Birefringence minimizing fluoride crystal optical VUV microlithography lens elements and optical blanks

The present invention relates generally to optical lithography elements and blanks, and particularly to optical microlithography crystal lens elements and optical element blanks for use in optical photolithography systems utilizing vacuum ultraviolet light (VUV) wavelengths below 200 nm, preferably below 193 nm, preferably below 175 nm, more preferably below 164 nm, such as VUV projection lithography systems utilizing wavelengths in the 157 nm region. A birefringence minimizing fluoride crystal vacuum ultraviolet ("VUV") optical lithography lens element is provided for use with lithography wavelengths