Thickness and Refractive Index calculation from transmittance spectra Thin film

Refractive index and thickness of thin films are be calculated using swanepoel envelop technique from transmittance spectra of recorded with UV-Vis Nir Spectroscopy. we have calculated thickness and refractive using origin for envelop and excel for solving the equation.
for reference use swanepoel research paper of thickness and refractive index calculation from transmittance spectra of thin films.
Determination of the thickness and optical constants of amorphous silicon
R Swanepoel1