In this work the maximum
max
Tsam and the minimum
min
Tsam of the spectral
transmittance of weakly absorbing thin films deposited on non-absorbing substrate is
analyzed as a function of refractive indices of both substrate and film according to the
coherence condition. Also the ratio of Tsam. /Tw (where Tw is the transmittance of the
uncoated substrate) is obtained for both homogeneous and inhomogeneous films. The
results of the analysis enabled us to interpret the increment of the ratio (Tsam. / Tw)
over unity, distinguishing the inhomogeneous and homogenous films and obtaining the
refractive index of the film.