Dear Zahra Mazaheri,

You have to use a model to fit the unknown parameters. Ideally you should measure the real thickness of your thin films using a surface profiler instrument.

Dear Zahra,

You can not estimate the n and k without using a model. Best way is use proper model to fit your psi and Delta. To calculate n and k, you don't need ellipsometer software, you can write a small code in matlab.

Dear Gaurav,

Thank you so much. I have to fit the experimental psi and delta with the calculated one through a nonlinear regression?

yes you got the point.