Interceptor Seekers

A radiation-hard, 1064-nm sensitive, single-photon-sensitive avalanche photodiode (APD) detector with photon detection efficiency (PDE) and dark count rate (DCR) superior to state-of-the-art Geiger-mode APDs, and with two orders of magnitude faster maximum count rate (MCR) will be developed. Geiger APDs are constrained by a fundamental tradeoff between DCR and MCR: if the APD is cooled to reduce DCR, then its dead time must increase to avoid afterpulsing, thereby reducing MCR. Linear APDs are not subject to this constraint, and so can be operated with dead times on the order of 250 ps. This improvement in MCR translates into a proportional improvement in single photon bit rate. Voxtel has previously demonstrated a multi-stage InGaAs APD design with high gain and low avalanche noise. In this effort, the dark count rate of the multi-stage APD will be improved by using InGaAsP gain stages to replace the existing oxygen-scavenging InAlAs materials. The improved multi-stage APDs will be demonstrated to have high gain (>1,000), low jitter (<20 ps), high saturation (>108 photon), and with low DCR (< 10 kHz) at temperatures >220 K, so that in Phase II, fully functional 32 × 32 LADAR arrays can fabricated and demonstrated.