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

ABSTRACT 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.