FFT analysis of a spectrometer signal

Hi all,

I am acquiring spectrometer (Ocean optics hardware) signal via USB data acquisition into LabVIEW.

The signal is

Wavelength(nm)        Intensity

xyz                              xyz

xyz                              xyz

xyz                              xyz

xyz                              xyz

The set up is as follows. The light is incedent on the PET film which has a thin coating of dielectric material using Ocean optics spectrometer.

Now i need to analyse this signal to find the thickness of the dielectric material and frequency components using FFT.

Excuse me if i am not clear about anything.