Performs the FFT thickness analysis and returns the obtained thickness.

Parameters:

n_spec:                number of the spectrum in the spectrum list

wn_min:        wavenumber minimum of the used spectral range

wn_max:        wavenumber maximum of the used spectral range

fft_np:                number of data points used to sample the spectral range

d_min:                expected thickness minimum

d_max:                expected thickness maximum

n:                refractive index of the layer

VisualBasic example: wcd.fft_thickness(1,650,7000,2048,5,50,2.0)