Abstract
The refractive index n1 of a transparent layer of quarter-wave optical thickness coating a transparent substrate of refractive index n2 can be chosen to produce half-wave retardation (HWR) in reflection and no change of polarization in refraction at any angle of incidence ϕ. The function n1(ϕ, n2), and the associated polarization-independent reflectance of the film-substrate system are determined. Such a coated surface can be used as a beam splitter with excellent characteristics (e.g., split fractions that do not depend on source polarization, a split beam whose polarization is identical to that of the incident beam and operation over a wide range of incidence angles). A concrete example of a coated Ge-slab beam splitter for 10.6-μm radiation at ϕ = 45° is given. The beam-splitter face of the slab is coated with the HWR layer, and the exit face is coated with a double layer that produces total refraction without change of polarization. Such a beam splitter is tolerant to film-thickness errors and is reasonably achromatic over a small (e.g., 10–11-μm) wavelength range. When used in a Michelson interferometer this beam splitter renders its operation totally independent of source polarization.
© 1986 Optical Society of America
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