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ELLIPSOMETRY METHOD APPLICATION IN OPTICS OF INHOMOGENEOUS MEDIA

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Physico-mathematical methods of modeling and measurements of polarization optical characteristics of “inhomogeneous surface layer – inhomogeneous medium” reflective system have been improved based on generalization of the polarized light reflection theory in the Born approximation from inhomogeneous media interface. Theoretical and experimental justification for simultaneous application of multi-angular and scanning ellipsometry methods is given for gradient optics elements in inhomogeneous layer presence on the surface of the optical detail. The measurement of the main ellipsometric parameters – linear reduced polarization azimuth Ψ and phase difference Δ between mutually orthogonal p– and s– components of a reflected polarized light beam – was carried out on a dual-channel installation, in which the scheme of measurements of polarization parameters Ψ and Δ by balanced (null) ellipsometry method is used in the first channel; the photometric scheme of measurements of parameters Ψ and Δ by Fourier method of output detection is used in the second channel. Such separation of channels gives the possibility for measuring of polarization  parameters of reflected light beam separately and, thereby, improving the accuracy of ellipsometric measurements in relation to observable physical quantity of measurements object. The values of refractive index n(r) and absorption index k(r) were calculated by axial section of selfoc on the basis of measurements of polarization parameters Ψ and Δ with angle of incidence of the light beam φ=45о within the limits of scanning ellipsometry method and a model of geometrically flat interface of homogeneous media. Empirical data indicated the model incorrectness of the geometrically flat interface for polarization measurements of refractive index distribution n(r) and absorption index k(r) in gradient optical engineering elements. For the reflective system “inhomogeneous surface layer – inhomogeneous medium” the refractive index n(r) change by axial section of an element r is proportional to phase difference Δ(r) between mutually orthogonal components of a reflected light beam. At the same time the linear reduced polarization azimuth Ψ(r) in the section gradient optical element varies slightly. The main proportions for calculation of refractive index nс and thickness dс of superficial layer in each local point r of selfoc are adduced on the basis of the ellipsometry equation, obtained within the framework of the polarized light reflection Born theory. Empirical data of experimental researches make it possible to give quantitative assessment of surface processing quality for optical engineering elements. Elaborated ellipsometric techniques are recommended in technological production of optical base assemblies with gradient and fiber optics elements.

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