高功率密度激光辐照下镀膜镜片热变形的模拟和测量

Modeling and Measurements of Thermal Deformation of Coated Mirror Irradiated by High Intensity Laser

为研究近红外高功率密度激光辐照下熔融石英镜片的热变形,基于有限元分析软件建立了镜片热力学模型并进行了计算分析,同时开展了实验测量。首先,建立了镀增透膜楔形石英镜片的有限元分析模型,得到了激光辐照下温度和形变量随时间的变化关系和镜体形变图像。其次,计算分析了楔镜体吸收率、膜层吸收率对热变形的影响,研究了不同功率密度和总功率的激光辐照时熔融石英镜片热变形的规律。最后,研究了镀增透膜石英楔镜在总功率为12 kW和最高功率密度为44 kW·cm^(-2)激光辐照下的温升和形变规律,并对实验和建模计算结果进行了分析,激光功率在5~15 kW范围时,面型计算值与实验测量值最大相对偏差约为6%。激光功率在2~15 kW范围时,温度计算值与实验测量值最大相对偏差约为8%。研究结果表明:热变形主要取决于膜层的吸收,楔镜的温升和形变量随膜层吸收和体吸收率呈准线性变化关系;膜层吸收和体吸收形变方向的不同可能造成面型凹坑。

To study the thermal deformation of fused silica mirror under high intensity laser radiation,a mirror thermodynamics model based on the finite element method was built and experimental measurements were performed.Firstly,a finite element model for anti-reflection(AR)coated silica mirror was established,and characters of temperature changing and mirror deformation with different irradiation time were calculated and shown.Then the effects of bulk absorption and coating absorption on the thermal deformation of fused silica mirror were calculated.And the regular patterns thermal deformation under different laser intensity and power were obtained.Finally,we demonstrated an experiment in which a silica wedge with AR coating was irradiated with a total power of 12 kW and a maximum power density of 44 kW·cm^(-2).Both the temperature rising and the deformation were measured,and these results were compared with the simulated ones.When the laser power was 5~15 kW,the calculated deformation had a difference of maximum to 6%to the measurement result.And when the laser power was 2~15 kW,the calculated temperature had a difference of maximum to 8%to the measurement result.The research indicates that the thermal deformation is mainly caused by coating absorption,and temperature rising and displacement would linearly vary with the bulk and coating absorption factors.The different vectors of thermal deformations caused by coating absorption and bulk absorption respectively would lead to the concaves on the surface.