Phase-retrieval problems in infrared-visible sum-frequency generation spectroscopy by the maximum-entropy method

Abstract

A phase-retrieval procedure based on the maximum-entropy method is applied to infrared-visible sum-frequency generation spectroscopy. Several typical effects on the error phase are also examined with the aid of a known theoretical model. The interference between the resonant and the nonresonant parts changes the behavior of the error phase. Even in some cases when the nonresonant part is complex, the error phase becomes like a step function. This result contradicts the smoothness assumption for the error phase, and the whole phase-retrieval procedure breaks down in these cases. A comparison of the results of phase-retrieval procedures between infrared-visible sum-frequency generation and coherent anti-Stokes Raman scattering spectra is made. Some ideas that worked well in previous analyses of coherent anti-Stokes Raman scattering spectra become inapplicable in the infrared-visible sum-frequency generation spectra in spite of the resemblance of their line shape functions. (C) 1997 Optical Society of America.