Single-pulse phase-contrast nonlinear Raman spectroscopy.

High spectral resolution nonlinear vibrational spectroscopy with a single ultrashort pulse is demonstrated on a variety of samples. The spectral data are obtained by shaping the excitation pulse in order to control the relative phase between the weak resonant signal and the strong nonresonant background, in analogy with phase-contrast microscopy techniques. This is unlike the more conventional approach to nonlinear spectroscopy, in which the nonresonant background is reduced to a minimum. By measuring the spectrum of the coherent anti-Stokes Raman signal, it is possible to infer the vibrational energy levels in a band spanning almost an entire octave.