全固态拉曼激光器理论与实验研究

【作者】 丁双红；

【导师】 张行愚；

【作者基本信息】 山东大学 ， 光学工程， 2006， 博士

【摘要】 目前，受激拉曼散射（SRS）是重要的变频技术之一。受激拉曼散射光的光谱可遍及紫外到近红外，大大拓宽了激光光谱范围。此外受激拉曼散射具有多种优良特性，如散射光光束质量好、脉宽窄、不需要相位匹配、并且具有高的转换效率。近年来，多种人工生长的晶体被发现是优良的拉曼介质，例如Ba（NO₃）₂、BaWO₄、KGd（WO₄）₂和YVO₄晶体等。与传统的气体和液体拉曼介质相比，固体拉曼介质具有粒子浓度大、体积小、拉曼增益系数大及热导性能好等优点。以晶体作为拉曼介质的固体拉曼激光器结构紧凑、效率高、稳定性好，在信息、交通、测量、医疗、国防和工农业等领域都有重要的应用。 现今固体拉曼激光器是非线性光学和固体激光器领域的研究热点。俄罗斯科学家在晶体拉曼介质生长和固体拉曼激光器研究方面做了许多开创性的工作，居世界领先地位。此外美国、德国、澳大利亚和中国台湾等国家和地区的研究者都在积极地参与固体拉曼激光器的研究。我国在晶体生长领域居国际先进水平，近几年生产的一些晶体，如SrWO₄、PbWO₄、BaWO₄、Nd：KGd（WO₄）₂等都是优良的拉曼介质，但在中国大陆固体拉曼激光器的研究相对滞后，至今没有关于全固态拉曼激光器的研究报道。 气体介质中的受激拉曼散射的理论研究较为充分。晶体中的受激拉曼散射由于发展较晚，其理论研究及固体拉曼激光器的理论研究尚不成熟。与气体介质相比，晶体介质具有各向异性、拉曼增益系数大、双折射和光学声子寿命短等特点。晶体中的受激拉曼散射理论，及以此为基础的固体拉曼激光器理论是高性能固体拉曼激光器的研制基础。 本论文以KGd（WO₄）₂、SrWO₄和Nd：YVO₄晶体作为拉曼介质，对外腔式、内腔式及自拉曼激光器进行了系统的理论和实验研究。本文研究的具体内容为： 1．在波动方程和受激拉曼散射物质方程的基础上，考虑高至三阶斯托克斯光及后向受激拉曼散射，在稳态近似下，建立了外腔式固体拉曼激光器新的辐射传输理论模型。同时对辐射传输方程进行了归一化处理，给出了数值算法。辐射传输方程被实验结果证明可以准确地描述外腔式固体拉曼激光器内基频光与散射光之间的相互作用，可以辅助设计外腔式固体拉曼激光器，以实现某阶斯托克斯光的最大转换效率。 2．作为辐射传输方程的近似理论，首次推导了外腔式拉曼激光器的速率方程理论模型。在速率方程中考虑了高至三阶斯托克斯光，并对速率方程进行了归一化处理。通过比较两种理论模型的数值结果，证明了速率方程理论在低拉曼增益（归一化拉曼增益系数G_L＜4）、长泵浦脉宽（归一化泵浦脉宽N_L＞50）情况下，与辐射传输方程有较好的近似。 3．分别数值求解了归一化辐射传输方程和速率方程，对一阶斯托克斯光输出进行了数更多还原

【Abstract】 Stimulated Raman scattering （SRS） can shift the laser frequency over a fixed frequency gap to produce new laser lines. The laser spectrum reachable with SRS extends from ultraviolet to near infrared. SRS possesses many attractive features, i.e. beam clean-up, pulse compression, no need for phase matching, and high conversion efficiency. A good number of crystals have been found to be Raman-active, such as Ba（NO₃）₂, BaWO₄, KGd（WO₄）₂ and YVO₄ crystals. As compared with the traditional gas and liquid Raman media, the Raman crystals offer high gain, high molecule density, good thermal and mechanical properties. Presently, the SRS in crystal media is one of the most important mechanisms to generate new laser lines, and can realize the compact, all-solid-state Raman lasers, which have important applications in various fields.At present, all-solid-state Raman lasers attract intensive research interest in the field of solid-state laser and nonlinear optics. Scientists from Russia act as the leading role in the regime of Raman crystal growth and research on the solid-state Raman lasers. Researchers from America, Germany, Australia and other countries are taking part actively in the field of the all-solid-state Raman lasers. China is renowned for the advanced crystal growth technology, and recently, some Chinese institutes and companies offer the Raman media of the good quality, e.g. SrWO₄, PbWO₄, BaWO₄, and Nd:KGd（WO₄）₂ crystals. However, the research on the solid-state Raman laser lags behind, and up to now, there has been no work on the solid-state Raman lasers reported in the Chinese Mainland.Owing to the lack of practical Raman crystals in the early years, the intensive study of the SRS in crystals just began in 1980s. There are plenty theoretical works done on the SRS processes in the gas media, and relatively little effort exerted on the theoretical work of the SRS in the crystals. The crystalline media possesses much different features to the gas counterparts, and the theoretical research on the SRS in the crystals and theories of the all-solid-state Raman lasers are the bases of the development of all-solid-state Raman lasers of high performance.This dissertation presents a full and systematic theoretical and experimental study on the characteristics of the extracavity, intracavity, and self-Raman lasers with KGd（WO₄）2, SrWO₄ and Nd:YVO₄ crystals as the Raman media. The main content of this dissertation is as follows1. Based on the wave equation and SRS material equations, and with up to the third Stokes and backward Raman scattering to be considered, a new set of radiation transfer equations was deduced for the solid-state extracavity Raman lasers in the steady-state regime. The radiation transfer equations were normalized, and the numerical method was given. The numerical results of the radiation transfer equations were in good agreement with the experimental ones.2. As an approximate and simplified theoretical model, the rate equations of the extracavity更多还原