International Radiation Detectors, Inc.

Amplifier for the AXUV Series Photodiodes
(MODEL # AXUV-100 HYB1/HYBV)

General purpose electrometers are extremely sensitive instruments used in the measurement of current generated by the photodiodes. They are commonly used with the AXUV series photodiodes around a synchrotron light source. However, the relatively large size of many commercial electrometers make it difficult to locate them close to the detector. The long interconnecting cables can pick up significant amounts of noise from electromagnetic interference and from mechanical vibration. This problem has been noticed by scientists from several laboratories as evident from the recent literature on the detector/amplifier combinations [1,2]. Reference [1] reports a silicon diode/operational amplifier combination with noise performance comparable with photomultiplier tubes and avalanche photodiodes! Scientists at NIST have demonstrated 14 decades of photocurrent at room temperature using low noise operational amplifiers [2]

The AXUV-100 HYB1 is a high vacuum compatible current to voltage converting amplifier that was developed specifically for use with the AXUV-100, AXUV-20, UVG-100 and UVG-20 photodiodes. The combination of the detector/amplifier hybrid can be used to measure small photogenerated currents with a resolution of 10 fA and a dynamic range of four orders of magnitude. The dynamic range is much more for the AXUV-100 HYBV because the fixed 10 G-ohm of feedback resistor in AXUV100HYB1 can be changed in this device.

Fig. 1: The AXUV-100HYB1 Amplifier

Fig. 2 AXUV-100HYB1 electrical schematic

References:

[1] R. J. Fonck et.al.
"Low Noise Photodiode Detector for Optical Fluctuation Diagnostics"
Rev. of Sci. Instr. Vol. 63, P. 4924-4926 (1992)

[2] G. Eppeldauer and J. E Hardis
"Fourteen-decade Photocurrent Measurement with Large - area Silicon Photodiodes at Room Temperature"
Appl. Optics, Vol. 30, 3091-3099 (1991)