Autocorrelation Function from Power Spectral Density

It is possible to compute the autocorrelation function from the power spectral density of a light field with the help of the Wiener-Khintchine theorem. This autocorrelation function is directly related to the first-order correlation function and therefore the coherence time of the light. The function takes as the input the wavelenghts with corresponding power spectral density and computes the unnormalized first-order correlation function with the help of an inverse fourier transform.