Space operation and performance of doped germanium photo-conducting detectors in the far infrared: Experience from the ISO LWS

The performance of the ten doped germanium photoconducting detectors on the Infrared Space Observatory Long Wavelength Spectrometer is discussed. This instrument was designed to make spectroscopic measurements of astronomical sources in the wavelength range from 43 to 198 mu m. It employed* a combination of stressed and unstressed Ge:Ga detectors and one Ge:Be detector coupled to Infrared Labs JF-4 integrating amplifiers. The performance of the detectors was affected by the ionising radiation in the space environment. The Noise Equivalent Power of the detectors increased by a factor of similar to 4 compared to that measured during ground testing. We show that this was the result of reducing the operating bias, and therefore the responsivity, of the detectors and using shorter integration ramps to alleviate the effects of the ionising radiation impacts.