Dear Ahmed Saeed Hassanien, for answering to your question I need more details about your samples. For example, are they in thin film or bulk form. Are they transparent or absorbing. What about roughness and scattering etc.
Have in mind that the mentioned equation is for transmitted intensity on the boundary between two media with refractive indices of unit and n. It is not appropraite even in the simplest case of non absorbing plate.
Dear Ahmed Saeed Hassanien, as I mentioned the equation is not appropriate for thin films. There are few discussions in research gate about thickness and optical constants determination. You can check them if you are interested in. How thick are your films? What type is the substrate? What is the spectral range of interest. Are you able to measure reflectance as well?
Great thanks for your second reply , I am glad to inform you that if my samples are thick films of thicknesses more than .400 nm, the substrate is glass and in the same time I have only transmission measurements,