Intrinsic birefringence in calcium fluoride and barium fluoride
Abstract
We report measurements of the intrinsic birefringence in ${\mathrm{CaF}}_{2}$ and ${\mathrm{BaF}}_{2}$ 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 ${\mathrm{CaF}}_{2}[{\mathrm{BaF}}_{2}]$ give ${n}_{〈1\ifmmode\bar\else\textasciimacron\fi{}10〉}\ensuremath{-}{n}_{〈001〉}=(\ensuremath{-}11.8\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}[(+34\ifmmode\pm\else\textpm\fi{}3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}]$ for $\ensuremath{\lambda}=156.10\mathrm{nm}.$ The magnitudes of these values have serious consequences for the use of crystalline optics in precision optical systems in the ultraviolet, including 193 nm and 157 nm optical lithography.