22 October 2004 Improved polarization ray tracing of thin-film optical coatings
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Abstract
Thin-film coatings in modern optical systems as wideband AR-coatings may have >10 layers and an optical thickness of several λ. Such complex thin-films may introduce pronounced changes in transmission phases with varying angles of incidence, polarization and/or wavelength. "Polarization ray tracing" as utilized by current optical design programs models a "ray" as a "localized plane wave" hitting the air/thin-film/glass system and the transmission properties in phase and amplitude for the p- and s-components are taken into account. However, this only approximates the thin film as a pure phase object of vanishing thickness on a flat surface. Any "ray" crossing a layer of finite thickness will undergo lateral displacement and on a surface of notable curvature, this displacement will further change the direction of the refracted "ray". Both effects might become important in high NA, deep UV microscope objectives based on an air-spaced design that involves a large number of highly curved air/glass interfaces, large angles of incidence and tight tolerances. This paper shows how the equivalent lateral ray displacement and bending can be calculated from the film/glass properties and the surface curvature and how it can be incorporated into a polarization ray-tracing program. It also addresses other problems encountered in polarization ray tracing of thin films, as proper conversion from phase shifts to optical path length and how to easily "unwrap" the thin-film induced phase.
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Joachim Wesner, Frank Eisenkramer, Joachim Heil, Thomas Sure, "Improved polarization ray tracing of thin-film optical coatings", Proc. SPIE 5524, Novel Optical Systems Design and Optimization VII, (22 October 2004); doi: 10.1117/12.559971; https://doi.org/10.1117/12.559971
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