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Kestrel/USER-MANUAL/REV1.1/08-20
9. CONTROLLING THE CAMERA (XCAP)
The sections below will give information on using each control of the Kestrel, giving a
description on how to use each control parameter and their effect on the camera’s
performance. The software used to illustrate the camera controls is XCAP.
9.1 EM Gain
The EM gain applied can be controlled from the
“Gain”
tab of the XCAP GUI, shown in
Figure 6. The user can either manually input a value to apply EM Gain or use the slider bar
provided. By default, the EM Gain slider bar is set to zero (Gain = 1).
The values in the EM Gain slider bar on XCAP are not real/linear gain values. More detailed
information on why Raptor does not calibrate “real gain” controls can be seen from the
“Understanding Electron Multiplying Gain”
technical note from our website:
https://www.raptorphotonics.com/products/kestrel-emccd/
The values on XCAP are the DAC (Digital to Analog Converter) values. During the
calibration of the camera, the DAC value vs EM Gain ratio is characterized and stored in
memory locations of the camera. The slider is directly controlling the amount of voltage that
the EM gain register in the camera is seeing. The relationship of gain to the DAC value is
exponential, so up until around 3000 on the slider, there is a minimal gain being applied
(roughly in the region of 1-10x). Once you go above 3000, as the gain ramps exponentially,
small changes in the slider will equate to larger changes in the gain. A gain of X1000 should
be achievable by setting a DAC value of roughly 3500, as long as the camera is water
cooled to roughly -20
ͦ
C. There isn’t any real benefit to using a gain larger than this. For
most applications, a gain in the region of X200 is sufficient.
Please note that EM gain should only ever be used when it is required and leaving the
EM gain running indefinitely may cause irreparable damage to the camera. EM Gain
should only be used during the experimental test. If the camera is in idle mode and
not being used, EM Gain should be disabled. Extreme caution must be used when
setting the DAC value for the EM Gain. As the relationship between the DAC value and
gain is exponential, DAC values greater than 3000 result in large changes of real gain
being applied. Using gains in the upper region (3500 – 4096) for longer lengths of time
will cause the sensor to age and could cause damage to the camera.
Figure 6: EM Gain.
