【作者】 史久林；

【导师】 杨克成；

【作者基本信息】 华中科技大学 ， 物理电子学， 2013， 博士

【摘要】 受激布里渊散射（stimulated Brillouin scattering, SBS）作为非线性光学中的一个重要研究方向，有很长的研究历史，已被广泛应用于相位共轭、脉宽压缩、放大、慢光以及布里渊激光雷达海洋遥感探测中。然而，有关受激布里渊散射的一些基本特性仍然缺少相应的实验研究，比如温度依赖性。本论文主要围绕介质温度对受激布里渊散射特性的影响做了相关的研究，包括脉宽、线宽、阈值及增益系数等；并利用受激布里渊散射脉宽及线宽的温度依赖特性，实验测量水的体粘滞系数及水中的声速、温跃层；以及分析环境参数（温度、湿度、大气压强）对激光在水中传输时衰减系数的影响。布里渊散射的激光雷达系统目前已有几套比较成熟的系统装置，如：基于扫描法布里-珀罗干涉仪的布里渊激光雷达系统，基于边缘探测技术的探测系统等。这几套布里渊激光雷达系统有其自身的优点，但由于它们都是建立在自发布里渊散射的基础上，所以存在着一些不足之处，如散射信号弱并且有较强的信号串扰，降低了目标探测的分辨率。而受激布里渊散射具有很好的位相共轭特性，散射信号强度远远大于自发布里渊散射信号强度，所以基于受激布里渊散射的激光雷达系统能大幅度提高雷达的探测性能。其中，利用柱透镜和法布里-珀罗标准具及ICCD为主要探测器件的受激布里渊散射激光雷达系统，实现了散射光谱由环状谱到点状谱的变化，使得干涉条纹中每一级圆环上的能量集中到两个对称的点上，在相同回波信号强度下，大大提高了接收信号的强度和信噪比，从而提高了受激布里渊激光雷达系统的探测性能。脉宽、线宽、阈值及增益系数是布里渊散射的几个重要参数，目前的研究主要集中在室温条件下，而对于变温条件下的温度依赖特性，则缺少相应的实验研究。本论文主要从理论分析及实验结果两方面来介绍介质温度变化对受激布里渊散射的脉宽、线宽、阈值、增益系数等基本特性的影响。实验结果表明，受激布里渊散射脉宽随着温度的降低而变窄，温度越低脉宽压缩效应越明显，而受激布里渊散射线宽则随着温度的降低而变宽。受激布里渊散射阈值及增益系数也同样受介质温度变化的影响，随着温度的升高，阈值呈现指数下降趋势，而增益系数则呈现指数上升趋势。受激布里渊散射激光雷达研究的最终目的是用来进行实际的遥感探测。本论文在理论分析的基础上，介绍了基于受激布里渊散射的水中特征参数测量，包括声速、粘滞系数以及温跃层等。在对声速的测量研究中，给出了纯水及不同盐度海水中声速的理论计算值，在理论计算的基础上，实验测量了纯水及35‰盐度海水中的声速，实验测量值与理论计算值比较吻合。针对受激布里渊散射脉宽及线宽的温度特性，并根据线宽与脉宽成傅里叶变换的关系，提出了通过测量脉宽来计算线宽及测量水体粘滞系数的新方法。同时，详细介绍了利用受激布里渊散射测量水中温跃层的基本方法，并分析了温跃层的基本分布规律及特点，在实验测量的基础上，通过对热传导方程在特殊条件下的模拟分析，总结得出了温跃层分布的时间特性。为了进一步提高受激布里渊散射激光雷达的探测性能，本论文还研究了不同大气环境条件下532nm激光在水中的衰减系数。在同一地点实验测量时间跨度超过一年，实验结果显示大气环境对激光的衰减系数有着重要的影响。当气压高并且温度低时，激光在水中的衰减系数最小；当气压低并且温度高时，衰减系数最大，最大衰减系数值是最小衰减系数的三倍。最后讨论了衰减现象出现的物理机制，研究结果对分析水中声波的传输也具有重要意义。更多还原

【Abstract】 Stimulated Brillouin scattering (SBS) is an important subject in nonlinear optics, theresearch of SBS has a long history. SBS has been widely used in several applications,especially in phase conjugation, pulse duration compression, amplification, and slow ligh,even in Brillouin lidar for remote sensing of the ocean. However, some basic properties ofthe parameters of SBS have still been seldom studied experimentally, such as thetemperature dependence. In this thesis, the influence of temperature on the properties ofSBS (pulse duration, linewidth, threshold value and gain coefficient) has been investigated.Then, some parameters include sound velocity, bulk viscosity and thermocline weremeasured based on the temperature dependence of SBS. Moreover, the influence ofatmosphere environment (air pressure, air temperature and air humidity) on the attenuationcoefficient of light in water has been analyzed.Brillouin lidar system has been developed for a long period，there are some maturesystems，such as a Brillouin lidar based on Fabry-Perot scanning interferometer, and edgedetection technique, etc.. However, the lidar system based on spontaneous Brillouinscattering has some disadvantages in applications. The major problem is that thespontaneous signal is uncontrollable, and the crosstalk of signal from different depthsmakes a relatively low depth resolution in detecting. Compared with spontaneous scattering,SBS is easier to detect due to its phase conjugation property and strong scattering signal. So,the technique based on stimulated Brillouin scattering can improve the performance of lidarsystem greatly. In this paper, a SBS system which composed of cylinder lens, Fabry-Perotetalon and ICCD is made to boost the performance of lidar. Using this system, theinterference ring shaped by F-P etalon can be concentrated to two spots, therefore, thedetecting intensity and the signal-to-noise ratio (SNR) can be improved significantly.As the several important parameters, the pulse duration, line-width, threshold valueand gain coefficient of SBS, only the properties at room temperature were given for somematerials. It must be addressed that this temperature dependence is actually important, andhas great significance in applications. However, the temperature dependence of theseparameters is not clear now, even little work was reported. In this paper, the influence oftemperature on the properties of SBS has been investigated theoretically and experimentally. The results indicate that, the measured pulse duration of SBS decreases with the decrease oftemperature; the lower of the temperature is, the more obvious of the pulse compressioneffect is. The line-width of SBS increases with the decrease of temperature. Moreover, theresults also show that the threshold value of SBS decreases exponentially with an increaseof temperature, whereas the gain coefficient increases with the increase of temperature.The ultimate aim for developing the SBS lidar is used for remote sensing in ocean. Inthis paper, the measurement of underwater parameters (sound velocity, bulk viscosity andthermocline) based on SBS was conducted. In the study of sound velocity, the theoreticalvalues were given respectively in the pure water and seawater with different salinities.Based on the theoretical analysis, the sound velocities were measured respectively in thepure water and seawater with the salinity of35‰experimentally. Based on the temperaturedependence of pulse duration and line-width of SBS, this paper details a new method formeasuring the bulk viscosity of water which using the Fourier transform of pulse duration.Meanwhile, the measurement of thermocline in water has been done using SBS method.The distribution and features of the thermocline have been analyzed. On the basis ofexperiment, the time response of thermocline has been presented by simulating the thermalequation with some special conditions.In order to improve the detecting performance of SBS lidar, the attenuation coefficientof532nm light in water under different atmospheric conditions was investigated.Measurements were made over more one year period at the same location and show that theattenuation coefficient is significantly influenced by the atmospheric environment. It islowest when the atmospheric pressure is high and temperature is low, and is highest whenthe atmospheric pressure is low and temperature is high. The maximum attenuationcoefficient of pure water in these studies was about three times the minimum value. Themechanism of the phenomena is discussed. These results are also important in underwateracoustics.更多还原