This research will substantially advance the state of the art in single-chip photodetector arrays. Advanced Photonix, Inc. manufactures unique large-area, single-element silicon avalanche photodiodes (currently 16mm active-area diameter,but potentially up to 75mm). The research will demonstrate feasibility (Phase I) and produce a prototype (Phase II) of such a photodetector subdivided into an array of individually isolated "pixels". Each 1x1mm(2) pixel will have a gain of 1000 and a noise equivalent power (NEP) of 2x10(-15) W/Hz(1/2) at 800nm - about a factor of twenty better than conventional (gain=1) silicon photodetectors of the same pixel area. This innovation will permit breakthroughs in strategic defense applications, including the imaging laser radars in "brilliant" antimissile interceptors. Breakthroughs will also be possible in civilian applications, such as Positron Emission Tomography (PET) scanning, and optical fiber readout of high energy physics detectors.