Photon Counting Chirped Am Ladar: Concept, Simulation, and Experimental Results

The operating principles and experimental results for the Army Research Laboratory's (ARL's) patented chirped amplitude modulation (AM) ladar using linear response detectors have been presented and published previously, and will be briefly summarized here (Stann, et. al., 1996). In ARL's current prototypes using unity gain detectors, amplifier noise limits the receiver sensitivity. This noise is well above the signal shot noise limit. We are developing a method using Geiger-mode avalanche photodiode (Gm-APD) photon counting detectors in the chirped AM ladar receiver to yield sensitivities approaching the shot noise limit. Such sensitivities represent about four orders-of-magnitude improvement over the sensitivities of the currently used unity-gain, opto-electronic mixing (OEM) metal-semiconductormetal (MSM) detectors. The sensitivity improvement demonstrated by the photon counting chirped AM ladar experiments may enable very compact, low power, eye-safe, and/or long range ladars with low cost, low bandwidth readout integrated circuits (ROICs).