Kilometer range depth imaging using time-correlated single-photon counting

Active depth imaging approaches have numerous potential applications in a number of disciplines, including environmental sensing, manufacturing and defense. The high sensitivity and picosecond timing resolution of the single-photon counting technique can provide distinct advantages in the trade-offs between required illumination power, range, depth resolution, and data acquisition durations. These considerations must also address requirements for eye-safety, especially in applications requiring outdoor, kilometer range sensing. We present a scanning time-of-flight imager based on high repetition-rate (>MHz) pulsed illumination and a silicon single-photon detector. In advanced photon-counting experiments, we have employed the system for unambiguous range resolution at several kilometer target distance, multiple-surface resolution based on adaptive algorithms, and a cumulative data acquisition method that facilitates detector characterization and evaluation. We consider a range of optical design configurations and discuss the performance trade-offs in more detail. Much of this work has been performed at wavelengths around 850nm for convenient use with Si-based single photon avalanche diode detectors, however we will also discuss the performance at wavelengths around 1550 nm employing superconducting nanowire single photon detectors. The extension of this depth profiling technique to longer wavelengths will lead to relaxed eye safety requirements, reduced solar background levels and improvements in atmospheric transmission.