I think this is a good start:Article Determination of refractive index and layer thickness of nm-...

There is quite some company info on ellipsometry by the manufacturing companies, e.g. the following three:

https://www.jawoollam.com/resources/ellipsometry-tutorial

https://www.horiba.com/gbr/scientific/technologies/spectroscopic-ellipsometry/spectroscopic-ellipsometry/

https://qd-uki.co.uk/wp-content/uploads/2019/07/Basic-Ellipsometry-Datasheet.pdf

I think the classical work in this field is the book by Azzam and Bashara,

"Ellipsometry and Polarized Light" should also be mentioned, but it is not

directly for beginners.

Further a comment. Be aware what you want to measure. For dielectrics

with a deep penetration depth of the light, the dielectric constant or its related refractive index is a good material parameter and it can be called a bulk parameter. If the penetration depth is less and the interest is also in

surface related phenomena, so events taking place in the few outermost monolayers at the surface, you enter a different world. Concepts like a dielectric constant are not well defined there anymore and theoretically that area is still problematic. This holds for the surface of semiconductors and even more for the surface of metals.