INTERFERENCE EFFECTS IN RETICON PHOTODIODE ARRAY DETECTORS

A detector system incorporating the Reticon RL1024S photodiode array has been constructed at the National Oceanic and Atmospheric Administration Aeronomy Laboratory as part of a double spectrograph to be used to study the Earth's atmosphere from ground-based and aircraft-based platforms. To determine accurately the abundances of atmospheric trace gases, this new system must be able to measure spectral absorptions as small as 0.02%. The detector, manufactured by EG&G Reticon, exhibits superior signal-to-noise characteristics at the light levels characteristic of scattered skylights, but interference in the passivating layer (a thin layer of SiO2 that is deposited during the manufacture to protect the silicon active area from water vapor) causes major problems in achieving the required precision. The mechanism of the problems and the solution we have implemented are described in detail.