A compact 3D imaging laser radar system using Geiger-mode APD arrays: system and measurements

MIT Lincoln Laboratory continues the development of novel high-resolution 3D imaging laser radar technology and sensor systems. The sensor system described in detail here uses a passively Q-switched solid-state frequency-doubled Nd:YAG laser to transmit short laser pulses (similar to 700 ps FWHM) at 532 rim wavelength and derive the range to target surface element by measuring the time-of-flight for each pixel. The single photoelectron detection efficiency has been measured to be > 20 % using these Silicon Geiger-mode APDs at room temperature. The pulse out of the detector is used to stop a > 500 MHz digital clock integrated within the focal-plane array. With appropriate optics, the 3202 array of digital time values represents a 3D spatial image frame of the scene. Successive image frames from the multi-kilohertz pulse repetition rate laser pulses are accumulated into range histograms to provide 3D volume and intensity information. In this paper, we report on a prototype sensor system, which has recently been developed using new 32x32 arrays of Geiger-mode APDs with 0.35 mum CMOS digital timing circuits at each pixel. Here we describe the sensor system development and present recent measurements of laboratory test data and field imagery.