Transmittance and reflectance of a coated substrate with application to index measurement of thin films

Equations are derived for the transmittance and reflectance of a coated substrate of finite thickness. These equations are valid for thick substrates and thin films whose surfaces are specularly reflecting. It is found that the results are in good agreement with spectrophotometer readings of corresponding laboratory samples. Based upon the present results, a simple technique for calculating the refractive index of thin films from photometer readings is given.