Influence of cooling strategies on thermal stress evolution in multilayer dielectric films

Traditional mirror coating processes are generally associated with high film stress and poor environmental durability of metallic layers, which can lead to reduced yield and increased production costs. To optimize mirror coating techniques, this study developed all-dielectric high-reflectivity films on quartz substrates, covering the 0.532 μm, 1.064 μm, and 3.7–4.8 μm wavelength bands. Appropriate high- and low-refractive-index coating materials were selected to establish a 3D multiphysics finite element model integrating thermal and stress fields, thereby investigating stress distribution characteristics between the quartz substrate and the thin films. Guided by the simulation results, the deposition process was optimized through in-situ vacuum gradient cooling annealing, effectively relieving the residual stress and preventing film delamination. The average reflectivity across the target wavelength bands reached 98.68%, meeting the engineering requirements for laser beam expander applications.