Grating absorption is a phenomenon influenced by various factors such as material properties, grating structure, and characteristics of the incident light. Under intense laser irradiation, the absorbed energy of the laser is converted into thermal energy, resulting in an elevated temperature of both the grating and substrate. This temperature rise significantly compromises the optical performance of the grating, thereby imposing constraints on the advancement of high-power laser systems. The numerical simulations were performed using the finite element method to investigate the effects of different absorptivity of grating, spot sizes, substrate materials (Fused silica, BK7 and Sapphire), and convective coefficients of air on the temperature distribution at various locations on the substrate under high-power laser irradiation (30kW/cm2). Comparative analysis reveals that selecting sapphire as the substrate material under high-power laser irradiation results in better heat dissipation.
The diffraction characteristics of amplitude and phase-type soft-edge apertures with super-Gaussian transmittance at the gap of mosaic grating are investigated in this article. A well-designed soft-edge apertures can effectively suppress the Fresnel straight-edge diffraction intensity distribution at a certain transmission distance and consequently homogenize the overall light intensity on the image plane. We use the PV value, which is the difference between the maximum intensity of Fresnel diffraction and the initial incident intensity, as the evaluation index of diffraction intensity homogenization. Compared with use of the hard-edge aperture, the PV value reduces from 0.6 to 0.009 and 0.051 at the distance of 0.5m and 1m respectively with use of the super-Gaussian amplitude type soft-edge apertures designed by us. While using the super-Gaussian phase type soft-edge apertures designed by us, the PV value reduces from 0.6 to 0.053 and 0.06 at the distance of 0.5m and 1m respectively.
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