Spectral‐Integrated Thermal Absorption Model for Broadband Laser‐Protective Reflectors Under Supercontinuum Irradiation

With the advancement of high-power multiwavelength lasers, their intense power density causes severe thermal damage to high-value targets. Nanometer-scale multilayer coatings with high reflectivity offer a promising means of protection. However, research on their thermal responses under multiwavelength irradiation and broadband protection remains limited. To address this issue, a novel universal laser-energy absorption model based on spectral intensity integration is proposed for nanometer multilayer coatings. Based on this model, we designed ultrabroadband all-dielectric nanometer multilayer reflectors with a theoretical average reflectance greater than 99.9% in the 450-1200 nm range, and we experimentally evaluated their temperature under supercontinuum laser irradiation. The proposed energy-absorption model reveals that the energy absorption in reflectors under laser irradiation follows an exponential decay behavior, which is distinctly characterized by two absorption coefficients. The contribution of short-wavelength absorption to temperature rise exceeds that of long-wavelength absorption. Therefore, a short-wavelength-prioritized reflector exhibits the smallest temperature increase and can be effectively leveraged for broadband laser protection. The new model allows efficient temperature-rise simulations of reflectors under laser irradiation using the finite-element method, with simulation results showing good agreement with the experimental data. These findings provide valuable insights for thermal evaluation of laser-protective reflectors.