Princeton Instruments PI-MAX 3 System, Manual, Page: 75 / 150

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Chapter 8
Dual Image Feature (DIF)
Introduction
The purpose of PI-MAX3 DIF is to acquire a pair of gated images in rapid succession.
The time between frames can be as short as 2 µs (limit imposed by P46 phosphor decay
time) 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 requirement must be met for DIF operation:

the PI-MAX3 must use an interline CCD,
In addition, it is recommended that the intensifier have a fast decay phosphor (P46).
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 2.5.26 or higher) can control the DIF
functionality of the PI-MAX3 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, 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.