基于波前探测的高能激光反射镜温度测量技术

Reflective mirrors show a wide variety of applications in high-power laser and it's transmission system. However, thermal effects in mirrors limit the improvement of high-power laser's beam quality. A Shack-Hartmann sensor with thermocouples measurement for the temperature distribution in reflective mirrors is proposed, which overcomes the shortcomings of temperature measurement with thermocoules, thermal camera and interferometric devices. Based on the relationship of wavefront and temperature profile on cross section, temperature can be measured by thermocouples which get the temperature on side face, and Shack-Hartmann sensors which get the temperature profile on the cross-section. Compared with themocouple measurement, it is nonintrusive and can get the temperature profile in each measurement. Moreover, temperature in the area irradiated by high-power laser can be measured with such method. Compared with thermal camera measurement, it is simple and need no calibration before measurement.In addition, it is insensitive to the background infrared radiation. Compared with interferometric technology, the Shack-Hartmann sensor with well-developed algorithm typically operates at a measurement that is much faster and is vibration insensitive. This research is conducive to understanding the thermal effect. Research results can provide a basis for the selection of substrate materials. Wavefront sensors will be able to measure the mirror's real-time temperature and help to guide the deformable mirror to correct the distorted wavefront of high-power laser.

反射镜在高能激光器及高能激光传输系统中有广泛的应用，反射镜膜层及基底材料的热效应问题严重限制了高能激光光束质量的提高。针对常用测温技术（热电偶、热像仪、干涉法）的弊端，提出将哈特曼波前传感器和热电偶相结合的测温方法，原理是：根据波前畸变与温度分布之间的关系，利用哈特曼波前传感器探测的波前信息计算镜片内部通光横截面上的温度差分布，然后结合热电偶测得的镜片侧面温度计算镜片内的温度场分布。与热电偶测温法相比，该方法具有非接触、面测量的优点，并可对高能激光辐照区域的温度分布进行测量。与红外热像仪法相比，该方法使用简单，不需要事先定标，不易受背景辐射的影响。与干涉法相比，H-S 波前传感器对振动不敏感，并且有一套成熟的波前算法，可以进行实时测量。该项目的成功实施，有助于加深对热效应的理解，为高能激光反射镜基底材料的选择提供依据,波前传感器也将可同时实时监控镜片温度，指导变形镜校正高能激光的波前畸变。

随着高能激光输出功率的不断提高，反射镜的膜层和基底材料吸收激光导致的热效应问题日益严重，反射镜的热效应问题已成为制约高能激光技术进一步发展的重要因素。在同时考虑反射镜的膜层和基底材料吸收激光的基础上，课题组提出了一种在有限域上正交的三角函数多项式，基于此多项式推导了高斯激光辐照下镜片温度场分布解析公式；以硅反射镜为例，建立了热效应有限元模型，分析了高斯激光辐照下镜片中的温度场、反射光束波前畸变、透射光束波前畸变的特点，数值仿真结果表明：对于透射光束而言，热光效应和端面变形导致的波前畸变，其幅值虽然不同，但径向分布的线型相同，该线型与热源、弹光效应导致的波前畸变、发射光束的波前畸变的线型均不同。通过哈特曼波前传感器测量了石英高反镜在高能矩形激光辐照下的热变形，并利用ANSYS开展数值模拟计算，计算结果与实验结果具有较好的一致性，验证了数值模型的正确性。考虑到高能激光光束形状不规则，还具有不可预期的时变特性，采用孔径形状函数Mask修正Zernike多项式，实现了在任意形状域内的构造正交基，该正交基可用于任意孔径形状的激光波前重构，仿真实验结果表明该算法具有计算速度快、通用性好、易于推广应用等特点； 针对激光介质为立方晶体或各向同性材料、侧面泵浦的棒状热容激光器，提出了一种计算热致波前畸变和退偏损耗的解析模型，并运用该模型对Nd:YAG、Nd:GGG、Nd:Glass棒状热容激光器中的热效应进行了研究，研究结果表明：同等制冷条件下，若介质中产生的废热相同，Nd:Glass虽然整体温升和径向温差大，但整体波前畸变小；Nd:GGG虽然整体温升和径向温差小，但波前畸变大；Nd:YAG、Nd:GGG与Nd:Glass 中的热致退偏损耗大小相当。本项目对圆柱状介质中的热效应问题进行了较深入的研究，研究成果有助于加深对热效应的认识，对高能激光器反射镜的选型、设计，盘片激光器的热管理优化设计具有一定的指导意义。