Prolonged-excitation coherent Raman spectroscopy with spectral resolution beyond the transition linewidth using two tunable picosecond dye lasers

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Abstract
A time-resolved coherent anti-Stokes Raman technique is demonstrated that yields a spectral resolution beyond the linewidth obtained in spontaneous Raman spectroscopy. Two picosecond dye lasers, independently tunable with low timing jitter, are used. The coherent material excitation is generated by long pump pulses and monitored by short delayed probing pulses. Transiently narrowed Raman spectra are recorded by scanning the lasers over the resonances of interest and simultaneously monitoring the coherent scattering signal as a function of the excitation frequency. The technique is applied to molecular vibrations in liquids. The differences between the technique presented and standard coherent anti-Stokes Raman spectroscopy are demonstrated.