Study on the influence of thermal deformation of dichroic mirrors on laser beam quality under high-power continuous laser irradiation

To address the issue of beam quality deterioration caused by the thermal deformation of dichroic mirrors (DMs) in high-power laser systems, this paper establishes a thermal deformation model of DMs under high-power laser action based on the theories of laser transmission and three-dimensional heat conduction. The distribution laws of the temperature field and thermal deformation are analyzed, and the process by which the deformation affects the beam distortion is elucidated. Finally, a real-time testing device is set up to reveal quantitative relations of temperature, deformation and beam quality. The results show that when the DM's thermal deformation peak to valley (PV) < 120 nm and root mean square (RMS) < 30 nm, the beam quality can remain good without significant deterioration. Furthermore, it is found that the substrate's thermal expansion coefficient mainly affects DM deformation and beam quality. The research provides theoretical basis and data support for the component thermal effect control.