高功率Nd:YVO_4/KTP腔内倍频晶体温度分布的半解析热分析

Semi-analytical thermal analysis of high power Nd:YVO_4/KTP intracavity doubling crystal

非线性晶体KTP采用Ⅱ类相位匹配腔内倍频时,不仅要求晶体满足基频光的偏振匹配条件,而且所选用的晶体要求符合λ/2波片的条件,才能使晶体的谐波转换效率达到最佳。由于倍频晶体吸收基频光能量引起晶体内部非均匀温升,改变晶体内部各点的折射率,也会使晶体产生不应有的热形变,破坏晶体初始的位相匹配条件,严重影响输出激光的品质和倍频效率。减弱、改善这种情况的关键是准确得出在实际工作条件下晶体内部温度场。利用半解析热分析方法得出了KTP晶体内部温度场的计算方法,分析了各种热参量变化对KTP晶体内部温度场的影响。得出的结果具有一定的普适性,可以应用到具有轴对称形式内热源的其它热模型温度场的计算分析中,对连续波腔内倍频激光系统的设计将起到指导作用。

In diode-pumped all-solid-state laser system, nonlinear optical double frequency crystal KTP, which cut at Ⅱ-type phase match condition, not only oriented satisfied with fundamental light's polarization condition, but also met its with half wave plate condition, and only these conditions are all fulfilled, crystal would have the maximal harmonic conversion efficiency. But double frequency crystal, which is absorbed fundamental light radiation, would induce crystal interior non-uniform temperature raise. Subsequently the thermal phenomenon will cause crystal 's refractive index changed, and will induce crystal generated thermal distortions, all these phenomena would destroy nonlinear crystal intrinsical phase-matching-condition, affect output laser's quality and double frequency conversion efficiency. To diminish and improve this situation the key work is to obtained accuracy crystal working condition's temperature distribution. KTP crystal interior temperature field is obtained by semi-analytical thermal analysis method, and all kinds of relevant parameters, which influenced temperature field distribution, are analyzed. The analysis method and research results have ordinary applied character. This solution can also be applied to analysis those model which have axis-symmetrical and inner heat source or other thermal models. These works will play instructive effect at the optimum design of continuous wave intracavity double frequency laser system.