Model 452 Vacuum Ultraviolet Polarization Analyzer
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The need to make polarization measurements in the vacuum ultraviolet (VUV) is growing with the use of synchrotrons, accelerators and various plasma sources for high-energy research, and lasers for excitation and analysis in the Extreme Ultraviolet and EUVL laser and other sources.
The Model 452 Vacuum Ultraviolet (VUV) Polarization analyzer and diode detector are well suited to operation in the 30 to 150-nm wavelength region. The unit operates by measuring reflectance of a gold coated optically flat mirror at 45-degrees to the incident radiation. This is accomplished by rotating a detector into the incident beam and then, into the reflected beam. The entire analyzer is rotated through 90-degrees while still under vacuum, and the measurements repeated. The degree of polarization of the incident radiation can be determined from the two reflectance measurements.
The detector is nominally an Aluminum photodiode that does not discriminate against the degree of polarization of the radiation. Other materials as MgF2 and Au can also be used to shift sensitivity. Silicon detectors could also be considered.
Advantages Si photodiodes have over tube type detectors are:
- Small size
- Ease in experimental implementation
- Insensitivity to minute surface contaminants and magnetic fields
- Ultrahigh vacuum and cryogenic compatibility
- A large dynamic range
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)