Model-independent maximum-entropy method for the analysis of sum-frequency vibrational spectroscopy

We have developed and applied a maximum-entropy phase-retrieval procedure to analyze sum-frequency vibrational spectra from a CCl₄/octadecyl tricholosilane/silica interface and a hydrogen-terminated diamond C(lll) surface. Some a priori knowledge of a nonlinear optical spectrum was employed for determining the phase of nonlinear optical susceptibility, and therefore the requirement for experimental phase measurement can be avoided. The results agree well with those from the Lorentzian line-shape model and justify the applicability of the a priori constraints employed in our phase-retrieval procedure.