Refractive indices and extinction coefficients of lithium fluoride in thin film coated at room temperature are deduced from reflectance curves from 100 to 120 nm. These refractive indices are smaller but approximately follow the same dispersion law as crystalline LiF indices. The extinction coefficients are of the order of 0.1, i.e., 10<sup>5</sup> times higher than those of crystalline LiF. The absorption by the low-energy tail of an exciton band has been represented by the Urbach rule. These complex refractive indices have been used to optimize the first-order efficiency of LiF-coated Al gratings of the NASA FUSE (Far Ultraviolet Spectroscopic Explorer) space mission.
© 2000 Optical Society of America
(120.4530) Instrumentation, measurement, and metrology : Optical constants
(160.4760) Materials : Optical properties
(260.7210) Physical optics : Ultraviolet, vacuum
(310.0310) Thin films : Thin films
Véronique Dauer, "Optical constants of lithium fluoride thin films in the far ultraviolet," J. Opt. Soc. Am. B 17, 300-303 (2000)