An absorbing substrate can be coated with a transparent thin film of refractive index N<sub>1</sub> (within a certain range) and thickness d such that the ratio of complex reflection coefficients for the p_and s polarizations of the film-covered substrate ρ = R<sub>p</sub>/R<sub>s</sub> is the inverse of that of the film-free substrate ρ¯ = R¯<sub>p</sub>/R¯<sub>s</sub> at an angle of incidence ø. A method to determine the relationship among ø, <i>N</i><sub>1</sub>, and <i>d</i> that inverts ρ (i.e., makes ρ = 1/ρ¯) for a given substrate at a given wavelength is described and is applied to aluminum and silver substrates at 0.6328- and 10.6-μm wavelengths, respectively. Sensitivity of the inversion condition to incidence-angle and film-thickness errors is analyzed. ρ-inverting layers can be applied to one of the two metallic mirrors of a beam displacer or axicon to preserve the polarization state of incident monochromatic radiation.
© 1984 Optical Society of America
R. M. A. Azzam, "Inverting the ratio of the complex parallel and perpendicular reflection coefficients of an absorbing substrate using a transparent thin-film coating," J. Opt. Soc. Am. A 1, 699-702 (1984)