Calculation of Optical Constants of Thin Films Regarding Their Infrared Transmission and Reflection Spectra.

A general method of calculation of the transmittance and reflectance of thin films and thin film systems is described. The relations for a single thin film in general and for the most frequent special cases are given. Approximation methods for the determination of the optical constants of film materials are given taking account of the measured transmittance and reflectance values. For the case of a sample whose thickness is far greater than a wavelength, the relation of middle reflection which belongs to any angle of incidence is derived. A calculation program is presented for the determination of the optical constants of a ″thick″ sample from the transmission measured at a 90 degree incidence and from the reflection measured at any angle of incidence. The program is tested with measurement data obtained on germanium disks.