Intrinsic birefringence in calcium fluoride and barium fluoride

We report measurements of the intrinsic birefringence in CaF2 and BaF2 for wavelengths in the range 365 nm to 156 nm, and ab initio optical response calculations in these materials and Si, Ge, GaAs, and GaP. Calculations typically agree within 40%. For [110] propagation, where the effect is largest, our measurements for CaF2[BaF2] give n([(1) over bar 10])-(n[001]) (- 11.8 +/- 0.4) x 10(-7)[(+ 34 +/- 3) x 10(-7)] for lambda = 156.10 nm. The magnitudes of these values have serious consequences for them use of crystalline optics in precision optical systems in the ultraviolet, including 193 nm and 157 nm optical lithography.