ation of a CCD, some pixels show time fluctuations in the dark current with the appearance of random telegraph noise. These measurements were performed on an EEV imager at 10°C. The mean time constants for the high and low states increased at lower temperatures. After [Hopk93]. Despite the extreme sensitivity of CCDs to displacement damage, they are used successfully in space for many applications. Instrument shielding, CCD cooling, careful selection of device architecture and operating conditions, and signal processing all can be used to partially mitigate the proton induced performance degradation. Other types of two-dimensional sensor arrays, such as photodiode arrays, p-channel CCDs [Spra97] and active pixel sensor arrays show promise for future use in severe space environments. 3.3.3 Photodetectors Photodetectors are designed to collect photo-generated charge. Since particle- induced charge is also sensed, such devices are inherently radiation sensitive. Displacement damage causes an increase in the bulk dark current via carrier generation in depletion regions. Also, the degradation in minority carrier lifetime ( ) reduces the carrier diffusion length (L) in accordance with the well-known relation, L = (D ) 1/2 , where D is the diffusion constant. The result is degradation of the detector responsivity. Nevertheless, adroit selection of components and good system design permits their successful use in a proton environment. For example in data link and encoder IV-87 applications, the radiation induced increases in dark current and the reduced responsivity can be accommodated in the optical power link margin [Mars92, Mars94]. The radiation response of many types of detectors has been investigated, including pn junction photodiodes [Soda75, Wicz82, Barn86, Kord89], p-i-n diodes, phototransistors [e.g., Soda75, John96, Reed98], avalanche photodiodes (APDs) [Buch95, Sun97], multi-quantum well infrared photodetectors (MQWIPs) [Khan96], etc. Detectors that depend on the minority carrier lifetime and diffusion limite