Model 421 Ultra High Vacuum Photodiode Detector
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The Model 421 Photodiode Detector is a fixed, ultra high vacuum, bakeable, windowless, photodiode detector. It is capable of detecting radiation at wavelengths shorter than 150-nm. Quantum efficiencies are 10% at 58-nm and 6% at 121-nm and 30-nm. However, the use of coatings such as MgF2 can produce yields approaching 40% at 58 and 30-nm. The useful photocathode diameter is 20-mm.
The diode is mounted on a 2-3/4" outer diameter metal seal flange with ceramic to metal electrical feedthroughs (MHV bayonet types) and can be baked to 400-degrees C. As an option it can be provided mounted to a 5" diameter 'McPherson' flange with 4-1/2" bolt circle to fit directly to McPherson vacuum and extreme ultraviolet monochromator exit slits.
The cathode is demountable to allow cleaning or for overcoating with any desired material.
The National Institute of Standards and Technology (NIST) has a working program for calibration of similar detectors. They have posted some typical response and parameter data on line.
References:
"Photocathodes: Their Efficiency and Stability" by James A. R. Samson - Nuclear Instruments and Methods in Physics Research 222 (1984) 215-220
"Metal Photocathodes as Secondary Standards for Absolute Intensity Measurements in the Vacuum Ultraviolet" by R. B. Cairns and J. A. R. Samson - Jurnal of the Optical Society of America, Vol 56, No 11, 1568-1573 (1966)