激光二极管端面泵浦微片激光器热效应的研究

发布时间：2018-02-24 06:07

本文关键词： 激光器 Yb:YAG晶体热导率热效应　出处：《西安建筑科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：20世纪60年代,从此半导体泵浦的固体激光器诞生了[1]。早在1962年世界上第一支激光二极管问世后不久,美国MIT实验室的Keyes等人就用它来作为固体激光的泵浦源,并且用实验的方法获得输出了准连续激光束[1]。与传统的固体激光器相比,激光二极管泵浦的全固态激光器(DPSSL)有着自己独特的特点,主要的表现是光光转换效率很高,体积比较小,性能非常可靠、寿命长,光束质量好等,被广泛的应用于各个领域[2]。伴随着全固态激光器应用领域的不断发展,人们对激光的输出功率和光束质量的要求越来越高。伴随着激光器输出功率的大幅度提高,在激光晶体内会产生严重的热效应问题,热效应会使激光系统的效率降低,光束质量变差,甚至损坏激光晶体,特别是对于端面泵浦的固体激光器中,泵浦光通常被聚集在一个很小的光斑,从而光斑范围内的热功率密度非常大,因此对于热效应的研究非常重要。本文是在激光二极管泵浦的全固态激光器的理论基础上对Yb:YAG微片激光器的热效应进行研究,在以往的研究中,人们往往将Yb:YAG激光晶体的热导率视为常数,而在本论文中作者通过对相关资料和文献的查阅发现,Yb:YAG晶体的热导率是随着温度的变化而发生变化的,其热膨胀系数也是随着温度变化的,这样一来,其研究结果将更加的符合实际情况,本文将通过这两个创新点对Yb:YAG微片晶体的热效应展开研究,主要内容为:1.回顾了激光二极管泵浦的全固态激光器的发展历史,介绍了全固态激光器的国内外研究现状和发展方向以及研究热点,介绍了激光二极管的泵浦方式,提出了减小热效应的方法,并详细阐述了Yb:YAG晶体的特点和工作特性。2.对激光二极管端面泵浦圆形和方形Yb:YAG微片激光器的热效应展开研究,在研究中考虑到Yb:YAG晶体的热导率随着温度变化的量,建立热模型,构造初始和边界条件,应用数理方程的知识对Yb:YAG晶体的温度场就行计算,得到温度场的一般解析表达式。利用Mathematic软件进行模拟,分析泵浦功率,光斑半径,超高斯阶次,微片尺寸等因素对Yb:YAG微片激光器热效应的影响分布图。3.对脉冲激光二极管端面泵浦方形Yb:YAG微片激光器的热效应展开研究,通过解热传导方程得到温度解析表达式,定量分析了单脉冲泵浦过程中超高斯阶次,泵浦功率,光斑半径,脉宽等因素对Yb:YAG晶体瞬时温度场的影响以及在非稳态周期脉冲过程中与准热平衡态时温度场的变化规律。将此方法应用到其他激光器热效应的研究中,为有效解决二极管泵浦过程中的热效应问题提供了理论依据。
[Abstract]:In 1960s, the semiconductor pumped solid-state laser was born [1]. As early as 1962, shortly after the first laser diode came out, Keyes et al., from the MIT Laboratory of the United States, used it as the pump source of the solid-state laser. Compared with the conventional solid-state laser, the all-solid-state laser (DPSSL) pumped by laser diode has its own unique characteristics, and the main performance is that the optical conversion efficiency is very high. Small size, reliable performance, long lifetime, good beam quality and so on, have been widely used in various fields [2]. With the development of all solid-state laser applications, With the great improvement of laser output power, there will be serious thermal effect in laser crystal, and the thermal effect will degrade the efficiency of laser system. The beam quality becomes worse, and even destroys the laser crystal, especially in the end pumped solid-state laser, the pump light is usually gathered in a very small spot, so the thermal power density in the spot range is very large. Therefore, the study of thermal effect is very important. In this paper, the thermal effect of Yb:YAG microchip laser is studied based on the theory of all-solid-state laser pumped by laser diode. The thermal conductivity of Yb:YAG laser crystal is often regarded as a constant. In this paper, the author finds that the thermal conductivity of Yb: YAG crystal changes with the change of temperature. The coefficient of thermal expansion also changes with the temperature, so the results of the study will be more in line with the actual situation. In this paper, the thermal effects of Yb:YAG microcrystals will be studied through these two innovative points. The development history of all-solid-state laser pumped by laser diode is reviewed, the research status, development direction and research hotspot of all-solid-state laser at home and abroad are introduced, and the pumping mode of laser diode is introduced. The method of reducing thermal effect is proposed, and the characteristics and working characteristics of Yb:YAG crystal are described in detail. 2. The thermal effect of round and square Yb:YAG microchip laser pumped by laser diode is studied. Taking into account the variation of thermal conductivity with temperature of Yb:YAG crystal, the thermal model is established, the initial and boundary conditions are constructed, and the temperature field of Yb:YAG crystal is calculated by using the knowledge of mathematical equation. The general analytical expression of temperature field is obtained. The pump power, spot radius, order of exceeding Gao Si are analyzed by Mathematic software. Effect of microchip size on thermal effect of Yb:YAG microchip laser. 3. The thermal effect of a pulsed laser diode end-pumped square Yb:YAG microchip laser is studied, and the analytical expression of temperature is obtained by using the heat conduction equation. The order of super Gao Si, pump power and spot radius during monopulse pumping are quantitatively analyzed. The influence of pulse width and other factors on the instantaneous temperature field of Yb:YAG crystal and the variation of temperature field in the unsteady periodic pulse process and the quasi-thermal equilibrium state are studied. The method is applied to the study of the thermal effect of other lasers. It provides a theoretical basis for solving the thermal effect in diode pumping process.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN248

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