The optical constants of thin films of MgF2, LaF3, and CeF3 have been determined in the spectral range of 30-950 nm. Among them, MgF2 is a low refractive index material whereas LaF3 and CeF3 have a relatively high refractive index at short wavelengths; this contrast is adequate to make multilayer coatings. Fluoride thin films were deposited by evaporation onto substrates at 523 K. Optical constants were calculated using sets of transmittance, reflectance, and ellipsometry measurements. The measured optical constants were extended to a broader range with literature data and extrapolations in order to obtain self-consistent sets of data using the Kramers-Krönig analysis. The optical constant data here presented extend the available literature data both shortwards and longwards, particularly for CeF3 where few data had been reported.
The obtained optical constants of MgF2 and LaF3 were used to design narrowband reflective multilayer coatings for the short FUV. Multilayer coatings centered at 121 and at 130 nm with remarkable reflectance were prepared. The coatings kept a valuable reflectance after ageing in a desiccator for 12 months.