【作者】 张玉；

【导师】 李健；

【作者基本信息】 山东师范大学 ， 光学， 2010， 硕士

【摘要】 LD泵浦的全固态激光器（Laser diode pumped solid-state laser）具有效率高、寿命长、工作稳定、结构紧凑、可全固化等优点,是近年来国际上发展最快、最有潜力的激光器之一。在国防、军事、科研、光通讯、材料加工、医疗卫生、光电子产业等领域获得了广泛应用。但是,激光的工作物质吸收泵浦能量后会在激光晶体内产生不均匀的温度梯度,引起端面形变,并和热效应引起的激光晶体折射率的变化共同作用,产生热透镜效应,严重影响了激光光束的质量和激光效率的提高,给激光器的设计和应用带来了相当大的阻碍。所以,抑制和消除激光晶体的热效应就成为全固态激光器研究中的关键因素之一。本文以Yb:YAG晶体为例,通过建立激光晶体热传导模型,求解泊松方程,得到不同Yb³⁺离子掺杂浓度的Yb:YAG晶体内温度场分布及由此引起的光程差和热焦距,并求出在不同泵浦半径下的端面温度分布。研究结果表明:随着Yb³⁺离子掺杂浓度增加,Yb:YAG晶体端面中心温度升高,晶体中心轴温度衰减加快,热焦距则越小。而随着泵浦光斑半径的增大,晶体端面中心温度降低。由于激光晶体类型广泛,热效应的计算过程比较繁琐,计算热效应的程序和方法非常的混杂,一直以来都没有统一的要求或者规则。在计算、科研过程中难免会给使用者造成不必要的困扰,浪费大量宝贵的时间和精力,大大的降低了科研的效率。而且以往的计算都没有考虑晶体周边与冷却液之间的对流传热,这就大大影响了计算的精确度,对于激光器的稳定性非常的不利。在此,我们将更全面考虑影响晶体热效应的因素,并利用计算机混编语言建立一个以界面的形式测算激光晶体热效应的软件系统,为激光晶体的使用和科研提供一个更便捷方法。其主要内容如下:1.对全固体激光器的发展历史进行了回顾;分析了全固态激光器的主要特性;介绍了激光晶体热效应的产生原因及不良影响。2.根据激光晶体热效应的基本理论,建立了热效应的理论模型;介绍了几种常用的计算方法;找到了抑制和消除激光晶体热效应的不同因素。3.建立了矩形截面Yb:YAG晶体的热模型,通过求解热传导Possion方程,得到了不同Yb³⁺离子掺杂浓度的Yb:YAG晶体内温度场分布以及由此引起的光程差和热焦距,并求出在不同泵浦半径下的端面温度分布。当泵浦功率为10W、泵浦光斑半径为320μm,Yb³⁺掺杂浓度分别为5at.%、10at.%、20at%时,Yb:YAG晶体端面最高温度分别为67.7℃、147.8℃、247.7℃,即Yb³⁺掺杂浓度越高,晶体端面中心温度越高,热透镜效应越严重;对于同一个Yb:YAG晶体,当泵浦半径分别为200μm、320μm、400μm,其端面中心温度分别为174.6℃、147.8℃、134.9℃。即泵浦光半径越小,其端面中心温度越高,这一结论对于改善Yb:YAG晶体热效应提供了理论依据。4.利用计算机混编语言,将完成的计算热效应的matlab程序联系起来,形成一个整体软件,以界面输入参数的形式,快速方便的完成对不同晶体热效应的计算和输出。更多还原

【Abstract】 Diode-pumped solid-state laser is widely used in national defence, military, basic research, communication, material processing, medical therapeutics and sanitation, photoelectron industry etc. It has lots of advantages, such as high efficiency, long lifetime, stability, compactness and all solid-state construction. So, it has become the researching emphasis because unique merits. In the design of laser diode end-pumped all-solid state lasers,a temperature gradient is formed in the laser crystal and as a result of the absorption of the pump power, the temperature at the center of the laser crystal is higher than the edge, so a deformation of the surface appeared and a thin convex was formed. Moreover, the change of refractive index of the laser crystal devotes to the thermal lens effect and makes the designing of the laser cavity more difficult. The matter of hindering scaling of diode-pumped solid-state lasers is heat deposition within the laser medium. The thermal conduct model of laser crystal was established.Using Possion equation, the temperature distributionin, the OPD and focal length in Yb:YAG crystal were obstained with different Yb ions concentration. Based on the former calculation, we obtained the temperature distribution of end-face with different pumping radius. The study shows that in the same condition, when the Yb ions concentration increase, the central temperature of Yb:YAG crystal’s pumped face will rise and the temperature of crystal central axis will reduce-faster,and the focal length will lower.When the pumping radius increase,the central temperature of Yb:YAG crystal will reduce.As the laser crystal type of broad, the calculation of thermal effect of the process is relatively complicated to calculate thermal effects of the procedures and methods is very mixed, that has been no uniform requirements or rules.In the calculation, users of the research process will inevitably cause unnecessary distress, wasting valuable time and energy, greatly reduces the efficiency of scientific research. And the calculation did not take into account the past and cooling liquid crystal between the subordinate of the convective heat, which greatly affect the accuracy of the calculation for the stability of the laser is very negative. Here, we will be more fully into account the factors that affect the crystal thermal effects, and use the computer to build a mixed language interface in the form of specialized measurement systems thermal effect of laser crystals, laser crystals for the use and scientific research to provide a more comprehensive measurement system.The contents can be outlined as follows:1. Reviewed the history and progress of diode-pumped solid-state lasers; and analysed the characters of the diode-end-pumped solid-state laser; then presented the cause of engendering and the harmful effect of laser crystal.2. On the basis of the thermal effect theory of laser crystal. By using this theory, the thermal conduct model of laser crystal was established. Some considerations of useful methods were presented. And then found the difference elements of elimination and inhibition.3. The rectangle thermal conduct model of Yb:YAG laser crystal was established. Using Possion equation,the temperature distribution, the OPD and the thermal focal length in Yb:YAG laser crystal were obstained with different Yd ions concentration, and the temperature of pumped face distribution was obtained with different pumping radius. When the pumping power is 10W, the radius of pumping beam is 320μm, and the Yd ions concentration separately were 5at%, 10at%, 20at%, the central temperature of Yb:YAG crystral is 67.7℃,147.8℃,247.7℃. we obtained that , when the Yb ions concentration increase, the end-pumped central temperature of Yb:YAG crystal’s was higher, the thermal effect was aggravating. When the radius of pumping beam are 200μm, 320μm, 400μm, the central temperature of end-pump is 174.6℃,147.8℃and 134.9℃. When the pumping radius reduce, the central temperature of Yb:YAG crystal will higher. The conclusion will give a theoretical direction for improving the thermal effect of Yb:YAG crystal.4. Using the computer being enrolled together language, the computation thermal reaction matlab procedure association which will complete is, forms an over all software, by contact surface input parameter form, fast convenient completion to different crystal thermal reaction computation and output.更多还原