Thermal Lensing in Infrared Laser Window Materials

A theoretical investigation of thermal lensing in infrared windows is presented which treats aberration effects to all orders in the small angle-of-deviation approximation. The model is applied to a truncated Gaussian infrared laser beam incident on a semitransparent isotropic disk-shaped window. It is shown that window aberrations limit the time a diffraction-limited focus can be held in the far field. This diffraction-limited time td is computed for some candidate window materials and their relative merits are discussed.