A reflectometer adaptable to the exit slit of a grazing-incidence monochromator is developed to investigate the optical properties of crystals or evaporated layers before exposure to air in the region 100–1000 Å (124–12.4 eV). The optical constants are determined by three methods; one of them is new and based on the state of polarization of the light emerging from the monochromator. The real and imaginary parts of the dielectric constant and the energy-loss function (-Im∊<sup>-l</sup>) are given for Pyrex, corundum, and ruby and for polished and cleaved crystals of LiF and CaF<sub>2</sub>The possibility of a plasma level is discussed from experimental curves.
GUY STÉPHAN, JEAN-CLAUDE LEMONNIER, and SIMONE ROBIN, "Optical Properties of Insulators in the Extreme Ultraviolet," J. Opt. Soc. Am. 57, 486-492 (1967)