The important sources of optical loss in the Brewster windows of a gas laser are outlined, and the effects of this loss on the performance of the laser are described. Particular attention is paid to thermal focusing effects which occur when absorbing films are formed on the Brewster windows of high-power lasers. A semiquantitative theory is developed which shows that absorptive loss in the windows sets an upper limit on the intracavity intensity of a Brewster window laser.
D. C. Sinclair, "Optical Loss and Thermal Distortion in Gas-Laser Brewster Windows," Appl. Opt. 9, 797-801 (1970)