Advanced infrared detectors for multimode active and passive imaging applications

Abstract

Active systems, using a near-infrared pulse laser and a fast, gated detector, are now adopted for most long range imaging applications. This concept is often called laser-gated imaging (LGI) or burst-illumination LIDAR (BIL). The SELEX solid state detector is based on an array of HgCdTe avalanche photodiodes, and a custom-designed CMOS multiplexer to perform the fast gating and photon signal capture. This paper describes two recent developments. The first is aimed at reducing the size, weight, power and cost of steerable platforms which often have to contain a large number of electrooptic tools such as lasers, range finders, BIL, thermal imaging and visible cameras. A dual-mode infrared detector has been developed with the aim of shrinking the system to one camera. The detector can be switched to operate as a passive thermal imager, a laser-gated imager or a solar flux imager. The detector produces a sensitivity in the MW thermal band of 16-18mK and a sensitivity in the BIL mode as low as 10 photons rms, in other words close to the performance of dedicated imagers. A second development was to extend the current BIL capability to 3D. In complex scenes, with camouflage and concealment, the ability to generate 3D images provides a signal-to-clutter advantage. Also in airborne applications, especially, it is useful to have 3D information to provide agile, feedback control of the range gating in a dynamic environment. This report describes the development of the 3D detector and camera, and the results of field trials using a prototype system.