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, disc-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 computer for some candidate window materials and their relative merits are discussed. Some approaches to solving the thermal lensing problem from both an engineering and a materials point of view, as well as some program research and development needs, are discussed.