Theoretical investigation of interaction between 3.8µm laser and fused silica based on the measurement of temperature dependent absorption coefficient

The absorption coefficient of fused silica in the mid-infrared (IR) range lies between those at near-IR and far-IR wavelengths. Consequently, mid-IR lasers offer both high energy coupling efficiency and deeper penetration depth, providing a significant advantage for laser repair of optical component damage. In this study, an experimental setup was established to measure the temperature dependent absorption coefficient of fused silica at a wavelength of 3.8 µm. The experimental results indicate that the absorption coefficient of fused silica at 3.8 µm increases linearly with temperature. When the temperature reaches 2000 K, the absorption coefficient increases to 1004 m^-1, approximately 1/200 of the absorption coefficient at 10.6 µm. Furthermore, based on the measured absorption coefficient, a simulation model for the interaction of 3.8 µm laser with fused silica was established. The simulated ablation morphology is in good agreement with reported experimental results, and the variation in the reflected signal corresponds to the increase in material temperature to the softening point, as well as the retreat of the air-liquid interface.