Relaxation rate distribution from frequency or time dependent data

A method for the inversion of experimental susceptibility spectra or relaxation functions in terms of a spectrum of relaxation times is proposed. The method uses the Boas-Widder formula for the inversion of the Laplace transform for real variables. The method is tested numerically on known spectra for the Cole-Cole, Cole-Davidsson and Kohlrausch-Williams-Watts models as well as for more complex spectra obtained from the mode-coupling theory, and in all cases the agreement is very good.