Approximation of the absorption index of a film under the chromogenic effect

Using the Breit-Wigner distribution, a new approximate method of calculating the dispersion of the refractive index of a film that weakly absorbs in the visible wavelength range being stained due to the chromogenic effect after the deposition is proposed. We used an author’s analytical description for the transmittance of the sample and a method of calculating the dispersion of the optical constants from the experimental spectrum of transmission. The method is illustrated by the example of the electrochromic effect in WO$_{3-x}$ films.