光子计数激光外差探测及拍频信号频谱识别

	光子计数激光外差探测及拍频信号频谱识别
	刘立生
学位类型	博士
导师	郭劲
	2014-07
学位授予单位	中国科学院大学
学位专业	光学工程
摘要	激光外差探测在空间目标探测、伪装目标识别中广泛应用，相对于直接激光探测它有着探测灵敏度高、速度分辨率高等优势；最近十年美国林肯实验室将光子计数器引入到外差探测，实现了弱本振光、低散粒噪声外差信号探测。　　本论文主要讨论了两大方面内容：一是光子计数体制下激光外差探测，及对记录光子时间信号处理，从记录光子时间频谱密度分布和相邻光子时间间隔概率密度两个方面解析得到拍频频率；二是激光外差探测多类目标，对目标运动造成的回波信号多普勒频谱进行识别，获取目标的运动速度、转动目标的频谱展宽曲线、振动目标的二维频谱图像等目标运动信息。在这两个方面工作的基础上，对激光外差探测系统形成一个系统而完整的认识，对外差探测系统中多个技术环节进一步加深认识并形成一定的设计优化方案；在实验过程中对激光外差探测系统中噪声来源、光路系统布局、外差探测影响因素等均实现一定探索和认知。其工作内容详细如下：　　（1）介绍了激光外差探测基本理论基础、光子统计理论、外差信号光子时间频谱解析理论及外差系统激光传输信噪比分析。为后续实验工作开展提供了良好理论基础。　　（2）应用多像素单光子计数器（MPPC），实现对激光外差信号的探测及拍频频率解析。首先采用了频谱分析法，对记录光子时间进行快速傅里叶变换得到光子时间频谱密度分布，采取多数据段均值及归一化累乘两种方式得到最大拍频频率为1.04MHz的频谱峰值。然后采用统计的方式，创新性提出从相邻光子时间间隔满足的概率密度分布中解析拍频频率，得到6MHz、8MHz、10MHz和12MHz拍频频率，分析了探测频率上限问题，指出统计方式解析频率上限不受奈奎斯特采样定理限制，进一步实验解析得到80MHz拍频频率。　　（3）对激光外差探测系统做了详细分析，指出系统中存在的噪声源及提出一些解决方案，并探讨了激光相干长度（线宽）对外差探测的影响，指出外差探测距离远远大于激光相干长度时，在外差信号频谱上得到的峰值宽度为激光线宽2倍。在大量调研和实验的基础上形成了比较成熟的外差探测系统。　　（4）在前述外差系统优化设计的基础上实现了对运动点目标频谱识别，实现了对类简谐运动、转动目标高精度实时测速，并用带宽1MHz激光器实现了外场8.1km激光外差探测实验，验证激光相干长度对外差探测影响。提出采用伪随机序列码调制方式来提高外差探测探测概率的方案。　　（5）分析了转动二次曲面面目标后向反射信号在频谱上的展宽模型，并以实验的形式验证了转动圆锥体和圆柱体的展宽曲线，与理论相符良好。采用点扫描方式，对转动、振动目标进行扫描测量，形成二维空间-频谱图像，实现对目标轮廓信号的探测，该探测方式能够对强度成像难以识别的伪装目标进行探测。本论文实现了光子计数体制外差信号探测，在探测器上实现一定创新；综合分析了整个外差探测系统中所遇到的一些实际问题，并对提出了解决方案，实现目标频谱识别及二维频谱图像。通过理论推导并结合大量实验，对外差探测有了深刻认知，并为后续研究提供一些借鉴。
其他摘要	Laser heterodyne detection is widely used in the detection of space target and the discrimination of camouflaged target; Compared with the direct laser detection, it has the advantage of high detection sensitivity and high speed resolution. In recent ten years, Lincoln Laboratory has introduced the photon counter into heterodyne detection to achieve the weak local oscillator light, low shot noise heterodyne signal detection. 　　Two aspects of work are mainly discussed in this paper which are heterodyne detection with the photon counter and the discrimination of the frequency-spectrum of the beat signal. For the first aspect, heterodyne detection is conducted using photon counter; the beat frequency is derived by two methods, one is by frequency spectrum density distribution of the recording photons time and the other is by the probability density distribution of successive photons time-interval. For the second aspect, types of targets are detected by laser heterodyne detection, the retro-reflection signal’s Doppler frequency spectrum is identified which is caused by the movement of the targets, the moving information such as the speed, frequency-spectrum broadening of rotation, two-dimension frequency-spectrum imaging of vibration are derived. Based on the work of the two aspects, we form a complete understanding of laser heterodyne detection system, deeply explore of number of techniques, and give an optimization design project of the system. In the experiment, we analyze the noise source, the optical setup, the influence factor and so on. The detail work contents are as follows: 　　(1) We introduce the basic theory of laser heterodyne detection and photon statistics, and the analytical theory to derive the photon time frequency-spectrum of heterodyne signal; also analyze the Signal-to-noise ratio of the laser transmission. All the work provides a good theoretical basis for the experiment in the subsequent section. 　　(2) A multi-pixel single photon counter (MPPC) is used to detect the laser heterodyne signal and to get the beat frequency. In the first method, the frequency spectrum analysis is used in which a fast Fourier transform is conducted on the photon arrival time of the beat signal to get the frequency spectrum density distribution. With next process, sets of frequency spectrum density distribution are averaged or multiplied together after normalized to obtain a maximum frequency peak of 1.04MHz. In the second method, the probability density distribution (PDF) of successive photons time-interval is derived, and in the experimental PDF curve we achieve the beat frequencies of 6MHz, 8MHz, 10MHz and 12MHz. We give an analysis of the upper limit of the frequency the method can derive, and point out that the upper frequency is not limited by the Nyquist criterion, and then the frequency of 80MHz is derived in the further experiment. 　　(3) Based on the detailed analysis of the heterodyne laser detection system, we point out the source of noise and propose the solutions. The effect of the laser coherent length on the heterodyne detection is investigated with the conclusion that when the range of laser transmission is far larger than the laser coherent length, the peak frequency in the frequency spectrum density distribution is broadened to about 2 times of the laser frequency line width. A relatively mature heterodyne detection system is formed based on large number of research and experiment work. 　　(4) Based on the optimized design system, we achieve the frequency spectrum identification of moving point target which include the high-resolution real-time velocity measurement of the harmonic motion and rotation, and achieve the successful detection experiment of cooperative target in the range of 8.1km which test the effect of laser coherent length on laser heterodyne detection. We propose a detection scheme to improve the detection probability in which a modulation is conducted on the frequency of transmitted laser and local oscillation using the pseudo-random sequence code. 　　(5) We analyze the model of the reflected laser signal frequency-spectrum broadening for the quadric surface targets in rotation, and the theory is verified by the experiment in which the rotating cone and cylinder is detected using scanning point by point, the frequency-spectrum broadening curve is in consistent with the theory well. The rotating and vibrating targets are detected by point scanning, and the two-dimensional space-frequency-spectrum image is formed which could be used to detect the target profile. The technique can identify the camouflage target which the intensity image could not. In this paper, we achieve heterodyne detection with single photon counter which is an innovation in the detector; and give a comprehensive analysis of a number of practical problems encountered in the heterodyne detection system resulting in some optimization solutions for the impact factor; the frequency spectrum identification and 2D spectrum image is achieved. The paper provides a deep understanding of the laser heterodyne detection system by combination of the theoretical analysis and experiment and provides some inference for the further study.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/41437
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	刘立生. 光子计数激光外差探测及拍频信号频谱识别[D]. 中国科学院大学,2014.

条目包含的文件
文件名称/大小	文献类型	版本类型	开放类型	使用许可
刘立生.pdf（6100KB）			开放获取	CC BY-NC-SA	请求全文