Evaluation of a solid state photomultiplier focal plane array in the U.S. Army Strategic Defense Command CALM facility

Evaluation of a solid state photomultiplier focal plane arrayin the U.S. Army Strategic Defense Command CALM facilityCarl F. DadsonRockwell International CorporationAnaheim, CaliforniaABSTRACTThe U.S. Army Strategic Defense Command facility for the Characterization of AdvancedLow-Background Mosaics (CALM) is operated by Rockwell International Corporation. The facilitysupports a cryogenic test chamber with controlled background (flood) and target sources. The testchamber allows the measurement of focal plane array response to a moving point image in the presence ofa radiant background that may be controlled over a range from less than 1O to over i014photons/second-square centimeter. An ancillary data acquisition system is capable of performing a15-bit, analog-to-digital conversion of focal plane array output data and storing processed digital data at2 megabytes per second. This paper describes the facility and its use in the evaluation of a solid statephotomultiplier (SSPM) focal plane array. The SSPM is a back illuminated, impurity band conductiondevice capable of detecting individual photons over infrared wavelengths extending from 1 to 28micrometers. A description of the test configuration, test conduct, and data analysis are presented alongwith results of the SSPM evaluation.1. INTRODUCTIONThe United States Army Strategic Defense Command provides a test capability to support development ofthe optical sensors and components required to fulfill its role in the requirements of the Strategic DefenseInitiative. The capability includes the CALM facility for the Characterization of AdvancedLow-Background Mosaics (Focal Plane Arrays).1 The CALM facility is designed to support radiometrictesting of devices ranging from single chip design to large arrays with filters and on-array signalprocessing. The CALM chamber provides a low radiant background and a target source that can irradiateeach detector element within a complex array. This unique combination of capabilities is ideally suitedfor the evaluation of the Solid State Photomultiplier.The solid state hotomultiplier (SSPM) is a development of the Rockwell International CorporationScience Center.' The SSPM is an impurity band conduction (IBC) device capable of detecting individualphotons over infrared wavelengths extending from 1 to 28 micrometers. While the IBC device isessentially a reverse biased photodiode, the SSPM functions as an avalanche device. The SSPM employs ahigh reverse bias, resulting in electron gain through the impact ionization of neutral impurity atoms. Theoutput from an SSPM detector is an electron charge packet, ultimately produced by the detection of asingle photon. Both the remarkable sensitivity of the SSPM and the discrete nature of its output- -chargepacket in lieu of the continuous current- -requires a test design much different than that required forevaluation of the typical infrared detector.This paper describes the CALM facility, the SSPM detector and the design of the interface electronicsrequired for evaluation of this novel device. Evaluation of the SSPM requires techniques not normallypart of the evaluation of the typical infrared detector. The unusual aspects of test conduct are describedalong with the methods used in the reduction of the test data. This paper also includes the results of theSSPM characterization: quantum efficiency, dark response, nonlinearity and cross talk.