Thermal analysis of the laser-induced thermal deformation of a diffractive optical element in a single-aperture coherent beam combining system

Diffractive optical element (DOE) is a critical device for combining multiple laser beams into a single beam in a coherent beam combining (CBC) architecture. This study proposes a determination method for calculating the intrinsic absorption rate of the DOE, and the corresponding experimental system is established. We present a theoretical thermal deformation model of the laser-irradiated DOE based on the thermoelastic equation and thermal conduction theory. The temperature and thermal deformation of the DOE are simulated using different parameters, including the laser power density, substrate size, substrate material, laser incident time, and clamping method. The simulations indicated that the thermal deformation is directly proportional to substrate area and inversely proportional to substrate thickness. The thermal deformation of the DOE can also be decreased by using a two-surface fixing method, and the maximum decrease is 4.4%. The quantitative discussion and analysis of the DOE temperature field and thermal deformation are important for designing a DOE to increase the combining efficiency and improve the combined beam quality of a practical DOE-based CBC system.