Measurement of the absorption coefficient of silica glass in the near-infrared range

Subject of study . The absorption coefficient of fused silica plates is investigated. Aim of study. The aim is to measure the absorption coefficient of fused silica at a wavelength of 793.4 nm and investigate the spatial nonuniformity of the absorption coefficient within the aperture of optical samples. Method. The absorption coefficient is measured using a photothermal method with a Shack–Hartmann sensor. The measurement technique is based on monitoring the wavefront of radiation transmitted through a sample subjected to local thermal loading induced by laser irradiation, followed by the creation of a digital twin of the sample. Numerical simulations of the heating and deformation processes in the samples are performed using the finite-element method. The relative measurement error is 20%. Main results. The mean absorption coefficient of the three samples ranges from 0.6×10 ⁻⁵ cm ⁻¹ to 1.5×10 ⁻⁵ cm ⁻¹ . One of the samples exhibits pronounced spatial nonuniformity of absorption. In this sample, the ratio of the maximum to minimum absorption is 1.7. Practical significance. The obtained results can be used for the calculation of thermal aberrations in near-infrared laser optical systems employing optical elements composed of fused silica.