Inhomogeneity in Refractive Index of Evaporated MgF2 Film

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Abstract
By the use of a zero-order approximate formula for reflectance the thickness and inhomogeneity of a transparent film can be determined from angles of incidence for minimum reflectance measured for different wavelengths with p-polarized light. The method was applied to evaporated MgF2 films. The results are as follows. Up to thicknesses of about 1200 Å, the films are homogeneous. For thicknesses from 1300 to 2200 Å, the difference between the refractive indices at the front and rear surfaces of film is less than 0.002, and is undetermined. For thicknesses from 2300 to 6100 Å, the difference is measured as 0.003∼0.034 and increases linearly with film thickness. The refractive index at the front surface of film is larger than at the rear one. The inhomogeneity begins increasing at about 2300 Å.