全固态高功率Nd：YAG激光器及其二次与四次谐波产生的研究

【作者】 李修；

【导师】 白晋涛；

【作者基本信息】 西北大学 ， 光学， 2009， 博士

【摘要】 与传统的激光器相比,激光二极管(LD)泵浦的全固态激光器具有重量轻、效率高、结构紧凑、光束质量高、使用寿命长、维护费用低廉等一系列优点使其逐步替代气体、染料等激光器而在军事、工业、医疗、科研以及通讯等领域有着广泛的应用。利用非线性频率变换技术,使近红外的光波变频后产生的激光拓展了激光器在实际中的应用领域。如532nm的激光在激光医学、激光显示方面有着广阔的应用前景;而波长更短的266nm紫外激光器在精密材料加工、光刻、光印刷等领域则有着独特的优势。本论文的主要工作如下:1.从理论上分析了多向侧面泵浦激光介质中泵浦能量的分布情况,模拟不同泵浦结构下泵浦光强在介质中的分布。并以三向泵浦为例,建立热传导方程并对激光介质内的温度分布情况进行模拟。再根据温度梯度与热透镜焦距的关系,得出热焦距随泵浦功率的变化曲线,并介绍了对热透镜效应进行补偿的方法。最后从侧面泵浦情况下泵浦光与振荡光的交叠积分出发,计算了阈值泵浦功率、斜效率和输出功率随不同参数之间的变化关系。2.对几种常用的紫外非线性晶体的特性进行分析,比较各自的优缺点,并针对CLBO晶体与BBO晶体,分析了负单轴晶体Ⅰ类临界相位匹配方式,讨论了不同晶体的相位匹配角、有效非线性倍频系数以及角度相位匹配中存在的一些问题,在讨论晶体允许角时,先利用级数展开的方法计算了晶体的允许角,又根据晶体自身的特点,分析了在主平面内与垂直于主平面的平面内允许角的投影分量,经计算后得出这两种晶体在平行于主平面的平面内允许角远远小于另一个投影分量,从而直接影响着相位匹配的实现与输出的光束质量。最后介绍了CLBO晶体的防潮措施。3.分析了用于倍频的非线性晶体中的相位失配情况;在此基础上给出了平面波近似下与高斯光束下倍频效率的表达式,并分析了倍频效率的影响因素;介绍了聚焦透镜的选择方法;最后分析了非线性晶体温度变化对倍频效率的影响情况。4.在对平-平直腔与平-凹直腔比较分析腔参数对系统稳定性影响的情况下,选择合适的腔型和参数进行实验。首先对绿光生成系统进行调节,在腔长为265mm、电流为45A、重复频率为17kHz时得到了最大输出功率为80W的稳定绿光输出。改变腔型,在系统中引入布儒斯特镜对基频光进行分光,使其实现两路同时振荡,并在其中一路中加入倍频晶体进行倍频,实现了绿光与基频光同时输出。在直腔的情况下,选择合适的聚焦透镜焦距值后先用垂直切割的BBO晶体进行四倍频实验,在泵浦电流为33.2A时获得了607mW的紫外光输出。然后用以布儒斯特角切割的CLBO晶体分别进行了准连续紫外实验,获得了7.1W的266nm紫外光。最后分析了CLBO晶体的切割方式对四倍频效率的影响。更多还原

【Abstract】 Laser diode pumped all-solid-state lasers have many advantages, such as light weight, compactness, efficiency, good beam quality, long life time, and so on. They have been applied in the fields of military, industry, medical treatment, research and communication, and have replaced the traditional lasers, like dye-laser, gas-laser, and so on. The application of laser has been expended by using the nonlinear optical frequency conversion technology. For example, high power solid state green lasers have attracted much attention in numerous applications such as laser medicine, laser display, and so on. The ultraviolet laser with shorter wave length has the unique superiority in precision machining, lithography, high-resolution printing.The main contents of this dissertation are as follows,1. The intensity distribution of multi-side pumped light has been analyzed theoretically, corresponding to different pumping parameters. With the three-side pumped condition, the heat conduct equation has been build up, and the temperature profile in the gain medium has also been simulated. Then the relation between the temperature gradient and the thermal focal length has also been discussed, and the compensation methods of the thermal focal length are provided. At last, we calculate the overlap integral between the pumping light and the oscillating light, and discuss the influence factors of the threshold pumping power and the slop efficiency.2. In this dissertation, the properties of several UV nonlinear optical crystals has been summarized, and some parameters of the negative uniaxial optical crystal has also been calculated, such as phase matching angle, effective nonlinear coefficient, and discussed some problems in the process of angle phase matching. Then the moisture preventive measure of the CLBO crystal has been discussed as well.3. The theories of second-harmonic generation with the plane wave approximation and the focused gaussian beam have been discussed. The selection of the focal length of the focusing lens has also been provided. In the end, we have analyzed the impaction of the temperature change of the nonlinear crystal on the frequency doubling efficiency. 4. After comparative analyzing the impaction of the cavity parameters on the system stability of both plano-plano cavity and the plano-concave cavity, a set of optimal parameters for our experiment has been selected. We then experimentally demonstrate a high power 532nm A-O Q-switched intracavity frequency doubling green laser system in a linear cavity, At incident pump current of 46 A, a maximum QCW output of 80W green laser is achieved. Then we demonstrate a complex cavity that can make the fundamental wave and the frequency doubled wave oscillated simultaneously. On this basis, after focusing the green laser into a type I phased BBO crystal, a UV output at 266nm of 607mW has been achieved with an incident current of 32.2A. Changing the focal length, and use the CLBO crystal to carry on the experiment. At the pumping current of 40A, we get a 7.1W 266nm output using a 70mm focal length of the lens. Finally, we analyze the influence of the cutting way of the CLBO crystal on the conversion efficiency.更多还原