Princeton PI-MAX2 User Manual

PI-MAX2 DIF Camera

Introduction

This technical note assumes a basic understanding of the operation of the PI-MAX2 and
PTG in Gate Mode using WinView or WinSpec. Please refer to Chapter 7 of the
PI-MAX/PI-MAX2 system manual if you do not feel confident with the basic operation

of the PI-MAX and PTG in Gate mode.

The purpose of the PI-MAX2 DIF system is to acquire a pair of gated images in rapid
succession. The time between frames can be as short as 2 µs with exposure times as short
as 5 ns. The DIF capability is ideally suited to capturing rapidly evolving events. These
experiments will fall into one of two broadly applicable categories: single trigger and
dual trigger experiments. Single trigger experiments involve a single impulse event that
evolves over time such as a laser-induced plasma or luminescence decay. Dual trigger
experiments involve two impulses separated in time such as double laser pulse
velocimetry measurements.

Requirements

The following requirements must be met for DIF operation:

(Dual Image Feature)

•

the PI-MAX2 must use an interline CCD,

•

the controller must have a High Speed PCI Interface (TAXI) board and a PTG
board installed, and

•

the entire system must be set up for DIF operation at the factory.

In addition to these requirements, it is recommended that the intensifier have a fast decay
phosphor (P46 or P47). Since DIF operation involves acquiring images in rapid
succession, phosphor persistence can become the limiting factor in the rate of image
acquisition.

WinView or WinSpec software (version 2.5.16 or later) can control the DIF functionality
of the PI-MAX2 and provides full access to the two DIF timing modes: single trigger and
dual trigger.

Interline CCD Operation

An interline CCD consists of alternating columns of light sensitive pixels and storage pixels.
The light sensitive columns are referred to as the active area and acquire the image. The
storage pixels are called the masked area and store the image in the dark while it is read out.
With this architecture, the CCD can acquire a second image while the first image is being
read out, unlike a standard CCD, which must read out the first image before the second
acquisition can begin. The ability of the interline CCD to quickly transfer an image under the
masked columns and hold it there makes DIF possible. As soon as the first image is acquired,

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PI-MAX2 DIF Camera

it is shifted under the masked area and held. The second exposure begins and is held in the
active area until the first image is read out.

Timing Modes

In WinView and WinSpec, the timing modes available in the

Setup…|Timing

tab are different from those in standard intensified systems. The

Acquisition|Experiment

available timing modes are:

Single Trig. Mode: two shot, one trigger for both shots.

Dual Trig. Mode: two shot, each shot requires a trigger.

The trigger(s) can be generated by an external source attached to the PTG or the PTG can
generate the trigger(s) internally. When using a PTG internal trigger, the experiment will
normally be triggered by a signal from the ST-133. Typically, the rising edge of T0, from
the PTG, is used.

Single Trigger Mode

The Single Trigger Mode only requires a single trigger to initiate the acquisition of both
images of the DIF operation. The Single Trigger Mode uses the Burst Mode feature of
the PTG to acquire two images from a single trigger event. On the

Gating

Pulse dialog, the Burst Mode should be turned on. The Number of Pulses must be set to
2, and the time between the images is set by the Burst Period. It is very important that the
Burst Period be large enough to accommodate the gate width, gate delay, and phosphor
decay time. To set the gate width and delay, select Repetitive Mode from the
of the Pulse dialog and then click on the Setup button.

Note: Sequential Mode will not create different gate width and delay for the two images
in Single Trigger Mode due to Burst Mode selection.

tab of the

Gating

tab

Trigger

Burst Period Burst Period

Intensifier Gate

SCAN

Shutter

CCD Operation

Gate

Delay

Burst Period ≥ Gate Delay + Gate Width + Shutter Comp.
Shutter Comp. = Phosphor Decay Time

Gate

Width

≥ Shutter

Comp.

400 ns

≥ 2 µs

Shutter Comp.

Shift
first image

Gate

Delay

Gate

Width

400 ns

Read out
both images

Figure 1. DIF Operation: Single Trigger Timing Diagram

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PI-MAX2 DIF Camera

Dual Trigger Mode

The Dual Trigger Mode requires two triggers to acquire both images of the DIF operation.
The PTG will control the gating of the intensifier for both images. To make the gate width
and delay the same for both images, select Repetitive Mode from the
Pulser dialog then click the Setup button to set the values. To make the gate width and delay
different for each pulse, select Sequential Mode from the
then click the Setup button to set the values. The Number of Images should be set to 2, and
the first image will use the starting values for gate width and delay while the second image
will use the ending values.

Trigger

Gating

Gating

tab of the Pulse dialog,

tab of the

Intensifier Gate

SCAN

Shutter

CCD Operation

Gate

Delay

Gate

Width

400 ns

Shift
first image

Shutter Comp. = Phosphor Decay Time

Gate

Delay

≥ 2 µs

Shutter Comp.

Gate

Width

Figure 2. DIF Operation: Dual Trigger Timing Diagram

400 ns

Read out
both images

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