Optical theory applied to infrared spectroscopy

Optical theory has been reviewed from the view point of infrared spectroscopy. Among the techniques used to determine the complex refractive index of materials, Kramers-Kronig analysis is summarized. The optical effects which distort spectra are discussed, especially for thin films. Transverse optic-longitudinal optic (TO-LO) splitting plays an important role in measurements at oblique angles of incidence. Interference affects the spectra not only as interference fringes but also as a decrease in peak intensities. The exact spectral simulation is compared with the prediction under the classic thin-film approximation. Optical theory should be applied for exact, quantitative analysis and/or detailed interpretation of spectra for thin films.