Eye-safe laser radar focal plane array for three-dimensional imaging

Previous efforts to develop 3-D laser radar (ladar) imagers have required multiple laser pulses and complex stable scanning and timing systems in order to generate images. This paper describes the progress that has been made in program developing an approach that will enable a complete 3-D ladar image (angle-angle-range) to be captured with a single pulse. It has been previously reported that a unique processor chip was designed and fabricated that was intended to be bump bonded directly behind a detector array, the sensor provides separate independent range finder circuitry for each pixel. The time-of-flight for each pixel is recorded on the chip and the values are then read out serially. This approach allows the range resolution to be determined by the laser pulse width and electronics bandwidth and to be independent of image framing rates. The original version of this concept is a 32 X 32-pixel device. A silicon photo-diode array was bonded to the processor chip. This limited the useful wavelength of the sensor 1 micron and below. Images generated using this sensor will be presented. The effects of shot-to-shot fluctuations, turbulence and scintillation on image quality will be discussed. The next generation, under development at this time, will also be presented. This sensor will be a 64 X 64-pixel device. The detectors will be electron-capture anode plates and the device will be sealed into an image intensifier tube. The photocathode material will be InGaAs, engineered to be sensitive to 1.5 microns. Results from the photocathode development effort, including quantum efficiency and micro-channel plate gain will be presented.