光电倍增管输出电子流脉冲堆叠对光子计数法测距的影响

Effect of pile-up of electron flow pulse from photomultiplier tube on ranging by photon counting

光电倍增管(photomultiplier tubes,PMT)具有光子级别的灵敏度、低暗计数、低后脉冲概率,被广泛应用于可见光波段的光子计数雷达中.PMT没有光子探测死区时间,每响应一个光子就会输出一个电子流脉冲,这些电子流脉冲有可能堆成规模更大的脉冲,使用阈值鉴别法鉴别光子事件时,堆叠的脉冲会引入额外的脉冲行走误差.考虑到脉冲堆叠的影响,建立了新的PMT光子探测理论模型,并通过蒙特卡罗仿真,得到了基于PMT的光子计数测距法的行走误差、测距精度和回波激光脉宽,PMT输出电子流脉宽以及光子事件鉴别阈值之间的关系.搭建了基于PMT的激光雷达系统,通过与GM-APD的对比实验证明了脉冲堆叠对PMT光子计数法测距存在不可忽略的影响.考虑到脉冲堆叠的PMT光子探测模型能够指导基于PMT的光子计数雷达的设计,提高测距系统的测距精度和准度.

Photomultiplier tube(PMT)features single photon level sensitivity,low dark count,and low afterpulse probability,and are widely used in photon-counting lidar in the visible spectrum.The PMT has no photon detection dead time,for every photon it responds to,it can output an electron flow pulse,these pulses of electron flow are likely to pile up into larger pulses.When using threshold identification method to identify photon-events,the stacked pulse will introduce additional pulse walking error,directly affecting the ranging precision of photon-counting ranging method in the practical application of laser ranging.Considering the influence of pulse pile-up,a new theoretical model of PMT photon detection is established to describe the influence of pulse pile-up on the detection probability of photon-events by analyzing the relationship between the detection time of photon and the identification time of the PMT final output photon-events.Through Monte Carlo simulation,the relationship among the ranging walking error,ranging accuracy,incident laser pulse width,PMT output electron flow pulse width and photon-events identification threshold is obtained.In order to verify the correctness of the theory,a PMT-based photon-counting lidar system is built.The comparative experiment with GM-APD proves that the influence of pulse pile-up on PMT photon-counting ranging method cannot be ignored,and that the experimental results are in good agreement with results from the theoretical model.The PMT photon detection model based on pulse pile-up can guide the design of PMT photon-counting radar and improve the ranging accuracy and precision of the ranging system.