Pseudo-random single photon counting: Absolute rangefinding without alaising

Data acquisition systems and single photon sensitive detectors have made significant progress during the past decade ensuring that time correlated single photon counting (TCSPC) remains a viable technique likely to displace analogue detection for low light level lidar and time-of-flight (TOF) rangefinding. The time correlation is defined by the fixed time interval between the emission of the laser pulse and the detection of the retuned photon. The uncertainty in the measurement is limited by the jitter in the system, in particular, detector jitter. Since a repetitive pulse train is used the absolute range can be determined only within the interpulse time interval defined by the inverse of the pulse repetition frequency. This limits both the maximum absolute range that can be measured and the count rate leading to long exposure or dwell times and limited precision. The problem is exacerbated by solar background which reduces the signal-to-noise. However, a random pulse train can alleviate these problems by relaxing the constraint of a fixed time correlation leading to high speed photon counting. This extends the use of TCSPC to ranging on moving targets and imaging at low light levels. This paper presents theoretical results of a pseudorandom photon counting system and discusses the effect of atmospheric turbulence on the measurement of TOF.