I have transmittance of my thin film coated glass sample (Ts) with vacuum as reference. I also have transmittance of bare glass sample (Tref) with vaccum as reference. What will be the correct way to remove background from the spectra to get the extinction spectra of the thin film sample. I have two ways. Do (1-Ts/Tref)*100 or (1-Ts/1-Tref)*100. The first one is like relative transmitance and second one is like normarlisation of extinction spectra of the sample againts that of ref. The dark spectra was removed from the reference spectra so as to get 100% transmission before the measurement.
Neither! It does not make sense to try to "remove" the substrate. Instead you have to take it into account in a different way:
First, determine the optical constants of your substrate, then you have to do that for your film on the substrate. Why?
In a thin film you get interference effects which consist not only of an undulating baseline, but also of standing waves which lead to higher absorption due to the higher field intensity at the particular wavelength where they occur. You can get some more information here:
https://www.researchgate.net/project/Signal-enhancement-in-Transmission-and-Transflection-measurements-of-films
https://www.researchgate.net/project/Fast-and-reliable-Determination-of-the-true-Absorbance
Solutions are dispersion analysis or a Kramers-Kronig analysis. A hybrid solution (somewhat less complicated) has been published very recently:
Article Removing interference-based effects from the infrared transf...
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