不同夹持方式下不同高反膜系腔镜的热形变分析

Analysis of Thermal Distortion of Resonator Mirror with High Reflective Coatings in Different Clamping Ways

在研究高功率激光辐照下激光器腔镜表面热形变分布时通常会忽略其表面镀有的高反射膜系。利用有限元分析软件ANSYS比较了特定激光辐照(吸收功率250W,外环半径4 cm、内环半径2 cm的同轴环形光束,30s)下的高反腔镜在不同夹持方式下的热形变分布,同时考虑了腔镜表面镀有的两种不同高反膜系及膜系中的驻波场的影响,并与通常忽略膜系的情况进行了对比分析。研究表明,采用压圈法时,三种情况下热形变分布的差异相对较小;采用压板法时,三者形变分布产生了明显的差异,镜面中心可能上凸、下凹或者平缓;采用三点法时,尽管镜面中心热形变分布较为平缓,但在环状光束辐照区域内三者仍有明显差异。因此,膜系内驻波场对腔镜热形变分布的影响不能轻易忽略。

In the study of thermal distortion of resonator mirrors under high-power laser irradiation, the high reflective coatings are usually ignored. The thermal distortion distributions of resonator mirrors with high reflectivity fixed in different ways are analyzed by finite element analysis software ANSYS under the specific laser irradiation （absorbed power of 250 W, outer radius of 4 cm, inner radius of 2 cm, co-axial annular beam, 30 s）. The effects of two different high reflective coatings and the field distribution of standing wave inside the coatings are considered, and the results are further compared and analyzed with the usual approximate method that the high reflective dielectric coatings are ignored. The results show that, the difference of thermal deformations among the three situations, i.e., considering two different high reflective coatings and ignoring the high reflective coatings, is relatively small when the resonator mirror is clamped radially. However, the difference becomes obvious when the resonator mirror is clamped axially and the center of the mirror can be convex, concave and flat. If the resonator mirror is fixed by three cones, though the center of the mirror can be relatively flat, there is still obvious difference among the three situations in the irradiation zone of the annular laser. Consequently, the contribution of the standing wave inside the high reflective coatings to the thermal distortion of resonator mirrors cannot be ignored in some applications.