STOP ECU" button.

3.

4. Disable the Evolution power supply by turning the

5. Depress the Evolution power supply circuit breaker to the

6.

Tum

"off'

the Evolution Chiller .

7. Turn

off"OUT

time it is to be used with this

1" on the SDG. This disables the regen from working. It

in

the

off

position.

"on/off'

key counter-clock-wise to the "OFF" position.

off

position "0".

is

also good to start the system next

'Warm'

set-point (e.g.

8.

Power

"off'

the SDG.

9. Power

10.

11

. Power down the short pulse oscillator/pump source as described in its system manual.

12.

off

the

"on/off'

Tum

off

the

"on/ofr'

systems only).

If

necessary, replace the Legend external covers on the Legend breadboard.

switch corresponding to the ECU unit.

switch corresponding to the

C

COHEREnT

5kHz,

High Speed Driver power supply module

.

(5kHz

9

3 Trouble-Shooting

This chapter contains a general user-troubleshooting guide. problems that might arise while using the system. A complete repair procedure For problems that you cannot solve using this guide, contact your authorized service representat ive.

3.1

Use this guide

to

assistan ce.

Trouble-Shooting Guide

ifyour

Legend-F-HE performance drops unexpectedly.

bring your Evolution-IS performance up

to

specification, call your authorized service representative for

It

is provided to assist you in isolating some

is

beyond the scope

If

you try the corrective actions and are unable

Symptom: Ti:Sapphire rod will not reach set-point temperature

Possible Causes

Humidity interlock

Temperature interlock Trouble-shoot temperature fault (see below)

Wat

er

temperature set Ensure that the water chiller temperature is set

incorrectly (typically

Trouble-shoot humidity faul t (see below).

20 C).

Corrective

Ac

tion

to

its factory value

of

the

of

this manual.

Pump laser power set too high Ensure that the Evolution pump laser is operating at the same power

level as when the laser was installed.

Symptom: Comm error in control software

Possible Causes

USB cable unplugged

C

OM

port set incorrectly

Evolution or not turn

ECU power supply Ensure that both power supplies are turn

ed

on. Legend-F-HEsoftware.

Stop and close software. Check Evolution and

Ref

er to the original values

installation. Adjust settings as needed.

C'

ECU. Plug b ack in

COHEREnT

Corrective Action

USB cable connections

if

necessary. Restart software.

of

the CO M port settings at the t ime

ed

on before launchi

.

to

the

ng

of

the

I 0 LEGEND

-HE

ADDENDUM

Symptom: Humidity interlock illuminated

Possible Causes

ECU

just

started up Wait a few minutes for the ECU

rod housing.

Air hoses disco nnected or kinked Check quick-connects on back

panel ofLegend-F-HEand on laser rod assembly.

Air pump not running

Desiccant cartridges consumed

Humidi

ty sensor disconnected Check connections at the laser rod assembly.

Listen for sound contact your service representative for repair.

Look through window in top cartridges have turned completely pinkish from exposure to moisture.

Replace cartridges

of

Corrective Action

air pump.

if

necessary.

Symptom: Temperature interlock illuminated

Possible Causes Corrective Action

to

pump dry air through the laser

of

ECU, check hose-barbs on side

IfECU

ofECU

is on and pump is not running,

to see

if

both desiccant

Water hoses disconnected or Check water connections from Evolution to the hose-barbs on side kinked panel

Wat

er chiller not running

Temperature

disconnected

se

nsor

ofLegend

Tum

on water chiller.

Ch

eck connections at the laser rod assembly.

-F-HEa

nd

on laser rod assembly.

C

COHEREnT

.

C COI-IEREnT®

USER

MANUAL

SYNCHRONIZATION

AND

DELAY

SDGII

GENERATOR

J

.._.

_J

I

--'

.J

_j

I

Copyright

Preface

of

United States Copyright Act form or by any means, or stored in a database Coherent. Under the law, copying includes translation into another language.

Coherent, the Coherent logo, design marks, and all other Coherent products mentioned herein are the registered or unregistered trademarks property

Disclaimer

This manual provides information regarding the operation and maintenance

Every effort has been made to ensure that the information document is sub or special, incidental or consequential damages resulting from any defects in this documentation.

Coherent personnel will install the la

installed by Coherent personnel or by an authorized representative

Support Needs

If

of

their respective holders and are hereby acknowledged.

ject

to change without notice. Coherent makes no representation or warranty, either express

implied with respect to this document. In

you have any technical questions

1976, no part

of

se

or

of

this publication may be reproduced or distributed in any

or

retrieval system, without the prior written permission

Coherent, Inc. All other trademarks or service marks are the

no

event will Coherent be liable for any direct, indirect,

r system. We do not guarantee laser performance unless the laser

problems, please contact Coherent:

in

the U.S.A. Except as permitted under the

of

the Coherent SDG.

in

this manual is accurate. All information

of

Coherent.

in

of

this

is

Coherent, Inc.

5100 Patrick Henry Drive Santa Clara, CA

Tel: 408.764.4000

[email protected] www.coherent.com

Manual: Version

Updated: May 1996

Printed: August 23, 2006

95054

1.1

e

COHEREnT

.

.J

- J

Inputs (trigger input and RF synchronization)

Specifications

Trigger Input

RF Sync

TTL compatible,

10-100

MHz

, > 100 mY peak to peak

Outputs: (one fixed and three variable delay

Fixed delay

Adjustable delays

Jitt

er

High Voltage

+200 ns (±ns)

0 - 1250 ns in 0.25 ns steps

< 250

ps

with respect

1 kV - 6kV

DC

for input

0-50 kHz

s)

to

RF cycle

to

HSD (high speed driver)

Table of Contents

1 Laser Safety ...................................................................................................................................................... I

1.1 Hazards ............................................................................................... .................................................... I

1.2

Optical Safety ............................................................................................................................... .......... I

1.3 Electrical Safety Precautions ................................................................................................. ................. 2

1.4 Protective Eye W

1.5

Sources

1.5

1.5.2 Equipment and Training ....................................... .......................................................

of

.I

Laser Safety Standards ............................................................................ .................................. 3

2 Product Overview ...... ....................................................................................................................................... 5

2.1 Background ........................... ................................................................................................................. 5

3 Set-up

and

Operation ...................................................................................................... ................................. 9

3.1

SDG

II

Set-up and Connections ............................................................................................................. 9

3.1

.1

Voltage Selection ............ .................. .................................. ................... .... ................................ 9

3 .1.2

3.2 SDG

3.2.1 SDG

3.2.2 Front Panel Controls and Connections ................ ....................................................................

3.2.3 Back Panel Controls and Connections .....................................................................................

3.3 SDG

3.3.1

3.3.2 RS-232 Communication Protocols .......................................................................................... 13

3.3.3 Command/Query/Response Format ...........................................................

3.3.4 Command Quick Reference ...........

3.3.5 Full Command Description ...................................................................................................... 14

3.3.6 Limitations

3.3.7 Typical Cotnmand

Set-up for Photodiode Synchroni

II

Detail

II

Computer Interface .................................................................................................................. 13

RS-232 Connector Wiring .................................................................................................. .....

ear

............................................................................................................................... 3

Additional Information .................................................................................... ..................... 3

..

............ 3

za

tion ................................................................................... I 0

ed

Description .......................................................................... ...................................... 10

IIO

ptions ..................................................................................................... .......... .........

..

............................ 13

.. ..

...............................

ofRS-232

Control

Usage .........................................................................................................

ofthe

SDG !!... ....................................................................... 16

....

................................................... 14

IO

11 12

13

16

4 Regenerative Amplifier Alignment ............................................................................................................... 17

4.1

Static Regenerative Amplifier Alignment

4.

1.1

Pockels Cell Alignment ...........................................................................................................

4.1.2 Polarizer Alignment ................................................................................................................. 19

4.1.3 Lase

4. l .4 Mirror Alignment. ....................................................................................................................

4.2 Lasing Optimization .................................................................. ........................................................... 20

4.3 Seed Alignment ............................... ................................................................................. .................... 23

4.4 Regenerative Amplification ...................................................................... ............ .

5 Customer Service ............................................................................................................................................ 27

5.1 Warranty ............................................................ .................. ....................... .......................................... 27

5.2 Return

of

..........................................................

rRodAlignment

the In strument for Repair ................ ..................................................................................... . 27

...............................................................................................................

...

........

..........

..

............................. 24

17 18

l9

19

CcoHEREnT.

Warning Conventions

The

following warnings are used throughout this manual to draw attention to situations require extra attention. They warn and exceptional circumstances.

of

hazards to your health, damage to equipment, sensitive procedures,

or

procedures that

Eyewear Required

Laser radiation present

Safety eyewear required

C

COHEREn

T.

Caution!

1 Laser Safety

-Use

of

controls or adjustments or performance ofprocedures I

other than those specified herein may result

radiation exposure.

in

hazardous

This safety section should be thoroughly reviewed prior to operating the Safety precautions contained herein and throughout the manual must be carefully followed to ensure that all personnel who operate or maintain the laser are protected from accidental

radiation.

The Coherent designed to facilitate the amplification exposure hazard. particular, read the safety sect exposed to.

This safety chapter should not be construed as a substitute for the safety sections in the manuals provided with the lasers you operate. It

1

.1

Hazards associated with lasers generally fall into the following categories:

•

SDG II is not a laser and as such does not present a laser hazard. However the SDG II

of

short laser pulses. Use

It

is imperative that the user familiarizes himself/herself with all aspects

ion of

all the laser manuals provided with equipment you operate

is

intended as an additional guide to laser safety.

Hazards

Exposure to laser radiation which may result in damage to the eyes or skin .

Exposure to chemical hazards such as particulate matter of

laser material processing,

Electrical

Secondary hazards such as:

1.

ha

zards generated in the laser power supply

X-radiation from faulty power supplies

or

a by-product

of

the lasing process itself.

or

SDG II described in this manual.

or

unnecessary exposure to laser

of

the SDG II therefore presents a laser

oflaser

or

gaseous substances released as a result

associated circuits .

safety. In

or

are

is

2.

Pressurized lamps, hoses, cylinders, etc.

3.

Pressurized liquids and gasses.

1.2 Optical Safety

The special nature All users

of

laser light poses safety hazards not associated with light from conventional sources.

lasers must make themselves familiar with the special hazards associated with their operation.

C

COHEREnT

.

2 CHAPTER 1

The safe use should be worn at all times.

The

following safety precautions are to be read and observed by anyone working with the SDG II:

• Wear protective eyewear at all times; selection depends on the wavelength and intensity

• A void wearing jewelry

• Use an infrared detector to verify that the laser beam is on

• Observe all safety precautions in the operator' s manual.

• Never look directly into the laser beam.

• Set up controlled access areas for laser operation. Operate lasers only in well marked areas with

•

• Limit access

• Terminate the laser beam.

• Work with the lowest energy consistent with the application.

• Eliminate unnecessary reflections and scatter

• Work in high ambient illumination.

of

the SDG II requires that all users are familiar with its operation. In particular, eye protection

radiation, the conditions

listed

in

the Laser Focus World, Lasers

Consult the

controlled access. Be sure to post appropriate warning signs visible to al

The

use, lasers should be shut down completely and made off-limits

ANSI, ACGIH,

operation

of

to

the laser system

of

use, and the visual function required. Protective eyewear vendors are

and

Optronics, and Photonics Spectra buyer's guides.

or

OSHA standards listed at the end

or

other objects that may reflect

lasers should be under the supervision

to

persons required to be present.

ed

laser radiation.

of

this section for guidance.

or

scatter the beam while using the laser.

or

off

before working on the laser.

l.

of

qualified personnel only. When not in

to

unauthorized personnel.

of

the

• Maintain experimental setups at low level to prevent inadvertent eye encounter with beams.

• Follow the instructions in this manual.

1.3 Electrical Safety Precautions

• Disconnect main power lines before working for the equipment to be operating.

• Do not short or ground the power supply output. Positive protection against possible hazards requires proper connection

ground. Check these connections at the time

• Never work

operation and hazards

• When possible, keep one hand away from the equipment to reduce the danger

through the body

• Always u

• Special measurement techniques are required for this system. Ground references must be selected by a technician who has a complete understanding

electronics.

on

electrical equipment unless there is another person nearby who

if

a live circuit

se

approved, insulated tools when working on equipment.

of

the ground terminal on the power cable, and an adequate external

of

the equipment, and who is competent to administer first aid.

is

accidentally touched.

on

any electrical equipment when it

of installation, and periodically thereafter.

of

the system operation and associated

is

not necessary

is

familiar with the

of

current flowing

C

COHEREnT

.

1.4 Protective Eye Wear

It

is recommended that laser-safe eye wear is worn at all times. See the manual provid

system for guidelines

LA

SER

SAFETY 3

ed

with your laser

1.5 Sources

The following are some sources for additional information on laser safety standards and safety equipment and training.

of

Additional Information

1.5.1 Laser Safety Standards

SAFE

USE

OF LASERS(Z136.1)

AM

ERICAN

NATIONAL

(ANSI)

1430

BROADWAY NEWYORK,NY 1001 8 TEL:

(212) 354-3300

A

GUIDE

A

MERICAN

AND INDUSTRIAL

6500

CINCINNAT TEL:

FOR CONTROL

CONFERENCE

HYGIENISTS

GLENWAY

I,

OH

AVENUE,

45211

(513) 661-7881

STANDARD

OF LASER HAZARDS

OF

S I

NSTITU

GOVERNMENTAL

(ACGIH)

BLD

G.

D-7

TE

OCCUPATIONAL

ADMINISTRATION

U.S. D 2

WA

LAS

EPARTMENT

00

CONSTITUTION AVENU

SHINGTON,

ER

SAFETY

LASER

12424

INSTITUTE

RESEARCH

SAFETY

DC 2021 0

GUIDE

130

ORLANDO,

TEL:

FL

32826

(407) 380-1553

AND H EALTH

(OSHA)

OF

LABOR

E N.W.

OF AMERICA PARKWAY, SUI

TE

1.5.2 Equipment and Training

LA

SER

FOCUS BUYER's

LASER ONE

P.O. W

TEL:

LASERS AND

LASERS

301 P.O

MORR

FOCUS

WORLD TECHNOLOGY

Box989

ESTFORD,

MA 01886-9938

(508) 692-0700

0PTRONICS

AND OPTRONICS

GIBRALTAR DR.

.Box6

50

IS

PLAINS,

TEL:(21 0)292-5100

GUIDE

PARK

B UYER'S GUIDE

NJ

07950-0650

DRIV

E

PHO

P

BERKSHIRE PITTSFI

TE

CcoHEREnT

TONICS SPECTRA

HOTONICS SPECTRA

COMMON

ELD,

MA 01202-4949

L:

(41 3) 499-0514

.

BUYER'S

GUIDE

_.

I

5

2 Product Overview

2.1

Regenerative amplifiers, seeded by low energy laser pulses, are an extremely efficient means energy, high peak power pulses. The principle pulse (selected from a mode-locked train), amplify Typically rod, for example. This represents an overall amplification optical pulse passes through the laser rod, which has been optically excited. Normally the amplification rod multipass the rod resulting in a much higher overall gain.

The amplification

operating at many

facilitated by precisely controlled fast electronics. The SDG II is designed to control the timing between a mode-

locked seed source and an amplifier. In a typical configuration a

of

mode-locker to the

mode-locked laser) to the

Following synchronization, four delayed trig steps. Typically, two laser Q-switch or oscilloscope. to adjust the output repetition rate to values below the master input rate. The controlled, and all delays are digitally displayed and accessible via front panel knobs and a rear panel connection.

Background

of

obtaining high

of

regenerative amplification

it

to an appropriate ener

an

input pulse

is

small, only about 3-4 in single pass, however the regenerative amplification technique enables the pulse to

a mode-locked laser and a Q-switch driver (HSD). This is accomplished by coupling the RF pulse

of

energy only a few nanojoules can be amplified to over

of

greater than l o

of

short laser pulses is dependent upon proper timing between the seed-source pulse train

MHz

and the amplifier resonator typically pumped at 1-5 kHz. Proper timing can only

SDG II enables synchronization between the output

SDG II. Similarly the output

SDG II. The input is synchronized precisely to the RF signal by hi gh-speed electronics.

of

these are used to trigger Pockels cell drivers and the other(s) is/are used to trigger a pump-

An

additional feature is

of

a fast photodiode can

ge

r signals are produced: one fixed and three user-adjustable in 250 ps

an

integrated countdown circuit that allows the experimenter

is

to confine, by polarization, a single

gy

level, then cavity dump the output.

lmJ

in a sing

6.

The amplification takes place as the

be

coupled (detecting the pulse train

SDG

II

module is microprocessor

le

Ti:Sapphire laser

of

RS-232

of

the laser

be

the laser

of

the

of

A prerequisite two or three nanoseconds will result in multiple output pulses. Hence the timing associated with firing the

cells is criti

the resonator. In order to ensure a single pulse is admitted to the resonator, the

same time, with respect to the mode-locked pulse train (the seed pulses), every time. To achieve this, switching is synchronized to the RF signal generated by the mode-lock switching (the time at which the synchronization, there is a adjustment are contained

be provided by the use The second Pockets cell switches the pulse out trips and so a delay

delay adjustments on the timing electronics - the first provides a trigger to

PC2.

regenerative amplifiers is the switching

cal. In a regenerative amplification system alluded to above the first Pockets cell switches the pulse into

0-200ns delay that allows phase adjustment. The synchronization electronics and phase

in

SDG II module. The SDG II module

r.

The SDG II then produces separate triggers, with adjustab

of

approximately 200ns is required after the first Pockels cell switches. There are two adjustable

of

the Pockets cells at the correct timing - an error

Pockels cells must be switched at the

er

of

the seed laser. Additionally, the phase

Pockets cells switch with res pect to the pulse train) must be adjustable. Following

is

triggered by a TTL positive edge pulse that must

le

delays, to the Pockels cells.

of

the resonator. The pulse must be ejected after

PC

l , and the second provides a trigger to

C

COHEREnT.

suf

ficient round

of

Pockels

the

only

6 CHAPTER2

Pump Laser

Trigger

(pump

Figure oscillator, which produces approximately amplifier to be stretched, amplified and then recompressed. The regenerative amplifier is pumped with a frequency doubled Nd:YAG

A typical optical arrangement is illustrated below:

In

Q-switch)

2.1 shows a typical amplification system. A pump

I

orNd:YLF

..

SDG II Mode Locked

Output

(drives

500mW

laser.

Regenerative Amplifier

Laser

t n

II

train

Output

(drives

(80

2

PC

MHz)

..

I I

I

1

PC

1)

la

ser provides energy to a cw mode-locked Ti:Sapphire

of

ultrashort pulses. These pulses are directed to the regenerative

J

RF

signal

mode locked pulse

2)

Figure 2.2:

Ml

M

PCI

WPl

Rl

Optical

---I

AI

--=--t -.-il

l,M

2

components

INP

UT

-+-8-t---:f::=J-

Pump beam

Resonator end mirror

Input

Quarter-wave plate.

Ti:Sapphire laser rod.

of

a typical amplifier system

Ll

Pockels cell.

OUTPUT

'\.~

.......

--+

D-!---.-1

PI

AI

PI

PC2

Ll

PC2

Aperture

Output polarizer

Output Pockels cell.

Pump beam focusing lens

M2

CcoHEREnT

.

PRODU

CT OVERVIEW

7

Operation

I.

2. The mode-locked pulses are injected into the regenerative amplifier by reflection

3. While the input

4. The pump laser Q-switch is activated providing a pump pulse to the Ti:Sapphire laser rod. This is the

We now consider the pulse that will be amplified:

5. The pulse enters the resonator by reflection

6. The pulse passes through

7.

8. After a number

is as follows:

The pulses from the pulse stretcher are directed into the regenerative amplifier laser cavity.

off

(R

l).

Pockels cell

and exit again, receiving little

time when the

Pockels cell,

is

deactivated, the pulses make a single round-trip through the Legend

or

no amplification.

PCl,

is activated to begin the amp lification process.

off

the laser rod.

/J4 plate and Pockels cell, which

is

off.

It

is

reflected by mirror M I and thus retraces its path. Because it has double passed the wave plate it has undergone a is transmitted by the las

As soon as the pulse leaves Pockels cell Pockels cell is now effectively a

er

rod and the other resonator optics.

PCI,

quarter-wave voltage (3500V) is applied to

/J

4 plate and so negates the effect

of

the wave-plate. The pulse

trapped in the resonator.

of

round trips, usually about 20, a quarter-wave voltage is applied to the output Pockels cell, causing a pulse

is

thus ejected from the resonator by the polarizer.

multipassed the rod and experienced a gain

half

wave rotation to the pulse after it has double passed the Pockels cell. The

WhHe

trapped in the resonator the pulse has

6

of

over 10

.

the laser rod

/J

2 rotation and

it.

The

is

CcoHEREm.

8

It

resonators. The primary difference merits, at Coherentwe normally use two other to switch it out, as described above. However each method requires two we SDG II will provide (see figure 2.3).

CHAPTER2

is important to note that there are various schemes for switching pulse in and out

is

the number

Pockels cells

of

Pockels cells used - either one or two. Both methods have their

in

our regenerative amplifie rs, one to switch the pul

of

regenerative amplifier

se

in, the

ll

-defined trigger signals, which the

Input Trigger

1-5kHz

_n n

.____

~

RF pulse tra

-

80MHz

Figure 2.3: Schematic r

seeding laser and the outputs amplifier cavity respectively, switching in a single pulse (via delay 1), and following amplification, switching out a single pulse (via delay 2). Note:

in

ep

resenti

ng

synchronization between the

of

the SDG II (delays 1 and 2). These outputs trigger Pockels cells I and 2 within the

Coordinate(s) not to scale.

Input

.gw:.-

\ nl"l:'tv 1 '

~------------

---=--=-

-------------'

---v-

RF

signal (red) originating form the mode-locked

C

COHEREnT

.

3 Set-up and Operation

Laser radiation present

9

Eyewear Required

3.1

3.1.1

Normally the SDG II is shipped configured for use with

country where typical line voltage is compatible with this vo ltage. In this event the ac line port, on the rear 220 Vo lt Operation". If it is not marked in this manner, you must ensure that your SDG II is set-up for operation at the correct input voltage.

To check the line voltage selection:

I. Disconnect the line voltage from the SDG II.

2. Remove the cover.

3. Close to the two transformers, at the rear right

SDG

Voltage Selection

The silk-screen on the printed circuit card indicates the position

the input voltage.

~

Safety eyewear required

-

-·

II

Set-up and Connections

200 - 240 volts, then the SDG II will be set-up

100-120

ofthe

unit there are jumpers marked J25 through J28.

volt line. If the unit is shipped to a

at

Coherentto be

of

the SDG II, will be marked "

of

the jumpers required depending on

200-

4. Insure the jumpers are in the correct position to be compatible with the line voltage in your laboratory.

5. Replace the cover.

As already stated the SDG EXT TRIGGER in frequency . These outputs can also be synchronized with an RF signal from a mode locked laser or photodiode, also the below).

In order to connect the SDG II to your laser

1.

Connect a BNC cable from the output trigger "Trigger In". Wh en using a Coherent" Evolution connect the BNC on the rear panel BNC on the SDG II labeled "Trigger In".

II provides 3 adjustable delay outputs and I fixed output that corresponds to the

ou

tput frequency can

fo

llow these instructions:

of

the Evolution X laser power supply marked "Syn

be

divided by factors

of

the pump laser to the input BNC on the SDG II labeled

X" laser to pump your regenerative amplifier then

of2

,5, I 0 (see description

c"

to the input

CcoHEREnT.

10 CHAPTER3

2. Connect a BNC cable from the mode-locker "Sync" or "RF out" to the SDG II "RF Sync" BNC socket.

The other connections on the described below.

1.

Connect a BNC cable between the "Output I" on the SDG II and t Pockets cell driver in your regenerative amplifier.

2. Connect a BNC cable between the Pockels cell driver in your regenerative amplifier.

3. The

SDG II is now connected for regenerative amplifier operation. Refer to the appropriate section

the manual for optimization

SDG II rear panel are not necessary for normal operation. Their function is

he

BNC connector

"Output 2"

of

the adjustable outputs for regenerative amplification.

on

the SDG II and the BNC connector on the second

on

the first

3.1.2 Set-up for Photodiode Synchronization

Normally it is possible to operate the SDG II by synchronizing to the RF output In some cases however, for example when used with a unavailabl

This path conditions the signal via a the jumpers from the circuit board (labeled "50 Ohm Term. RF") on the circuit board ins ide the SDG II

near the

It

is necessary to "pick this beam. The photodiode will produce locked Ensure that the signal level, when viewed into a

e.

In this case it is necessary to use a photodiode to as the source for the synchronization signal.

50 Ohm termination. This termination can be switched

"RF sync" BNC connector.

off'

some

of

the light from the mode-locked laser beam. Place a fast photodiode

an

output that is a megahertz pulse train, similar to the mode-

la

ser optical output

of

course. First, look at this signal on a fast oscilloscope, 300MHz

pa

ssively mode-locked laser, this signal is

50

ohm termination , is 300mV or greater.

of

the mode-locked laser.

on

by removing

or

faster.

of

on

3.2 SDG

3.2.1 SDG

The SDG II has a "+ 5 VDC Enable" on the back which can be connected to an interloc

that when the triggers to the Pockels cells.

Another option availab

using as a seed source) with a photodiode rath

This is useful so that

photodiode will not provide the signal necessary to allow synchronizatio

the section above.

II

Detailed Description

II

Options

in

terlock is tripped, the output

le

with the SDG II is to synchronize the Oscillator (or mode-locked laser you are

if

the Oscillator stops mode locking, the synchronization is disabled since the

of

the regenerative amplifier is disabled by interrupting the

er

than the RF source provided by the Oscillator electronics.

n.

If

this option is used, then refer

C

COHEREnT

.

k,

for example, so

3.2.2 Front Panel Controls and Connections

SET -UP

AND

OPERA

TION

11

BWtl

Figure

3.1:

SDG

• • liiSIOP •

II

Front

SDG

Panel

• PO'

.

·

II

RESET

PO

7

s....:.r

10<0·

~

TRIGGER FREQUENCY READOUT: Displays the frequency

OUT

I I)EV.Y ns

of

the SDG II

's

output indicators.

INPUT DIVIDE: This adjustment allows the operator to divide the output frequency factor

of2

, 5, and 10.

SYNC ENABLE: This switch selects synchronized or un-synchronized mode illuminated the synchronization is enabled.

or

eliminated that the LED turns

the modelocked locked laser has stopped mode locking. Pressing the sync enable button so

off

will correct the error condition but it will also disable the synchronization portion

If

the error light

is

illuminated, then the sync source has been

of

operation,

the SDG II.

ERROR: This LED will illuminate when the SDG II is in the synchronized mode and the sync signal

SYNC is absent.

of

the SDG

SYNC

OUT

II

by

a

if the LED is

Da.AY

of

,,

BWD: This

into the stretcher so that the

interruption the trigger outputs being disabled. state.

LED proper alignment

can be overridden

on the back panel

is

the bandwidth detection part

LED's

PD l and PD 2 can illuminate when the reset button is pressed. Any

of

the beam alignment in the stretcher wi

Pressing the reset button should return the

If they

do

not

illuminate, the modelocked source characteristics

's

will illuminate only after the reset button has been pressed; they will not illuminate as a result

of

the beam onto the photodiodes without iteratively pressing the reset button.

(not

recommended)

ofthe

SDG ll.

of

the SDG II. The modelocked source beam must be aligned

ll

by turning the

cause eith

BWD

er

or

both

LED's

to tum

LED's

to their illuminated

or

alignment have changed. The

off. The on/off is controlled

off

by a toggle switch

, resulting in

The

of

a

BWD

MODE: This allows the user to select between continuous repetition rate firing (based on input trigger) and

single shot firing.

MAN TRIG: This is the single shot control when the

button

in

this mode will cause the three output triggers to fire a single shot.

ENABLE: These three switches enable or disables the 3 adjustable outputs, it dose n

TRIGGER

LED

's

are on, the outputs are enabled.

OUT

1 DELAY ns: All adjustable outputs function identically so for simplicity, discuss ion will be on one

The

illuminated LED indicat

OUT: on the rear panel.

es

the mode

If

the respective LED

of

operation.

MODE selected in SINGLE SHOT. Pressi

ot

effect the fixed

's

are off, the outputs are disabled and

ng

if

this

the

output only.

DELAY READOUT: Displays the selected delay

in

nanoseconds for its corresponding output.

CcoHEREnT

•

.

12 CHAPTER3

DELAY ADJUST: Adjusts the corresponding outputs delay in 1 ns steps, or 10 ns steps when the adjust

pu

knob is

shed in while adjusting. The adjustable range is 0 ns to 12

7S

ns ..

3.2.3 Back Panel Controls and Connections

ME1!1.0CK

Figure 3.2: SDG II Rear Panel

:

..

&

ll0Y.

2&

ON

RS-232

!!F

SYNC

EIIABI.t

IRICGE!!

~

&v

DC

IN

INTERLOCK ENABLE: This switch enables +5V

DC

connector is nonfunctional,

DC

+SV will disable all the adjustable outputs when the switch is open. Grounding the center pin enable operation.

TRIGGER OUT: is a fixed output. results in this TRIGGER

SDG II.

EXT TRIGGER: Apply the trigger source to this connector. The trigger source should be

RF SYNC: Apply the synchronization 1

BWD the up position. The switch in the down position disables the BWD (not recommended).

SERIAL PORT: Allows RS232 connection for control and programming using ASCII terminal software (see description below).

HIGH VOLTAGE: both HSD's

110/220 V AC: Fused primary power input for the SDG II, incorporated in this module is EMI protection, 1/2 Amp fuse and an on/off switch.

ENABLE: This connection allows the operator

OUT before the signal is sent to the three adjustable outputs on the front

OOMHz

into

son.

A jumper inside

ON: the BWD circuit is activated when the 4 pin 12mm connector is connected and the switch

HVl

(High Speed Driver).

in

The

of

and HV2 are 0-6kV

or

disables the +SVDC connector. In the up position the

the down position the connector is functional.

to

connect an interlock switch to the SDG II that

of

the BNC will

input pulse trigger to the SDG II goes through a one-shot that

son,

TTL

signal to this connector. The

the SDG II should be removed

DC

outputs. These are connected and used to power both

rf

source should be >

if

the

rf

source is not

of

the SDG II via a computer

lOOmV,

son.

of

0-

the

is

in

C

COHEREnT

•

SET-UP

AND

OPERATION

13

3.3 SDG

Most functions SDG II command syntax

panel

ofthe

II

Computer Interface

of

the SDG II can be controlled

is

designed

SDG II.

by

any computer with a standard RS-232 serial port. The

to

replicate the functions

of

the controls and read-outs on the front

3.3.1 RS-232 Connector Wiring

The

SDG II serial port accepts a standard 9-pin D-sub male/female extension cable for hookup. Only three

pins

on

the are used for serial communications:

Pin Number

2

3

5

Function

SDG

II

transmit data, computer receive data

SDG

II

receive data, computer transmit data

Signal ground

3.3.2 RS-232 Communication Protocols

The SDG II uses the following communication protocols, which must be set accordingly in the

communications program used to control the

SDG II.

Setting Value

Rate 9600 bps Data bits Parity None Stop Bits 1 Flow Control None

8

3.3.3 Command/Query/Response Format

All SDG II RS-232 commands, queries, and responses are in ASCII format. Each command

be terminated with a carriage return <CR>. Commands that have a numerical argument be sent with all the digits, preceded with zeros

question mark(?). Valid queries return data followed

the string

" Ok". Invalid commands or queries return the string "Bad".

if

necessary. Commands must be sent in all lowercase. All queries end with a

by

a carriage return <CR>. Valid commands return

or

query must

of

CcoHEREnT.

14 CHAPTER3

3.3.4 Command Quick Reference

Command Parameter Function

status? none Returns overall status set:cN # read:cN? set:del:cN read:del:cN? set: rate read :rate? read :bwd? none Returns the state

reset:bwd none read:sta :bwd? set:rf # read:rf? set:mode # read :mode? man:trig <none>

####

0, 1 Enable (1) or disable (0) output on channel N (1-3) none

.# 0000.0 to 9999.9 Set the delay for channel N (1-3)

none Returns the delay

0001 , 0002, etc. Sets the trigger rate division factor

none Returns the trigger rate division factor

none Read the state 0, 1 none Returns the state 0,

1

none

Returns

Reset the

Enable (1) or disable

Set Returns the state Manually trigger the SDG

the

output state

BWD

the trigger mode to continuous (0)

of

SDG

of

channel N (1-

for

channel N (1-3)

of

the

BWD

latching interlock

of

the

BWD

photodiodes

(0) the RF sync

of

the

RF

sync

of

the trigger mode

II

in single-shot mode

II

(see below)

inns

3)

or

single-shot (1)

3.3.5 Full Command Description

status?

set:cN #

Returns the status

li

sted

in

the

Parameter

Output 1 state

Output 2 state

Sync

Out state

Output 1 delay

Output 2 delay

Out

Sync

Trigger division factor

BWD BWD

Interlock state Continuous/Single shot RF Sync state

delay

Switch state photodiode & Ext

ofthe

following

SDG

table:

II

as a comma-delimited

# of Characters

1

6

4

1

3

1

list

of

eleven parameters. These values are

Value

0 (OFF) or 1 (ON)

0 (OFF) 0 (OFF)

0000.0

0000.0 ns to 9999.7 ns 0001 to 0010 0 (OFF) 000

0 (continuous) or 1 (single shot) 0 (OFF)

or

1 (ON)

or

1 (ON)

ns to 9999.7 ns ns

to 9999.7 ns

or

1 (ON)

to

111

(see below under read:sta:bwd?)

or

1 (ON)

Sets

the output

or disabled (0).

of

channel N (N=l

for

Out

l , N=2

for

Out

2, N=3

for

Sync Out) to be enabled (1)

read:cN?

Read the output state

(1) or disabled (0). The output state is also displayed by corresponding LED on the

SET-UP

of

channel N (N= 1 for Out 1, N=2 for Out 2, N=3 for Sync Out) as enabled

AND

OPERATION 15

fro

nt panel.

set:del:cN

read:del:cN?

set:rate

read:rate?

read:bwd?

####

Set the delay The minimum increment for the decimal) are other that 0,2,5,7 are rounded down to allowed values.

Returns the delay setting for channel N (N= l for allowed values for the last digit (after the decimal) are 0, 2, 5, and 7, corresponding to 0.00, 0.25,

0.50, and 0.75 ns respectively.

####

Sets the factor by which the input trigger fre quency (rep rate) is di vided to produce the output trigger frequency. A

rep rate is

Returns the input/output frequency divisor set by the set:rate command.

Returns the state

.#

of

channel N (N=l for Out 1, N=2 for Out 2, N=3 for Sync Out)

SDG II is 0.25 ns. The allowed val ues for the last

0, 2, 5, and 7, corresponding to 0.00, 0.25, 0.50, and 0.75 ns respectively. Last digits

Out 1, N=2 for Out 2, N=3 for Sync Out). The

ll

owed values are 0001, 0002, 0005 and 0010.

1.000 kHz, a rate

(0 = off, 1 = on)

of

0005 wi ll set the output frequency to 0.200 kH

of

the

BWD

mechanical switch

For

on

the back

in

example,

z.

of

nanoseconds (ns).

digit (after the

if

the input trigger

the SDG II.

reset:bwd

Resets the BWD latching int and

PD 2) are illuminated, reset:bwd will clear the BWD latching interlock.

off

, reset: bwd will clear the BWD latching interlock regardless

photodiodes.

read:sta:bwd?

Returns a string

off

, 1 = on). The third value is the state

example,

preventing output.

set:rf

#

Sets the state

read:rf?

Returns the state

of

three binary values. The first two values are the states

"

11

0" indicates that

of

the RF sync to be enabled

of

the RF sync as enabled (1)

er

lock.

If

the

BWD

switch is on and both

of

the +5V DC interlock (0 = latched, I = clear). For

PD

1 and PO 2 are illuminated but the +5V DC interlock is latched,

(I)

or

disabled (0).

or

disabled (0).

C

COHEREnT

.

of

the state

BWD

photodiodes (PD 1

If

the BWD switch is

of

the BWD

of

PD I and PD 2 (0 =

16 CHAPTER3

set:mode #

Sets the output trigger mode to continuous (0) or single-shot (1).

read:mode?

Returns the output trigger mode as continuous

man :trig

Executes a single output event when the SDG II is in single-shot mod

3.3.6 Limitations

Th

e following functions

• The value in the Trigger Frequency display cannot be read.

•

The

status

• The state set by the

• The state set by the Interlo

of

RS-232 Control

of

the SDG II cannot currently be accessed with RS-232 commands:

of

the Sync Enable Error LED cannot be read.

BWD

on/off mechanical switch cannot be changed.

ck

enable/disable mechanical switch cannot

(0) or single-shot

of

the SDG

3.3.7 Typical Command Usage

The following list gives a simple control flow for the SDG

um

on

1. T

the system, then wait >5 seconds for the SDG II in initialize.

(1

).

e.

II

be

II

using RS-232 commands.

changed.

2. Issue a status? command to determine the state

3. Enable the required outputs with the

set: eN commands; set the required delay values with

of

set: del: eN commands; set output trigger frequency with the s

ue

4. If all interlocks are cleared, iss

by

5. Monitor the SDG II

peri odica

a reset: bwd command

ll

y issuing a statu

C

COHEREnT

the SDG II.

to

enable output.

s?

command.

.

et.-,.a

te command.

th

e

4 Regenerative Amplifier Alignment

Th

is chapter is provided as a guide to regenerative amplifier alignment and operation. Coherent makes no

re

pr

esentation, or warranty as to wheth

damage occurs to your amplifier Coherent

er

this procedure will be applicable to your amplifier layout.

is

not responsible.

If

17

any

4.1

If complete alignment. Do not attempt this procedure before consulting a Coherent or Coherent representative.

1.

2. The beam should now be centered through each optical element in the resonator.

3.

4. Open up both apertures.

Static Regenerative Amplifier Alignment

you have real difficulty getting the regenerative amplifier to lase then, you will have to perform a

Set up the helium neon laser and two turning mirrors so that the beam can be aligned down the regenerative amplifier resonator, starting at the second that the beam easily accomplished by partially closing both intra-cavity irises so that the helium neon beam can be referenced to them.

piece

of through the optic. HeNe spot is close to an edge optic in the beam or refer to critical optical elements

If

all optical elements appear to be properly aligned, adjust the left-end high reflector to reflect the HeNe beam back along its path through both partially closed irises. Repeat this for the r ight-end high reflector.

is

aligned parallel to the optical bench and at a height

white paper in front

Using a small inspection mirror look through the end opposite the paper.

(Pockels cell, crystal, etc.).

of

the optic to be inspected, so as to block the HeNe beam from passing

of

the optical surface loosen the optical element mount and center the

fo

llowing sections which provide more detail for proper alignment

Pockels cell end

of2

of

the resonator.

Yz

inches above it. This

To

verify this, place a

It

is important

is

If

the

of

the

5. Follow the procedure described alignment

of

the regenerative amplifier.

in

the "Lasing Optimization" beginning

CcoHEREn

T.

of

this chapter to complete the

18 CHAPTER4

4.1.1 Pockels Cell Alignment

Use white paper to see apertures

Housed inside the along the beam. The cell must be tilted about two axes to achieve this (see below), the ha

s these adjustments

Use a piece you can view the beam on it. scatter the beam through the cell.

ofthe

of

white paper or card and place it in the beam about 3 inches beyond the Pockels cell so that

if

the beam is propagating directly through the center

Pockels cell (PC2).

Pockels cell

on

it.

is

a KD*P crystal.

TOP

Place a piece

If

it does not the Pockels cell must relocated.

It

is necessary to align the optic axis

VIEW

Figure

4.1: Pockels cell

oflens

tissue in the beam directly in front

adjustments

SIDE VIEW

of

the input and output

of

the KD*P crystal

Pockels cell mount

of

the Pockels cell to

It is necessary to view the beam through crossed polarizers. HeNe beam immediately after the

The pattern shown above represents a perfectly aligned Pockets cell, the spot beam.

l . Remove the lens tissue etc. from the beam path.

at

any point prior to the Pockels cell. P lace a second piece

Pockels. You will see a pattern like this

Figure

You will need to adjust the Pockels cell tilt, in both axes, to center the pattern on the beam.

4.2: HeNe

pattern

following

Place a piece

on

the white paper:

correctly

of

polarizing film in the beam

aligned Pockels ce

sheet polarizing film in the

ll

in

the center being the HeNe

C COHEREnT.

REGENERATIVE AMPLIFIER ALIGNMENT 19

of

2. Check the beam height at the end or

lowered the beam,

if

so then readjust the beam.

the resonator (near M2). The Pockels cell may have slightly raised

4.1.2 Polarizer Alignment

1.

The thin film polarizer is mounted in a housing which places the polarizer at the correct angle provided that the mount which holds the housing

possible.

off

2. Look at the HeNe reflection set screw which holds the polarizer housing

reflection is at

2.5".

the polarizer and

is

placed as close to perpendicular to the optical cavity as

mea

sure the beam height.

in

the mount and rotate the polarizer housing until the

If

it is not 2.5", loosen the

3. Verify that the beam passing through the polarizer and translate it. Repeat step

1.

is

not clipped.

If

it

is, loosen the polarizer mount

4.1.3 Laser Rod Alignment

1.

If

a crystal requires replacement, remove the two screws holding the top bottom mount and remove the top mount. Carefully remove and replace the crystal. Replace the top mount but do not tighten the screws.

or

2. Rotate the crystal until the reflected HeNe beam ( tighten the two top screws making sure the reflection remains at

3. The crystal front face is set at Brewster's angle at the factory. As long as the bottom crystal mount assembly has not been adjusted, no realignment should be necessary. rotated then Brewster's angle

(60 degrees) should be reset.

low energy pump beam)

2.5".

ofthe

crystal mount

is

at 2.5". Carefully

If

the bottom mount has been

to

the

4.1.4 Mirror Alignment

1.

Make a small hole

1'

about passes directly through the hole. Note that there may be reflections from other surfaces on the resonator that could be deceiving- a white card placed directly between the mirror and pinhole will block these reflection difficult to see because reflection will appear close Make small adju

(30cm) from the first resonator mirror. There should be a back reflection onto the paper that

in

the sheet

s.

When the mirror is well aligned the back reflection from the mirror will be

it

passes through the hol

to

st

ments to the X

of

white paper (about 1-2mrn diameter). Place this in the HeNe beam

e.

If

the mirror is not well aligned then the back

the hole. (You will be able to see this best with the lights dimmed).

andY

adjustments to center the back reflection on the hole.

2. Repeat this process for the other resonator mirror. In this case the best position for the paper is between the laser head and the second Pockels cel

cell which will

3. The static optical alignment is now complete, however it is a good idea to leave the HeNe aligned until you have completed the active alignment.

be

confusing. In this case you must determine which is the correct reflection.

l.

There will be several reflections from the polarizer

CcoHEREnT.

20 CHAP

TER4

4.2 Lasing Optimization

This procedure assumes that the regenerative amplifier oscillator is lasing, but requires complete

optimi

za

tion.

If

the regenerative amplifier oscillator is not las ing then it may be necessary to follow the static alignment procedure outlined below. "Daily Optimization" procedure in the preceding chapter.

Do not attempt to seed the regenerative amplifier with

t.

To

do

a Q-switched laser firs

this block the seed beam while completing the procedure below.

Prior to attempted this procedure it is advisable to follow the

the cw

laser beam yet. Operation must be ve rified as

WARNING!

All personnel

operating.

The regenerative amplifier is a laser which acts as an amplifier when a subnanosecond pulse greater than the intracavity noise level is inj ected into the resonator. Hence to ensure alignment regenerative amplifier

seed pulse:

Ml

within

I

the

laser

room

Even

small

energies

Goggles

A I

should

is

optimized, the regenerative amplifier can be operated as a laser in the absence

PC I

WPI

1

I D

T

Pump

beam

Ml,

M2 Resonator mirror

AI Aperture

WPl Broadband waveplate

PCl

, PC2 Pockets Cell

must

wear

from a pulsed

be

worn

of

INP

UT

L

Rl

at

laser

lea

e

Ll

laser

st

O.D. 4

protective eye

system

can

cause

to

all

lasing wavelengths.

OUTPUT

~

J

Rl

Ti:Sapphire Laser Rod

Pl

Broadband polarizer

Pump beam lens

L 1

wear

........

P I

at

all times

permanent

D

PC2

that

eye

of

I

M2

the

laser

damage.

intensity

of

the

of

is

a

Figure 4.3:

Optical

schematic,

CcoHEREnT.

regenerative

amplifier