Scanning of low signature targets using time-correlated single-photon counting

We describe a scanning time-of-flight system which uses the time-correlated single photon-counting technique to produce three-dimensional depth images of scenes using low average laser power levels (ie <1mW). The technique is fundamentally flexible: the trade-off between the integrated number of counts (or acquisition time) against depth resolution permits use in a diverse range of applications. The inherent time gating of the technique, used in conjunction with spatial and spectral filtering, permits operation under high ambient light conditions.Our optical system uses a galvanometer mirror pair to scan the laser excitation over the scene and to direct the collected scattered photon return to an individual silicon single-photon avalanche diode detector. The system uses a picosecond pulsed diode laser at a wavelength of 850nm at MHz repetition rates. The source is directed to the target and the scattered return is collected using a 200mm focal length camera lens. The optical system is housed in a compact customdesigned slotted baseplate optomechanical platform. Currently, the system is capable of a spatial resolution and a depth resolution of better than 10cm at 1km range. We present a series of measurements on a range of non-cooperative target objects. © 2009 SPIE.