【作者】 刘瑞；

【导师】 王雨雷；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2016， 硕士

【摘要】 在激光与物质相互作用而产生散射的过程中,受激拉曼散射(SRS)与受激布里渊散射(SBS)共同竞争泵浦光的能量,近年来已经成为重要的研究课题。对于常用液体介质,在单纵模激光器泵浦时,受激布里渊散射会在竞争中占据绝对优势,这是由于受激布里渊散射的稳态增益远大于受激拉曼散射的前后向增益,而使得受激拉曼散射被抑制所致。但是随着泵浦光能量的增加,受激拉曼散射的强度会呈指数形式增长,而在高功率激光器中由于泵浦功率密度较大,受激拉曼散射成为不能被忽略的因素,这会使得受激布里渊散射的能量反射率下降、泵浦光的光束质量变差而可能导致光学元件损伤。本论文对受激布里渊散射中的受激拉曼散射现象的研究主要以以下步骤进行:SBS和SRS的基本概念和经典电磁学理论的分析以及推导;宽带激光泵浦下,针对小拉曼频移介质的前向SRS增益系数测量方案的设计及实验;一种有效的SRS抑制方法的设计与实验验证。首先,分别从SBS与SRS的经典电磁理论出发,分析了SBS与SRS在与物质相互作用过程,得到了SBS稳态和瞬态状况下的振动方程、SRS泵浦光和Stokes光的耦合方程、SRS稳态和瞬态的增益等结果。然后,根据理论的结果,确认了从SRS增益系数入手研究SBS与SRS关系的方案:以宽带激光(532nm,Nd:YAG锁模激光器)作为光源,利用注入介质产生的前向SRS经过滤光与泵浦光的相互作用(两束光同轴同向并且脉冲波形峰值重合)对产生的一阶Stokes光进行放大,最后利用分光法将一阶Stokes分离,测量放大前后一阶Stokes的光强、泵浦光光强、泵浦光和Stokes光时空重叠的有效面积和脉宽,通过简化计算得到该介质的SRS增益系数。并依据实验结果对比分析了重氟碳系列材料作为SBS介质的优劣。最后,通过理论分析,设计了的能够抑制SRS的方案,具体做法是在与激光相互作用的介质中插入色分离镜,利用此方法在700MW/cm2的泵浦下,其前向SRS效应降低了2.88倍,此方法结构简单,可以在介质中反复应用多次以进一步降低其中的SRS现象。更多还原

【Abstract】 In the process of interaction between laser and materials resulting in producing scattering, stimulated Raman scattering(SRS) and stimulated Brillouin scattering(SBS) contend the energy of the pump, it has been an important research topic in recent years.In common used liquid medium, stimulated Brillouin scattering dominates when pumped by single longitudinal mode laser due to the steady state gain of st imulated Brillouin scattering is much higher than that in forward and backward stimulated Raman scattering, and stimulated Raman scattering is suppressed. However, with the increase of pump energy, stimulated Raman scattering will form of exponential growt h. In high power lasers, due to the high pump power density, stimulated Raman scattering become the factors that can not be ignored, it will lead to the reflectivity of stimulated Brillouin scattering energy down, beam quality variation of the pump and may lead to damage optical element.This thesis of stimulated Brillouin scattering of stimulated Raman scattering phenomenon research mainly in the following steps: the basic concept of SBS and SRS and classical electromagnetism theoretical analysis and deduction; in broadband laser pump, the design and experiment of forward SRS gain coefficient measurement in the small Raman frequency shift medium; a simple and effective design and experimental verification of SRS suppression method.Firstly, starting from the classical electromagnetic theory of SBS and SRS respectively, analyzes the SBS and SRS in the interaction process with materials, obtained the SBS steady state and transient conditions of vibration equation, the pump and Stokes coupling equation of SRS, the steady state and transient gain of SRS.Secondly, according to the theoretical result, establish the scheme of the relationship between SBS and SRS from SRS gain coefficient: use broadband laser(532 nm Nd:YAG mode-locked laser) as a pump source, the filtered forward SRS interact with pump light(coaxial direction and pulse waveform peak overlap) to amplify the first-order Stokes, finally using the spectral method to separate the first-order Stokes, measuring the first-order Stokes energy before and after amplification, the pump energy, pump and Stokes’ space-time overlapping effective area and pulse width, by simplified calculation the SRS gain coefficient of the medium is obtained. And on the basis of the results of the experiment of heavy fluorinated carbon materials, analyze the advantages and disadvantages of them as a SBS medium.Finally, through theoretical analysis, design a simple solution that can suppress the SRS, particularly insert a beamspliter in the interaction medium to separate the Stokes. Using this method under the pump of 700 MW/cm2, the forward SRS effect reduced 2.88 times, this method is simple in structure, can be repeatedly used in the media application many times in order to further reduce the phenomenon of the SRS.更多还原