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In this paper, the theoretical analysis of the correctness of applying the effective medium approximation (EMA) at the ellipsometric studies of rough surfaces is presented. Within this analysis the Rayleigh–Rice theory (RRT) is used to calculate the simulated ellipsometric data of various slightly randomly rough surfaces. This simulated data are treated using the least-squares method for finding the values of the parameters characterizing the rough surfaces within the EMA, i.e., the values of thickness and packing density factor describing a fictitious (effective) thin films replacing these surfaces within the EMA. It is shown that the EMA could be used to interprete the ellipsometric data of the rough surfaces in a correct way if their roughness only contains the high spatial frequencies. For the low spatial frequencies it is shown that the influence of the surface roughness on the ellipsometric quantities is small in contrast to its influence on the reflectance. Moreover, it is shown that the EMA must be used carefully for optical characterizing rough surfaces and that it is more reasonable to use the RRT for this purpose. It is also presented that in general it is impossible to expect a good agreement between the thickness values determined using EMA within the ellipsometric analysis and the rms values of the heights of the irregularities evaluated by atomic force microscopy (AFM) for the same rough surfaces.

In this theoretical paper the basic statistical quantities of the light intensity above thin-film systems with randomly rough boundaries are studied in the near-field. This means that formulae for the mean intensity, standard deviation of the intensity, correlation function of the intensity and the speckle contrast are derived for the systems mentioned in the near-field. It is assumed that the boundaries of the systems are slightly rough, i.e. that the rms values of heights of the irregularities of the boundaries are much smaller than the wavelength of incident light. The Rayleigh-Rice approach is employed for deriving the formulae expressing the quantities specified. In conclusion a brief numerical analysis of the theoretical results is presented.

In this theoretical paper new formulae for calculating the specular reflectance of multilayer systems with randomly rough boundaries are presented. These formulae are derived within the scalar theory of diffraction. They are suitable for investigating the multilayer systems with slightly rough boundaries. The theoretical results are illustrated through the spectral dependence of the reflectance characterizing a multilayer system formed by seven nonabsorbing films.

The reflection of light on a system of non-absorbing isotropic film-non-absorbing isotropic substrate with both boundaries (air-film and film-substrate) rough as well as some special cases of this system are considered. The formula for the coherent component of reflected light intensity has been derived. The agreement of theory with experiment is excellent in the case of an identical thin film (air-film boundary perfectly reproduces the rough film-substrate boundary).

The influence of the surface roughness on the ellipsometric parameters Δ and ψ is considered. The Helmholtz-Kirchhoff integral has been chosen as a starting point. Having used several simplifications (justified for slightly rough surfaces) we derived the equation representing a definition of Δ and ψ in the case of an isotropic material with rough surface.

Considering some simplifying assumptions (especially a moderately rough surface) we present a method for calculating the ellipsometric parameters δ and Ψ characterizing a randomly rough surface. The Stratton-Chu-Silver integral has been used in our approximation. We present also a comparison of the present results with those obtained earlier by means of the Kirchhoff scalar theory.