【作者】 李锋；

【导师】 侯洵；

【作者基本信息】 西北大学 ， 光学， 2007， 博士

【摘要】 激光二极管泵浦全固态蓝光激光器具有效率高、稳定性好、结构紧凑、小型化、寿命长等优点，在医学、激光演示、同位素分离、超高密度光存储、精密材料加工、海洋资源探测、光谱分析等领域具有广泛的应用，是近年来全固体激光器件的研究热点。本文主要工作是对激光二极管泵浦、腔内倍频蓝光激光器进行了系统、全面的研究，并取得以下几方面的成果：1、回顾了全固态激光器的发展历程、特点及其应用，蓝光激光器的研究背景以及实现蓝色激光输出的方法。综述了国内外激光二极管泵浦全固态蓝光激光器的研究进展。2、从准三能级速率方程理论出发，考虑介质再吸收损耗几种泵浦方式下的激光阈值、斜效率，讨论了端面泵浦下激光晶体最佳晶体长度。结果表明，端面泵浦时，在泵浦功率不是很大的情况下，应使晶体的长度接近于最佳值，以使阈值最低。当泵浦功率相当大时，增加晶体长度对外部斜效率的提高贡献大。侧面泵浦时，高斯光束泵浦更有利于系统低阈值运转，大礼帽泵浦光分布有利于大功率激光输出。比较了几种常用于蓝光的激光晶体的物理、光学特性。3、讨论了绝热极限下准单色三波耦合过程，分别给出了小信号和大信号下的二次谐波转换效率。讨论了非线性光学相位匹配效率问题，对几种可实现蓝光输出的非线性光学晶体的特性进行了分析与比较。4、采用传播圆图解方法分析了几种常用于固体激光器的光学谐振腔的动态工作特性。V型和Z型谐振腔中，影响其稳区宽度及激光晶体中光模半径的主要因素是其第一臂的长度，宽的热稳区和大的光模半径往往不可兼得。讨论了V型折叠腔的像散，在腔内插入布儒斯特片能在一定的热动力范围内近似补偿折叠腔的像差。5、采用数值方法研究了复合激光介质的温度场及热透镜效应，并与相同条件下的普通晶体比较。结果表明，吸收系数越大，两种晶体中最高温度相差也越大。相同条件下复合晶体与普通晶体的f_GRIN值接近，但其热透镜效应明显低于普通晶体。热效应下的相位延迟与球面透镜相比存在高阶球差，在激光系统工作中应选择最佳模半径比（W_o／W_p）从而兼顾斜效率和光束质量。用实验方法探测了激光晶体中热效应产生的干涉图样。6、采用光腔衰荡法测量了在所需波长同批次激光镜片的反射率。采用3W半导体激光二极管（LD），经过耦合系统泵浦Nd：YAG晶体，采用Ⅰ类相位匹配BIBO晶体腔内倍频，获得了220rmW 473nm蓝光，光转换效率达到7.3％，系统输出功率稳定性优于3％。对研究结果进行了产品化开发，产品体积小，能耗低，效率高，输出光斑好，性能稳定可靠。采用光纤耦合大功率半导体激光端面泵浦Nd：YAG晶体，折叠腔结构最大获得了3.2W、946nm的红外光。在腔内引入BIBO倍频晶体，最大输出了710mW的473nm的蓝光，此系统正在进一步优化和产品工程技术转化之中。在腔内测量了LD端面泵浦Nd：GdVO₄晶体900nm附近的激光谱线，发现四能级跃迁直接影响准三能级激光的有效运转，而其900nm附近的则跃迁由于腔损耗的增大而蓝移。更多还原

【Abstract】 Laser diode（LD） pumped all solid state blue lasers have more advantages than traditional gas blue lasers, such as high efficiency, compactness, high stability, and long lifetime. They are widely used in many fields such as medicinal diagnose, precise machining, spectroscopic analysis, optical printing, high density data storage, isotope separation, scientific research and laser entertainment in general, and it is a hotspot of all-solid-state laser research in recent years. In this dissertation, the theoretical and experimental research on LD pumped all solid state blue laser can be outlined as:1. The development process of all-solid-state lasers was presented firstly, as well as its main characters and application field. The researching background of LD pumped all-solid-state blue lasers were introduced along with methods to achieve blue laser, and research evolution of blue laser were summarized over domestically and abroad.2. According to theory of qausi-three-level lasers, considering re-absorption lose of laser medium, laser threshold and slope efficiency was investigated for several circumstances, as well as optimal crystal length. The results show that an optimal laser crystal length can lead a minimum threshold for the system at low pump power, and larger crystal means higher external slope efficiency at higher pump power. Gaussian pump energy makes for low threshold for side pump configuration, while top-hat pump energy is propitious to high out put power. Physical and optical properties of several laser crystals used in blue lasers were compared.3. Considering the process of quasi-homochromatic three light wave coupling under adiabatic utmost, second harmonic conversion efficiency were present under little and large signal approximation. Non-linear optical phase matching efficiency was discussed here. Property of several nonlinear optical crystals of blue lasers were compared.4. A graphic analyze method were used to analyze the working property of V and Z type folded laser resonator under the effect of thermal lens of laser medium. The stable range of these resonators was influenced mainly by the length of its first arm, a wider thermal stable range means smaller optical module. The V type folded resonator’s astigmatic can be compensated partly by insert a suitable Brewster plate in the cavity.5. Temperature field and thermal lens effects of laser diode end pumped composite YAG rod were investigated and compared with conventional Nd:YAG through a numerical analysis method. The results shown that the highest temperature of these laser medium discrepant increasing as absorption coefficient increase under the same pumping condition, and the value of f（GRIN） close to each other approximately, this means little thermal length effect in composite laser rod. Phase detention of thermal effect cannot be equivalent to a spherical lens, and thus an optimization module ratio （W_o/w_p） of pump and laser mode should be choice in a laser system. Interference pattern of thermal effect of laser crystal were detect experimentally.6. Experimental research: Firstly, reflectivity of laser cavity mirror was measured by Cavity-Ring-Down method. Following that, we utilizing 3W LD laser end pumped Nd:YAG crystal, and type I phase matching BIBO nonlinear crystal were select for intra-cavity frequency doubling blue laser, 220mW blue laser at 473nm were obtained, corresponds to an optical-optical conversion efficiency of 7.3%. And the stability of blue laser excelled 3%. A new type of high efficiency blue laser product with good beam quality and high stability was exploited based on our research results.Secondly, in another experiment, fiber coupled high power diode laser were select to end pump Nd:YAG crystal, 3.2W infrared laser at 946nm were obtained. BIBO were selected for intra-cavity frequency doubling, 710mW blue laser at 473nm were obtained. This laser system is in process of optimizing and production engineering realize.Laser spectrum around 900nm of Nd:GdVO₄ crystal were measured in cavity. The result shown that quasi-three level laser were depleting directly by four level lasers transition. Transitions around 900nm of Nd:GdVO₄ show a blue shift at increasing cavity losses.更多还原