“Analytical Model for Evaluating Transient, Steady-State, Coating Damage Threshold, Optical Distortion, and Axial Gradient for Externally Cooled Laser Mirrors.”

Abstract

There are a number of requirements in high energy laser systems to provide optical elements that are not integrally cooled. However, there are many instances where a cooling gas, such as helium or nitrogen, may be used to cool the front and back surfaces in order to reduce optical distortion. In order to evaluate the response of an optic to this type of cooling, first order analytical techniques have been generated to determine transient and steady-state temperature distributions through a fully irradiated optic, an irradiated spot on a large optic, and a toroidal shaped beam (i.e., hole in the beam), on a large optical element. Cooling temperatures and damage relationships coupled with optical path differences of the flowing gas are treated for evaluation. Optical distortion of the element due to radial and axial temperature gradients are treated for both transient and steady-state conditions and for various gas flow dynamics.