These days most modern ellipsometer system come with build in software for analysis for example the JY Horiba Ellipsometers that I use have modelling capabilities in the Delta Psi software. As you say optical properties you are interested in, you can use chose a suitable model that might describe the optical properties of the material, for example a Cauchy model for a thin film.

The programs that you use typically require a sample measurement of a substrate with and without the film as a reference.

If you don't have a system with such software you might find someone with something similar online, otherwise have a look at Ellipsometry and Polarized Light by Azzam and Bashara ISBN 978-0444870162 which describes how to program such things and is otherwise a very useful book for ellipsometry.

Psi is the amplitude ratio for s and p polarized light and is typically large when the reflectivity for p-polarized light is low. For a simple substrate this occurs at Brewster's angle. At the same time, the phase of the reflection coefficient changes 180 degree and is clearly visible in the measurement of Delta.

For thin films on a substrate the zero reflection coefficient for p-polarized light at Brewster's angle is no longer present and the peak in Psi with associated phase change in Delta disappears as the film gets thicker. As long as the film is thin compared to the wavelength Psi and Delta resemble that of a bare substrate. The change in the values of Psi reflects film thickness. I am not aware of working formulas for Psi and Delta in the limit of a single thin film on a substrate, but this should not be hard from the Azzam and Bashara textbook suggested by Jonathan Bramble.

For thicker films the phase change on propagation through the film becomes very significant and you get oscillations in both the r- and p-polarized reflectivity due to the interference of different contributions. These oscillations also enter in Psi and Delta, but It is much harder here to give an easy interpretation to Psi and Delta. For a single thin film on a substrate there are two Brewster angles that one can define where one of the reflections on the interfaces disappear. With this the oscillation due to interference effects in the film disappear as well. For that reason, these are interesting angles to include in your measurement.

If you simply want the optical properties or if you have more than a single film I would look for some software or the Azzam and Bashara textbook to get the optical properties by fitting Psi and Delta.

I have single zinc oxide grown on glass substrate, i want only optical properties

@ Chetan  I would like to know it too. Can you calculate the thickness from the raw data?