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3. Low light level sensors
For night-time imaging, the very low levels of illumination encountered mean that sensors must be much more sensitive and less noisy than those designed for daytime use, and historically based on photoconduction: photoemission by a photocathode naturally seemed to be the only possible solution. The introduction and ongoing improvement of solid-state circuits now make it possible to exploit the very high quantum efficiency of photodiodes, and pave the way for new low-light devices.
But let's start with vacuum devices featuring a photocathode:
A photocathode is a layer of material which, when placed in a vacuum, emits electrons when it receives light. In the absence of an electric field, these electrons fall back onto the layer. In the presence of an electric field, they can be accelerated, and possibly multiplied, to form a brighter image,...
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Low light level sensors
Bibliography
In Engineering Techniques
Directory
Manufacturers - Suppliers
This list is not exhaustive.
Tubes vidicon
Narragansett imaging http://www.nimaging.com/products/
CCD arrays and matrices
Dalsa Inc. http://www.dalsa.com
e2v...
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The Ultimate Scientific and Technical Reference