134 PI-MAX/PI-MAX2 System Manual Version 5.F
b. Now select the Gating tab. If the experiment can use the same gate width
and delay for both frames, then select Repetitive, and click on the Setup
button to set the appropriate gate width and delay. If the experiment requires
different gate widths or delays for each frame, then select Sequential and
click on the Setup button to set the appropriate gate widths and delays. The
number of images should be set to 2, the gate width and delay for the first
frame should be set as the starting values, and the width and delay for the
second frame should be set as the ending values.
c. At the bottom of the Pulser Setup dialog, click OK to download the gating
sequence to the PTG.
5. The CCD parameters need to be set to the appropriate values for DIF operation.
Select Experiment Setup from the Acquisition menu.
a. On the Timing tab, select Dual Trig. Mode.
b. On the Main tab, verify that the Number of Images is 2 and the Intensifier is
in Gate Mode.
c. When the experiment is ready, click the Acquire button to start the image
acquisition.
Tips and Tricks
Experiments using the DIF feature of the PI-MAX2 can be complex, and timing of the
events is usually rather exacting. Here are several points to consider that may make the
experiment setup or troubleshooting much smoother and easier.
The most important piece of equipment in a DIF experiment is an oscilloscope.
The PI-MAX2 has a Gate Monitor signal on the back of the camera head which
is very useful for seeing when the two image exposures occur during the course
of the experiment. The use of the Gate Monitor and an oscilloscope is discussed
in more detail in Chapter 11: Tips and Tricks.
The short time between the two images in DIF requires an intensifier with a fast
phosphor. P46 phosphor as a decay time of ~ 2 µs, that means it takes 2 µs for
the phosphor emission to drop to 10% of its peak value. The decay is not a
simple single exponential; even after 100 µs there may be 1% or more of the first
image on the phosphor screen. It is usually possible to subtract a percentage of
the first image from the second image to remove the residual image. If this is not
possible, there are intensifiers with P47 phosphor, which is an order of magnitude
faster than P46.
The software uses the Shutter Compensation Time to determine how long to wait
after the gate pulse to shift the image. This value can be adjusted in the Hardware
Setup dialog. If there is some residual image from the first frame in the second
frame, simply increase the Shutter Compensation Time to allow the phosphor
more time to decay before shifting the image. If residual image is not an issue,
then Shutter Compensation Time can be shortened to decrease the time between
the two DIF images.
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