【作者】 刘善德；

【导师】 何京良；

【作者基本信息】 山东大学 ， 凝聚态物理， 2014， 博士

【摘要】 受激拉曼散射属于光学三阶非线性范畴,是实现激光频率变换的有效途径之一。拉曼散射光的光谱范围可以覆盖紫外到近红外波段,因而在信息科学、激光测量、激光医疗及国防等领域都有重要的应用价值。而基于晶体拉曼增益介质的全固体拉曼激光器,因晶体材料粒子浓度大、体积小、拉曼增益系数高、热学和机械加工性能优良而备受关注,已成为拉曼激光器的研究热点。目前来讲,比较常用的拉曼晶体材料主要有BaWO4、KGW、Nd:YVO4、Nd:GdVO4等晶体,但因每一种晶体都有其使用的局限性,且输出波长依赖于晶体的晶格振动模式。因而,人们去追逐和探索一些新型实用拉曼晶体材料的脚步从未停歇,这些晶体材料具有丰富的拉曼振动模式、大的拉曼增益系数、良好的热学及机械加工性能、高的激光损伤阂值、以及优良的晶体生长习性。α-BaTeMo2O9(α-BTM)晶体就是新型拉曼晶体材料的优秀代表。本论文对新型α-BTM晶体拉曼激光器进行了全面的分析和实验研究。α-BTM晶体是由山东大学晶体材料国家重点实验室生长,具有大的晶体尺寸、宽的通光波段、丰富的拉曼振动模式,适中的稳态拉曼增益系数和热导率,较高的激光损伤阈值。首先,基于晶体的结构,论文从理论上对其所有的振动模式进行分类,并计算了不同拉曼几何配置下的拉曼散射效率,找到了拉曼振动峰与原子振动基团的对应关系；通过自发拉曼光谱比较法,计算了α-BTM晶体Z(XX)Z拉曼配置下的稳态拉曼增益系数；在理论分析的基础上,实验上全面的研究了在不同泵浦条件下,α-BTM晶体的受激拉曼散射输出特性,分别实现了一阶、二阶和三阶斯托克斯拉曼激光的高效输出及其二阶和三阶拉曼激光的同时输出,研究结果表面,α-BTM晶体是一种优良的拉曼增益材料,具有实用化的潜力,具体论文研究内容如下：1、对α-BTM晶体的晶体结构、基本的热学和光学性质进行简单介绍,根据其晶体结构特点,理论上对其312个晶格振动模式进行分类：Г=78A1+78A2+78B1+78B2,且这些振动模式都具有拉曼活性,计算了α-BTM晶体的拉曼散射效率,分别给出了四种晶格振动模式所对应的偏振拉曼光谱几何配置；实验上分别测试了X、Y及Z方向通光的自发偏振拉曼光谱,实验结果与理论计算数据吻合；给出了原子振动基团与拉曼频移峰之间的关系,最强拉曼散射频移峰-900cm1是Mo-O-Mo的反对称振动产生。(第二章)2、详细地介绍了几种常用的自发拉曼增益系数计算方法,用自发拉曼光谱比较法计算了α-BTM晶体Z(XX)Z拉曼配置下的稳态拉曼增益系数,其大小约为2.4cm/GW@1.06μm;建立了内腔、外腔拉曼激光器速率方程,从理论上可以对实验进行指导；首次实现了a-BTM晶体的一阶斯托克斯拉曼激光器输出：采用闪光灯泵浦Nd:YAG激光器外腔泵浦方式,实现了15.1mJ,1.178μm—阶斯托克斯拉曼激光输出,光光转换效率为31.5%；采用脉冲LD泵浦Nd:YAG/Cr4+:YAG内腔泵浦方式,实现了1.07mJ,1.178μm拉曼激光输出,重复频率670Hz,从LD到一阶斯托克斯激光的光光转换效率和斜效率分别是10%和13.8%,对激光的脉冲形状进行了定性分析,这种百赫兹重频的短脉冲激光器在激光测距方面有其潜在的应用价值；将α-BTM晶体置于Nd:YLF模块声光调Q激光谐振腔中,实现了2.7W,1.1641μm拉曼激光输出,获得的最高单脉冲能量和峰值功率分别是1.08mJ和67.5kW。(第三章)3、在一阶斯托克斯拉曼激光的实验研究基础上,对谐振腔进行优化设计,采用Nd:YLF模块内腔泵浦方式,实现了α-BTM晶体二阶斯托克斯拉曼激光输出,最大输出功率、单脉冲能量和峰值功率分别为1.37W、0.55mJ和137kW；采用大能量灯泵Nd:YAG激光器泵浦,实现了二阶和三阶双波长拉曼激光同时输出,最大总输出能量为27.3mJ,包含20.1mJ的1.32μm二阶斯托克斯激光和7.2mJ的1.5μmm三阶斯托克斯激光,光光转换效率为35.9%,斜效率为54.5%,并对不同输出耦合条件下,二阶、三阶斯托克斯激光的能量输出关系进行了分析。(第四章)4、理论分析了激光晶体和拉曼增益介质的热效应问题,分别给出了两者的热焦距表达式；为获得更高能量的1.5μm人眼安全波段激光输出,对谐振腔进行了优化设计,采用灯泵的Nd:YAG激光器作为泵浦,实现了16.5mJ的拉曼激光输出,其中1.5μm的输出能量为14.5mJ,1731nm四阶斯托克斯波长输出能量为2mJ,整体光光转换效率和斜效率为21.7%和32.6%。最高泵浦能量下,三阶和四阶拉曼激光的脉冲宽度分别是8.6ns和5.2ns。(第五章)论文的主要创新工作包括：1、理论上系统的研究了α-BTM晶体拉曼光谱特性,包括：拉曼振动形式的分类、拉曼散射效率的计算以及拉曼振动峰与原子振动基团的关系。2、测试了不同拉曼几何配置下的自发偏振拉曼光谱,计算了α-BTM晶体Z(XX)Z配置下的拉曼增益大小约为2.4cm/GW@1.06μm。3、首次实现了α-BTM晶体一阶斯托克斯拉曼激光输出,在不同的激光泵蒲条件下,实现了最高输出能量为15.1mJ,最大输出功率2.7W,输出波长在1.17μm。4、研究了α-BTM晶体二阶和三阶斯托克斯同时输出特性。实现了20.1mJ的1.32μm和7.2mJ的1.5μm拉曼激光同时输出。5、通过谐振腔的优化设计,获得了14.5mJ,1.5μm人眼安全波段激光输出和2mJ,1.73μm四阶斯托克斯激光输出,光光效率和斜效率达到21.7%和32.6%。更多还原

【Abstract】 Stimulated Raman scattering is one of the important frequency conversion methods, belonging to the third-order nonlinear optics. The scattering spectra range from UV to Near-infrared, which have the potential applications in information science, laser measurement, laser medicine and national defense. Due to the small size, high Raman gain coefficient and good thermal and mechanical properties of the crystal materials, all solid-state Raman laser has become one of the most avtive fields in the Raman laser research. Among the Raman crystal materials, BaWO4, KGW, Nd:YVO4, and Nd:GdVO4et al are most used to generate Raman laser. However, each kind of Raman crystals are with certain limitation in Raman application and the scattering wavelength is dependent on the lattice vibration mode. The steps for exploring novel and practical Raman crystal material are never stop. These Raman crystals have the advantage porperties in terms of abundant Raman vibration mode, high Raman gain coefficient, good thermal an mechanical properties, high laser damage threshold, and good crystal grow habit.This paper have theoretically and experimentally studied the performace of the stimulated Raman scattering lasers based on a novel Raman material, α-BaTeMo2O9crystal. The α-BaTeMoaO9crystal was grown by the State key lab. Of crystal materials, Shandong University, which possesses lager size, wide transmission bands, abundant Raman vibration mode, moderate Raman gain coefficient and thermal conductivity, and high laser damage threshold. Firstly, we have classified the all lattice vibrational mode and calculate the Raman scattering coefficiency with the different Raman configurations. The relationships between Raman vibration peak and atom vibration group were given. In addition, by using the method of spontaneous Raman spectra comparision, the steady-state Raman gain coefficient of a-BaTeMo2O9crystal with Z(XX)Z Raman configuration was calculated. Based on the analysis of the Raman spectra, the generations of the α-BaTeMo2O9Raman laser have been systematic investigated. The high efficiency first-order, second-order, and third-order Stokes Raman laser have been obtained based on the α-BaTeMo2O9crystal, respectively. What is more, a second-order and third-order simulataneous dual-wavelength Raman laser generation was also achieved. The main content of this dissertation includes:1. The structure of lattice and optical and thermal properties for α-BaTeMo2O9crystal have been simply introduced. Based on the crystal structure, all of the vibration mode was calculated and classified as follows:Г=78A1+78A2+78B1+78B2, and group theory predicts that all of the vibration mode belong to Raman activel mode. The Raman scattering coefficient was calculated and the relationships between Raman vibration peak and atom vibration group were given, in which the～900cm-1Raman shifing was generated by antisymmetric stretching modes of the Mo-O-Mo bridge. The X-, Y-and Z-cut polarized spontaneous Raman spectra were measuremented, and the experimental results were consistent with the theoretical analysis.(Chapter2)2. The methods for the calculation of Raman gain coefficient were systemically introducted. The Raman gain coefficient of the α-BaTeMo2O9crystal with Z(XX)Z configuration was calculated to be2.4cm/GW@1.06μm by the method of spontaneous Raman spectra comparision. The rate equations have been established to guide the experiments for intracavity and extracavity Raman lasers. The first-order Stokes Raman laser based on the bulk α-BaTeMo2O9crystal was firstly studied:By using a lamp-pumped Q-switched Nd:YAG laser as a Raman pump source, a maximum1.178μm first-order Stokes pulse energy of15.1mJ was achieved with a optical-to-optical conversion efficiency of31.5%; A maximum pulse energy of1.07mJ Raman laser was obtained driven by a pulsed laser diode pumped Nd:YAG/Cr4+:YAG laser with repetition rate of670Hz. This kind of lasers have a potential application in laser ranging. With a diode-side-pumped Nd:YLF Q-switched laser intracavity pumping, a maximum1.164μm Raman output power was2.7W, corresponding to the maximum single pulse energy and peak power of1.08mJ and67.5kW, respectively.(Chapter3)3. Based on experimental research on the first-order Stokes Raman laser, a second-order Raman laser was achieved with optimum resonator design, driven by a diode-side-pumped Nd:YLF laser. The maximum output power, single pulse energy and peak power were1.37W,0.55mJ and137kW, respectively. We firstly demonstrated a dual-wavelength α-BaTeMo2O9Raman laser with the second and third-order Stokes wavelength simultaneous output. A total maximum output pulse energy of13.6mJ was achieved, giving a optical-to-optical conversion efficiency and a slope efficiency of35.9%and54.5%, respectively, which contains20.1mJ second-order Stokes pulse energy and7.2mJ third-order Stokes pulse energy. What is more, the relationship between second-order and third-order Stokes output energy and output coupler was analysed in details.(Chapter4)4. The thermal effect for laser crystal and Raman gain medium have been systematic studied, and the thermal focusing length were given through theoretical derivation. With optimum optical resonator design, a high pulse energy eye-safe Raman laser was achieved, with1.5μm output pulse energy of14.5mJ and1731nm four-order Stokes pulse energy of2mJ, corresponding to a optical-to-optical conversion efficiency of21.7%and a slope efficiency of32.6%, respectively. At the maximum pump pulse energy, the pulse widths for the third-and four-order Stokes pluse were8.6ns and5.2ns, respectively.(Chapter5)The main innovations:1. The characteristics of the α-BaTeMo2O9Raman spectra were systemically studied: the classfication of the lattice vibration mode; the calculation of the Raman scattering coefficiency; relationships between Raman vibration peak and atom vibration group.2. The polarized Raman spectra have been measuremented with different Raman configuration and the steady-state Raman gain coefficient was calculated to be2.4cm/GW@1.06μm.3. We firstly demonstrated a first-order Stokes Raman laser based on a novel α-BaTeMo2O9crystal. The maximum first-order Stokes laser single pulse energy of15.1mJ and output power of2.7W were ontained, respectively, with different pump conditions.4. The performance of second-and third-order Stokes dual-wavelength Raman laser was investigated, with the second-order Stokes output pulse energy of20.1mJ and the third-order Stokes pulse energy of7.2mJ.5. With optimum resonator design, a maximum pulse energy of14.5mJ at1.5μm and2mJ at four-order Stokes wavelength1731nm laser was achieved, with a optical-to-optical conversion efficiency and a slope efficiency of21.7%and32.6%, respectively.更多还原