International Radiation Detectors, Inc.

AXUV Photodiode Applications

The AXUV photodiodes have several advantages over the orthodox tube-type XUV detectors. The AXUV photodiodes exhibit very low noise, do not need external voltages for their operation, are insensitive to magnetic fields, cost less to fabricate, have low mass and have large collection area to size ratio making them extremely attractive for use in satellites and deep space probes.

These diodes have been approved as transfer standards in the XUV spectral range because of their ease of use, excellent stability and spatial homogeneity of quantum efficiency, large dynamic range (over eight orders of magnitude), small size, ruggedness, and ultrahigh vacuum compatibility. These diodes are operated in the open face configuration down to Angstrom wavelengths, even in the presence of gases. This feature gives the AXUV diode based spectrometers an important advantage over present XUV spectrometers based on conventional detectors, which need to be used either in vacuum or with a window.

Due to these unique features, AXUV photodiodes have been successfully used in the European SOHO and Coronas-Photon, and American SNOE, SORCE, GOES, TIMED and EOS solar space instrumentation.

An AXUV multi-element diode array has been successfully used in a Ring Accelerator Experiment (RACE) at Lawrence Livermore National Laboratory and also by other fusion research laboratories around the world to obtain radiated power vs. length and radius profiles of the plasma. Owing to its fast response speed, the array was found to yield excellent time resolution of power in quasisteady plasma transients.

Small active area AXUV diodes optimized for high response speed were found to be ideal detectors for XUV measurements in a joint US/Russian magnetized target fusion experiment. The performance of the AXUV diodes tested was found to be comparable with that of diamond detectors with orders of magnitude lower cost.

Several quadrant AXUV diodes with central holes and rectangular slit openings have been built specifically for synchrotron beam intensity monitoring and position sensing. Because of its 5 micron physical silicon thickness, the AXUV36 diode can be used in transmission mode for continuous intensity monitoring of the x-ray beam. These devices have proven to be very useful since the unstable nature of synchrotron radiation beam is an important source of experimental error.