基于光子时间间隔统计的激光相干频率分析新模型

The enhancement of detection sensitivity for traditionallaser heterodyne detection is mainly based on increasing the power of local oscillator,in fact,the higher the local oscillator, the intenser the short spot noise. Therefore,this scientific project will mainly solve the problem of large noise in coherent detection founded on photon counting.The detailed description of the research contained the following two aspects: Firstly, the local oscillator and the echo signal in coherent detection can be regarded as coherent and pseudo-thermal light field respectively. The Multi-Pixel Photon Counter(MPPC) can be used for photon statistics,the primary parameter which can be acquired from the statistic are as follows: the number of thermal modes for the light field, the Fano factor,symmetry parameter.The statistacal property of the mixed light field can be gained through the methods above.thereby, the research before will be the groundwork for the target's reflection characteristic and the frequency extraction of coherent detection.Secondly,the novel mode for the frequency extaction has been established through the statistic of arrived photon time interval,this new method is absolutely different from the traditional way of frequency analysis based on FFT(Fast Fourier Transform).The frequency extraction of the new method is based on the PDF (Probability Density Function) curve of the arrived photon time interval statistics,and the mixed efficiency of the echo signal and local oscillator can be given through the analysis of the PDF curve.In the course of theoretical and experimental research,the photon counting rate is far smaller than the medial- frequency of the two laser beams'interference,in this way ,we can detected higher interfered frequency through lower photon counting rate.The theoretic research showed that this new method can break through the dead time limitation for bandwidth of the MPPC detector.

传统激光相干探测依靠增加本振光束的功率来提高探测灵敏度，而实际研究中发现较强的本振光会带来较大散粒噪声。因此，该项目旨在从光子计数角度分析弱激光相干探测中存在的上述问题。具体从以下2方面展开研究：第一，采用多像素光子计数器(MPPC)作为接收探测器，将激光相干探测所需的本振光和信号光分别看作相干光场和赝热光场进行统计分析，主要分析参数包括光场热模数、Fano因子、对称参数，通过对上述两种光场分析获得混合光场统计特性，为分析目标反射特性及干涉信号频率提取提供数据支撑。第二，在混合光场干涉频率提取方式上，采用全新的光子时间间隔统计方式，建立光场干涉频率分析新模型，在其概率密度分布函数曲线上提取激光干涉信号频率，并进一步估计信号光和本振光的混合效率。其中所采用光子计数率远小于干涉信号频率值，即以较小的光子计数率探测较高干涉频率，理论分析表明，该方法能够突破MPPC死亡时间所带来的探测器带宽限制。

激光相干探测采用本振激光与回波光束干涉的方式，实现对回波信号的相干增强，因此具有高灵敏性和抗干扰能力强等优势，在远距离目标测距测速、跟踪成像以及近距离目标振动检测领域具有较多应用。传统激光相干探测依靠增加本振光束的功率来提高探测灵敏度，而实际研究中发现较强的本振光会带来较大散粒噪声。因此，该项目旨在从光子计数角度分析弱激光相干探测中存在的上述问题。具体从以下2方面展开研究：第一，采用多像素光子计数器(MPPC)作为接收探测器，将激光相干探测所需的本振光和信号光分别看作相干光场和赝热光场进行统计分析，主要分析参数包括光场热模数、Fano因子、对称参数，通过对上述两种光场分析获得混合光场统计特性，为分析目标反射特性及干涉信号频率提取提供数据支撑。第二，在混合光场干涉频率提取方式上，采用全新的光子时间间隔统计方式，建立光场干涉频率分析新模型，在其概率密度分布函数曲线上提取激光干涉信号频率，并进一步估计信号光和本振光的混合效率。其中所采用光子计数率远小于干涉信号频率值，即以较小的光子计数率探测较高干涉频率，理论分析表明，该方法能够突破MPPC死亡时间所带来的探测器带宽限制。研究结果表明，采用MPPC作为光子接收器件，能在一定程度上提高入射光子数动态范围，有利于控制本振光束入射强度，同时利用该器件的光子响应以及时间特性，可建立起基于光子到达时间间隔统计的激光相干频率分析模型，该模型可采用较小的光子计数率获得远大于它的干涉信号频率，从而突破MPPC器件死时间对接收带宽的限制，对相同的接收器件可实现更大频率范围的干涉信号解析。

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