Chapter 1 Introduction 19
Summary of PI-MAX Data Acquisition
Figure 2. Major Components of the Intensifier-CCD
In the PI-MAX camera, the input image is focused onto the photocathode of an image
intensifier tube. The tube electronically amplifies the image and outputs it, much brighter,
as gray-scaled green light. That light is then coupled to the CCD using a fused fiber-optic
bundle from the output of the image intensifier to the front side of the CCD window. The
image at the output of the image intensifier is translated to the input of the CCD at the same
size.
*
After being detected by the CCD, the image is read out to the Controller, where it is
digitized and transferred to the computer for processing via a high-speed data link.
The sequence below steps through the process by which photons are converted to data
that can be displayed on a computer monitor. For the sake of simplicity, triggers and gate
pulses are not mentioned and it is assumed that a PCI interface card is installed in the
host computer. When reading through the sequence, keep in mind that electrons are
attracted to more positively charged surfaces and are repelled by more negatively charged
surfaces. This principal is used to control electron flow through the intensifier tube:
changing the photocathode voltage with respect to the voltage at the MCP input is used to
switch (gate) the intensifier on and off.
1. Incident photons pass through the intensifier input window, strike the photocathode,
and release electrons. (See Figure 2 above.)
2. Assuming that the intensifier is gated ON (the photocathode is more negative than the
MCP input), these electrons will be attracted to the MCP input. Gating acts like a
shutter in that gating the intensifier on allows the CCD to "see" light and gating the
intensifier off prevents the CCD from seeing light.
*
Units having a tapered fiber optic bundle may also be available. Contact the factory for
information.
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