Numerical simulation of the thermal lens effect in an optical system generating powerful near-IR radiation

A thermal lens in an optical system generating powerful continuous radiation in the near-IR range (λ = 1.07 μm) is investigated. The objective of the work is to select a material for manufacturing elements of a bench optical system being developed for investigations of the destruction threshold of optical materials by continuous laser radiation, based on results of numerical modeling of the thermal lens effect. N-BK7 optical colorless glass, Suprasil synthetic fused quartz, and calcium fluoride (CaF2) are considered as the material of the optical elements. The processes of heating and deformation of the optical elements are modeled using the finite element method. Using the ray tracing method, the analysis of beam wavefront distortions is performed and defocusing is calculated. The contribution of thermal deformations of the working surfaces of the elements and the temperature change in the refractive index of the material to the distortion of the wave front of transmitted radiation is analyzed. The effect of thermal aberrations on the size of the working beam is analyzed. The obtained results can be useful in selecting optical materials for elements of optical systems of high-power lasers.