Plane-polarised light which is incident on a surface, when reflected and refracted, acquires elliptical polarisation due to a thin transition layer at the interface, and this layer’s optical constants control the parameters of elliptical polarisation.

The main application of ellipsometry is to determine the optical constants of thin films (e.g., oxide thin films), as well as their thickness in the range, which is significantly smaller than the wavelength of light. Ellipsometry acquired more interest in 1970-80s because emphasis was given to structure analysis, physical and chemical property studies and surface inspection since those data were important for rapidly developing solid-state electronics (primarily the semiconductor electronics). Ellipsometry is also used to study adsorption in a high vacuum on flat metal surfaces, polymer adsorption at the liquid-gas and liquid-liquid interface, catalytic processes at the micro level, the properties of the surface upper layers exposed to corrosion, to study the oxidation of electrodes in electrochemistry, and to study cell walls and lipid membranes in microbiology, etc.

The advantages of ellipsometry are simple and fast measurements (there are automatic ellipsometers), it is possible to make in situ measurements, in vacuum, at high temperatures, in aggressive environments; in addition, the experiments do not contaminate or disintegrate the surfaces. The main drawback of the method is that it is not easy to select the proper reflecting system model and interpret the results. Therefore, most promising is the combination of ellipsometry with other methods to study surfaces, such as Auger electron spectroscopy, ultraviolet and X-ray spectroscopy, electron diffraction and ion scattering methods.