Laser window materials: an overview

The laser window problem is reviewed with emphasis on failure mechanisms, absorption processes, and material evaluation. Failure by thermal fracture and by optical distortion is discussed and the material parameters needed to calculate figures of merit for these failure modes are tabulated for a variety of materials. The exponential dependence of absorption coefficient on wavenumber for intrinsic multiphonon processes is discussed and its use in discriminating extrinsic from intrinsic absorption emphasized. Laser calorimeter absorption measurements at 10.6 and 5.25 μm are described and the measured values tabulated. The use of internal reflection spectroscopy to examine the effect of various surface treatments on surface absorption is discussed. The absorption of most KCl crystals at 10.6 μm is shown to be impurity dominated