Optical Properties of Lithium Fluoride in the Extreme Ultraviolet

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Abstract
The absorption coefficient of lithium fluoride in the extreme ultraviolet was measured for 50 crystals produced in the laboratory. The variation in the absorption coefficients for the different crystals was almost as great as that found in natural fluorite although the individual specimens seemed more homogeneous than natural crystals. Numerical values of the absorption coefficient are given for the best specimen. The light lost from the transmitted beam on passing through a surface was studied for cleavage and polished surfaces. At short wave-lengths the loss of light was much greater than that expected for specular reflection. Tests with various cleaning agents indicated that at least a part of this loss of light was due to a layer of foreign material adhering to the surface. Considerable gain in transmission especially at short wave-lengths was obtained by careful cleaning of the polished surfaces with a highly volatile solvent followed by heating to a temperature just below red heat. The index of refraction curve for lithium fluoride was extended into the Schumann region by a modified minimum deviation method.