Research On Detection Accuracy Improvement Method Of Photon Heterodyne Detection System

Laser heterodyne detection is a multidimensional detection method that can obtain target orientation,distance,intensity and velocity information,and has important applications in the field of target recognition.The linear APD detector used in traditional laser heterodyne detection has limited sensitivity,and it cannot work normally in the field of ultra-long distance detection and very weak signal detection.Photon heterodyne detection is a new detection technology that combines heterodyne detection technology with photon counting timing.By using Gm-APD with single photon detection capability as a detector,photon heterodyne detection sensitivity is greatly improved,but also Some problems,such as the fact that the local oscillator will overwhelm the IF signal and the frequency difference between the local oscillator and the echo,will come.Therefore,this dissertation focuses on the important index of photon heterodyne detection precision,studies the influencing factors that affect photon heterodyne detection accuracy,and seeks methods and means to improve photon heterodyne detection accuracy.The photon heterodyne detection technology is much higher than the direct detection method and its resolution is much higher,and since the photon heterodyne detection technology can detect echo signals with a weak to photon magnitude,the detection system's working distance is greatly improved.In this dissertation,the physical mechanism of photon heterodyne detection is first studied.Starting from the laser heterodyne detection theory and photon counting theory,a physical model of photon heterodyne detection is established,and then the photon heterodyne detection process is mathematically simulated.The law of time distribution of signal photons in the photon heterodyne detection process,the mapping law between photon heterodyne detection results and traditional heterodyne intermediate frequency signals are analyzed,and the theoretical basis for the spectral signal extraction of photon heterodyne signals is established.Focusing on the analysis of the photon heterodyne signal spectrum,the SNR is used as a criterion to analyze the system parameters of the photon heterodyne system,and the influence of the local oscillator on the SNR is studied.Three kinds of photon heterodyne signal spectrum analysis methods such as Fourier transform method,photon arrival time interval method,and window division method are studied.The digital signal output from the photon counter is converted into a traditional heterodyne IF signal processing method.The signal processing can greatly improve the detection accuracy.Using the optimized spectrum analysis method,the power spectral density of the photon time distribution with smaller line width can be obtained,the photon counting rate of the photon heterodyne detection system is analyzed,and the power spectral density analysis of the photon heterodyne detection system is completed.Optimize the important conditions for detection experiments and improve the signal-to-noise ratio of the system.By optimizing the local oscillator intensity and signal processing methods,a high signalto-noise ratio and a narrow line-width power spectral density are obtained to improve the system's detection accuracy.A photon heterodyne detection experiment system was set up to perform Doppler detection on moving targets,and system parameters were further optimized experimentally to complete the measurement of the velocity of uniform moving targets and variable-speed moving targets.The experimental data was processed by the proposed data processing method.The velocity of the uniform moving target was measured to be 1.0622 m/s,and the velocity error was 0.005 m/s.The speed of the variable speed target changes from 1.0622 m/s to 1.5940 m/s.The experimental results show that the photon heterodyne detection results for uniform moving targets are consistent with the uniform target.Finally,the extraction of micro-Doppler information for the acceleration target is completed,and the relatively clear target micro-Doppler spectrum is resolved.