以激光外差探测中两束光的特性为基础, 分析了相干光场和多模热光场的光子统计模型。分别讨论了上述两种光场的二阶和三阶统计特征, 其中二阶统计对应于Fano因子, 三阶统计对应于对称因子。对上述两种光场的Fano因子和对称因子进行了实验测量。结果显示, 相干光场的Fano因子和对称因子不随入射光子数而变化。将理论模型和实验数据相结合可得到与之对应的串扰概率为0.032 1, 探测器增益系数为1.046 0 ph。多模热光场的Fano因子随着入射光子数增加呈直线上升趋势; 目标运动速度加快, Fano因子逐渐减小, 表示回波光子波动减小, 认为其本质原因是热模个数增加引起的平均效应; 而多模热光场的对称因子呈抛物线趋势逐渐增加。对相干和多模热光场统计特性的研究, 为光子计数体制激光外差探测奠定了基础。

On the basis of the properties of two beams in heterodyne detection, the photon statistical models for the coherent light and multi-mode thermal light fields were analyzed. The second and third order statistical characters of the two kinds of optical fields were discussed, in which the second order statistics was corresponding to the Fano factor, while the third order one was to the symmetry parameter. The Fano factor and the symmetry parameter for the two kinds of light fields were measured experimentally. The results indicate that Fano factor and symmetry parameter do not change with the variance of incident photons for the coherent light field. Combined with the theoretical model and experimental data, it shows that the cross-talk probability is 0.032 1 and the gain coefficient is 1.0460 ph. However, the Fano factor of multi-mode thermal light field increases with the incident photons and gives a linear ascending trend. The factor reduces with the increase of the target velocity, which means the fluctuation of the echo photons decreases because of the averaging effect caused by increasing the number of thermal modes. Moreover, the symmetry parameter of multi-mode thermal light field is parabolic curve distribution. The research of coherent and multi-mode thermal light statistics provides a foundation for the laser heterodyne detection based on photon counting.