Comment on the inversion of Raman excitation profiles

The unique amplitude obtained by an inversion of an observed Raman excitation profile is one of minimal phase. As the frequency varies, the phase of such an amplitude can span a range larger than 2π. Therefore such an inversion can yield an amplitude that accurately reproduces the input profile. It is possible to add to the minimal phase additional terms but such modifications of the phase of the Raman amplitude cannot change the corresponding Raman excitation profile. Hence such terms cannot be determined from the profile and introducing them does not constitute an inversion procedure.