Continuous gradient multilayer dielectric grating on sapphire substrate for high-power spectral beam combining

Diffraction gratings employed in high-power spectral beam combining systems exhibit significant thermal effects under extreme laser irradiation. The resultant temperature rise on the grating surface degrades beam quality, posing a major challenge for enhancing system performance. This work uses a finite element model to simulate the temperature distribution on the grating surface under various laser irradiation conditions. A new grating design strategy is proposed, utilizing a highly thermally conductive sapphire substrate integrated with a continuous gradient multilayer dielectric grating (CGMDG) structure. Gratings fabricated based on this design demonstrate superior thermal stability. Experimental results show that the temperature increase on the grating surface remains below 1°C even under laser irradiation at power densities up to 71.66 kW/cm².