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We describe the research and development of a scannerless three-dimensional (3-D) imaging laser radar (ladar) performed at the Army Research Laboratory for reconnaissance applications. Range information is obtained by a frequency modulation/continuous wave (FMJcw) radar technique implemented by amplitude modulation of a near-JR diode laser with an ifsubcarrier that is linearly frequency modulated. The diode's output is projected to floodlight the downrange image area.The returned signal is focused onto the cathode ofan image intensifier tube (lIT) where it is mixed with a delayed replica of the laser modulation applied to the cathode bias to modulate the tube gain. The output image of the lIT is modulated at an intermediate frequency (IF) that is sampled in time by a conventional charge-coupled device (CCD) camera. Image frames over one period ofthe frequency modulation are collected and stored. A discrete Fourier transfonn is calculated over the IF waveform to establish the ranges to all scatterers in a pixel. This processing scheme yields a scannerless ladar possessing high range resolution with no range ambiguities. We constructed a breadboard version ofthis ladar and used it to collect 256x 256 pixel images of targets at 1km ranges with 0.375-rn range resolution. We present imagery collected during field experiments and discuss the direction offuture research to enhance the ladar's perfonnance.

We report on the fabrication and characterization of interdigitated fmger, optical detectors/mixers. These devices are used in an FM/cw ladar system to detect and demodulate low intensity amplitude-modulated optical signals. Three different types of interdigitated fmger structure were tested and compared in this study. We also present a theory to explain the asymmetry observed in the devices and discuss its implication in an FMIcw ladar application