You may try to use:
http://upload.wikimedia.org/math/0/e/8/0e89562d682f0e676039c5defe65ee3e.png
Mikail, if the terms have the usual meaning, you have given me the reflection coefficients formula. I am taking of the refravtive index
Dear P. Arun, maybe you should provide some more information.
1) how can you get the transmission data of the film through the substrate? Is the substrate transparent? If yes, did you measure the absorption of the sole substrate?
2) Are you working in normal or grazing geometry?
3) Are you measuring in X-rays, UV, or visible light?
4) do you have the film thickness in hand? Is it constant or variable from point to point?
Dear Daniele, The substrate is glass (transparent) for the visible spectra where light is falling normal to film. The thickness of the film can be measured by a profilometer.
I was trying to get information using the transmission data from a UV-visible spectrometer. Somehow, I am not comfortable with ellipsometry resutls
Ok, so you probably can exclude interferential effects in the substrate. I would proceed in this way:
1) measure the transmissivity of the substrate alone (e.g., in a point where the coating is not present. There must be some, since you use a profilometer to determine the film thickness, presumably a step measure)
2) measure the transmissivity of the substrate+coating
3) divide the result of 2) by 1) and derive the transmittance of the sole coating, as a function of the wavelength.
4) Now you can fit your transmissivity curve - which is likely to exhibit a quasi periodic trend with one of the programs available in the web (like IMD). However, for a quick estimation of the refractive index, you can simply measure the period (\Delta\lambda) of the interference pattern and find the average refractive index n between \lambda and \Delta\lambda from the formula 2dn = \Delta\lambda where d is the film thickness.
Hope this helps.
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