Analysis of thermal stresses in HfO2/SiO2 high reflective optical coatings for high power laser applications

HfO2/SiO2 high reflective optical coatings are widely used in high power laser applications because of their high laser damage resistance and appropriate spectral performance. The residual stresses strongly influence the performance and longevity of the optical coatings. Thermal stresses are the primary components of the residual stresses. In the present work, the distribution of thermal stresses in HfO2/SiO2 high reflective optical coatings was investigated using two different computational methods: finite element method (FEM) and an analytical method based on force and moment balances and classical beam bending theory. The results by these two methods were compared and found to be in agreement with each other, demonstrating that these two methods are effective and accurate ways to predict the thermal stresses in HfO2/SiO2 optical coatings. In addition, these two methods were also used to obtain the thermal stresses in HfO2/SiO2 optical coatings with different layer number to investigate the effect of the layer number on the thermal stresses of the HfO2/SiO2 optical coatings. The results show that with the increase of the layer number, the stresses in the substrate increase, while the stresses in the respective SiO2 and HfO2 layers decrease. Besides, it was also found that the radius of curvature of the coating system decreases as the layer number increases, leading to larger bending curvature in the system.

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