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 germaniumphotoconducting detectors on the Infrared SpaceObservatory Long Wavelength Spectrometer is discussed. This instrument was designed to make spectroscopicmeasurements of astronomical sources in the wavelengthrange from 43 to 198 m. It employed^* a combination of stressed and unstressed Ge:Ga detectorsand one Ge:Be detector coupled to Infrared Labs JF-4integrating amplifiers. The performance of thedetectors was affected by the ionising radiation inthe space environment. The Noise Equivalent Power ofthe detectors increased by a factor of 4 compared tothat measured during ground testing. We show thatthis was the result of reducing the operating bias,and therefore the responsivity, of the detectors andusing shorter integration ramps to alleviate theeffects of the ionising radiation impacts. ^ast ISO exhausted its helium supply on 8 April 1998.