Vacuum-ultraviolet refractive index of LiF and MgF_2 in the temperature range 80–300 K

The refractive indices of LiF and MgF2 have been measured with an accuracy better than ±0.003 from 200 nm down to their respective cutoff wavelengths for various temperatures ranging from 80 to 300 K. For LiF, the temperature coefficient changes sign at 160 nm. The data were fitted to a two-term dispersion equation. The corresponding oscillator strength values for the exciton peak (0.45 and 0.69 for LiF and MgF2, respectively) are in agreement with existing data.