Calculation of thin film thickness from complex refractive index

Hello,

I want to ask how can one calculate the thickness of a thin film (or each of the thin films in a stack of 3-4 thin films on one another) when

- complex refractive index of each thin film is known (n and k). This refractive index is obtained from a single wavelength ellipsometer and not a spectroscopic ellipsometer
- approximate spectral reflectance/transmission of each layer is known (measured with some spectrometers available in the market)

In short, I want to predit the physical thickness of a thin film based on n, k and spectral tendency

The spectral tendency is a general one and I know approximately where in the spectrum is the absorption band for each of these thin layers.

thank you very much for reply.

Regards,

Paritosh