Infrared stress birefringence in KBr, KCl, LiF, and ZnSe

The application of a variation of intensity method using static stress and polarized light to measure stress birefringence in the infrared wavelength region (∼4−11 μm) is described. We have used this method to measure the stress optic coefficient Cλ for the alkali halide cubic crystals KBr, KCl, LiF, and polycrystalline ZnSe. A detailed discussion of the definition of Cλ in terms of piezo−optic coefficients is given in the paper. Our results indicate that no wavelength dependence is observed for Cλ in the 4−11−μm region for KCl and KBr which have typical measured Cλ values of +3.3 and +3.4 Brewsters, respectively. For LiF at 8 μm we get Cλ=−3.08 Brewsters and for ZnSe we obtain Cλ values of −13.2 Brewsters at 9.4 μm and −13.0 Brewsters at 11 μm.