Chapter 7 Tips; Counter The Effects Of Aging; Maximize Throughput By Choosing The Right Vacuum Window Coating - Princeton Instruments ProEM+ EMCCD User Manual

Tips

Counter the Effects of Aging

EM gain can degrade over time, especially when large gain is used under high-light-level
conditions. The ProEM+ utilizes many anti-aging measures, including clock-voltage
optimization. Deep cooling allows the camera's high-voltage clocks to be operated well
below their maximum rating while still achieving greater than 1000x EM gain.
Despite the anti-aging measure built into the ProEM, some general precautions are
helpful in further countering the effect of aging:

Use the minimum required EM gain for a given light level. For example, only ~50x -
100x gain is needed to achieve <1 e- RMS read noise. Once <1 e- RMS effective
read noise is achieved, there will be no further improvement in signal-to-noise ratio
for most applications.

Turn down the EM gain to 1x when used with bright light sources.

Use maximum gain only when there is a need to amplify single-photon events above
the background for the purpose of thresholding.
Maximize Throughput by Choosing the Right Vacuum Window
Coating
To maximize light throughput, the ProEM+ uses a highly advanced single-window
vacuum design. This means the vacuum window is the only optical surface encountered
by incident photons before they reach the EMCCD detection surface. Although the
design is the best available, each uncoated optical surface of the vacuum window can still
have 3.5% to 4% transmission loss, or a total loss of 7% to 8%. For light-starved imaging
applications, this loss can result in a significant reduction of signal-to-noise ratio.
Moreover, any light reflected inside the system can lead to glare and fringing, especially
when used with coherent illumination. The solution is to apply anti-reflective coatings on
the window in the optical path, which reduces total losses to below 1% and sometimes
even to 0.5%.
All Princeton Instruments cameras, including the ProEM, are designed with a single
window made of high-grade fused silica/quartz that acts as a vacuum viewport. Any
shipping-protection windows on the EMCCD are removed prior to installing it in the
vacuum chamber. The vacuum window can be customized with single- or multi-layer AR
coatings to match the wavelength of interest. Customers should note that AR coatings
typically provide the best performance when they are tuned for a narrow wavelength
range. Since they may have poorer transmission outside their optimum wavelength range,
care must be taken before choosing an AR coating. Princeton Instruments representatives
can help you select the most appropriate AR coating for your application needs.
Chapter 7
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