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Chapter 9
Tips and Tricks
Introduction
In Chapters 4 and 6, the objective was to show how to take an image or spectrum with a
minimal operating configuration and following a simple procedure. In this chapter, we
consider factors that affect more complex measurements.
Overexposure Protection
Image intensified detectors such as the PI-MAX3 can be destroyed if exposed to
excessive light levels. Princeton Instruments cannot take responsibility for damage due to
misuse.
Intensified detectors must not be continuously exposed to high-level radiation ( 10
-4
foot candles). When the illumination level is not quantitatively known, toggle the I.I.T.
switch (on the back of the PI-MAX) to the OFF position while you are adjusting the
incoming light level. After making adjustments, toggle the switch to the ON position. If
the alarm sounds repetitively, toggle the switch back to OFF and readjust the lighting
conditions.
If the experimental conditions dictate that only a small portion of the photocathode is
illuminated over relatively long periods of time, change the illuminated region of the
photocathode periodically to avoid long term localized photocathode or MCP damage.
If you can do so, it is a good idea to avoid intense light on the intensifier even when it is
off. High light levels increase EBI, often for hours, even when the intensifier is off.
Image burn-in can occur with some photocathode types.
Note: The audible alarm and protection circuits are not fail-safe protection, particularly
when working with high intensity sources such as lasers. For additional information, see
the “Alarm” discussion on page 54.
Signal Delay
Introduction
For the detector to see a transient signal, it is essential that it be gated on when the signal
arrives at the detector. If this requirement isn’t given careful consideration, it is possible
to set up an experiment in which the signal will come and go before the detector is gated
on. If this happens, no proper data can be taken. Depending on the nature of the
experiment and the specific equipment involved, a number of different factors may need
to be considered to be assured that the detector gates at the right time.
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