The experimental setups have been built in the use of the photothermal deflection technology and surface thermal lensing technology , respectively . the weak absorption of different optical thin films has been measured . the experimental results obtained from the above two methods were compared 4 .分别建立了表面热透镜技术和光热偏转技术测量光学薄膜微弱吸收的实验装置，对多种光学薄膜样品的微弱吸收进行了测量，并将两种方法测得的实验结果进行了比较。
But the absorption efficiency , stokes efficiency , quantum efficiency and the superposition efficiency between pump mode and cavity mode is less than one respectively , so the local heat absorption of the crystal is quite strong , and its thermal effect is quite obvious . two measures were taken 但是，由于量子效率小于1 ，斯托克斯频移，泵浦光与基模的非完美空间重叠以及激光晶体的偏振吸收等因素积聚在晶体内的热量随泵浦辐射而变化，出现更为复杂和明显的热透镜效应。
However , traditional methods , including spectrophotometric , extinction coefficient method , are not sensitive enough to measure absorption of thin films in the 10 ~ ( - 4 ) 10 ~ ( - 7 ) range which is often used in the modern optical system . surface thermal lens ( stl ) technique was developed by kuo and saito respectiv - ely in the early 1990s 光热技术的发展为光学薄膜微弱吸收测量提供了新的手段,表面热透镜技术( stl )作为光热技术测量光学薄膜微弱吸收的一种重要方法,在上世纪九十年代初,由kuo和saito分别提出。
In this paper , the stl technique with cw modulated top - hat beam excitation is investigated theoretically and experimentally . 1 . the theoretical model based on the fresnel diffraction integral is developed to describe the stl signal excited with the cw modulated top - hat beam for the first time to the best of our knowledge 本论文提出采用连续调制的平顶光束作为激励光的表面热透镜技术测量薄膜吸收的方法,主要开展了如下工作: 1 .建立了连续调制的平顶光束作用下样品的表面热透镜信号模型。
Based on the rate - equation theory of four - level system , the expressions of threshold pump power , output power and slope efficiency are given . the influence of space distribution of pump light ( the position of focusing point , dimension of pumping light and divergence angle ) to the output characteristics are also discussed . then , by investigating the effects of thermal effect of laser crystal on the size of laser cavity mode , we obtain the mode - matching principle of high power laser diode end - pumped solid - state lasers 其中，在泵浦光的空间分布变量中我们分别考虑了泵浦光聚焦后的腰斑大小、聚焦腰斑在增益介质中的位置以及泵浦光在介质中发散角的影响；然后我们研究了在高泵浦功率下激光晶体因吸收泵浦光而产生的热效应所导致的热透镜效应以及热致衍射损耗，通过分析它们对振荡激光腔模尺寸的影响，得到了高功率半导体激光二极管端面泵浦固体激光器模式匹配的要求，为高功率连续单频nd ： yvo _ 4激光器的优化设计提供了理论依据。
Because of high threshold of 946 nm laser , severe thermal lens effect will appear when the 946 nm laser operations . in the consideration of thermal lens effect , the - optimized folding cavity has been devised . the relation between thermal lens effect and the radius of laser beam waist has been given as well 由于946nm激光阈值很高，需要更强的泵浦功率密度，因此较大功率蓝光激光器的热透镜效应将会比红光和绿光激光器更明显，而热透镜效应是影响激光功率提高和激光输出稳定性的重要原因，所以在考虑到激光晶体热透镜效应的情况下，优化设计了折叠腔结构，并给出了热透镜效应和折叠腔中腔模半径大小的关系。
First , some principle that should be considered in building a laser cavity was discussed based on the rate equation of four - level laser model . then , the thermal lens effect of nd : yvo4 crystal was analyzed and estimated theoretically . the laser cavity was designed by considering the thermal lens effect and the optimal transmission was estimated 首先在理论上通过四能级激光器速率方程，讨论了激光器设计上需要注意的一些原则，然后分析了nd ： yvo _ 4晶体的热透镜效应，理论上估算了其热焦距的大小，并且在腔型设计中给予了考虑。
In former stl instruments , a laser beam with a gaussian distributed intensity was commonly used as the excitation source . nevertheless , the output of a high power laser is usually a superposition of multi - modes rather than a gaussian distribution ( tem00 ) . therefore , it is very convenient to add an aperture to get a top - hat beam 以前的表面热透镜装置中,多使用高斯光束作为激励光,但由于高功率激光器一般为多模输出,要获得严格的基模高斯光束比较困难,而平顶光束可以通过在激光器前加一定大小的光阑实现,降低了对激光光束质量的要求,更有利于实际的测量。
