Laser Ranging By Photon-number-resolving Detection

Long-range laser ranging technology generally based on time-of-flight method. The distance of non-cooperation target was detected by measuring round-trip time of laser pulse travelling between emission point and the target. This technology has been extensively applied in the field of ladar and industrial measurement. When Single-photon Detection and Time-Correlated Single Photon Counting (TCSPC) technologies were both applied to the laser ranging system, the detection sensitivity was increased to the limit of single photon, which greatly improved the detection rang of the system. In this paper, sensitive laser ranging was demonstrated at few-photon level by using photon-number-resolving detection.The application of single photon detector can improve the sensitivity of laser ranging system enormously, but due to the nonlinearity of the photon detection process, the echo signal is treated as a digital signal and the intensity of the signal can only acquired and analyzed by accumulated measurement for a long time. We introduced the photon-number resolving detection technology and realized a laser ranging system based on multi-pixel photon counter (MPPC). In this system,the photon number of echo signal were directly measured and the arrival time was measured by the TCSPC to get the distance information.The system integrated a Q-switched laser@532nm, TCSPC, as well as a photon-number resolving detector. The precision of time detection was about550ps and the photon number of echo pulse was convert by the ADC module. In the experiment, a458m-away non-cooperation target was successfully detected under2.5×1031x sunlight by adjusting the photon detection threshold. When the detector threshold was set at5photon/pulse, the system error count rate dropped from3.3X106counts/sec to2.2×105counts/sec, greatly reducing the interference caused by the background light and dark noise. Under laboratory circumstance, using a single laser pulse energy of0.4nJ, two targets of different surface reflection coefficient were distinguished in32m-distance, providing an advantage in remote surface imaging at few-photon level. Photon-number-resolving detectors facilitated remote laser ranging at few-photon level with the similar capabilities of linear optical detectors but much higher sensitivity.