I think it would be easy to use a software package, such as Regress Pro ( http://franko.github.io/regress-pro/), rather than starting from scratch. See the following question.

https://www.researchgate.net/post/Ellipsometer_open_software

Be sure to check out the documentation and sample data. I wish you well on your ellipsometric investigations.

Ali Reza Jahangiri Thanks a lot! That is helpful!

Be aware that pedot:pss film is likely to be anisotropic, uniaxial, optical axis vertical generally. Ordinary index might have a drude contribution due to conductive properties whereas extraordinary index could fit simply with a cauchy like formula above 300 nm.

Michel Stchakovsky Thanks a lot, Michael!

Will be Drude-Lorentz optical model the suitable one at 380-1000 nm range? I've found in literature that the model is applicable when analysing PEDOT:PSS (DOI: 10.12693/APhysPolA.130.1242) and is the simplest one for such a material but there are few other sources that report applying simply Lorentz oscillators ( DOI: 10.1016/j.synthmet.2017.04.006) or Tauc-Lorentz model (ISBN 978-3-642-33956-1) and that is very confusing :(

Thanks forward! :)

anisotropic materials will need at least two indices. In the pedot case, ordinary index will need drude-lorentz and extraordinary can work with simply lorentz or tauc-lorentz. I guess you should understand first the use of these 3 dispersions on isotropic materials such as for example, ITO for drude-lorentz and SiN for the 2 others.

Michel Stchakovsky Thanks a lot! Now things became much more clear :)))

I am currently working on this material. I would be happy if we could share some information on how to do the ellipsometry analysis.

Nahid Ahmadian I've got help from the expert Petr Janicek Feel free to coordinate in case if it is still needed