Application to a Liquid Surface

The fourth-order coherent Raman spectrum of a liquid surface was observed by Fujiyoshi et al. [28]. The same authors later reported a spectrum with an improved signal-to-noise ratio and different angle of incidence [27]. A water solution of oxazine 170 dye was placed in air and irradiated with light pulses. The SH generation at the oxazine solution was extensively studied by Steinhurst and Owrutsky [24]. The pump and probe wavelength was tuned at 630 nm to be resonant with the one-photon electronic transition of the dye. The probability of the Raman transition to generate the vibrational coherence is enhanced by the resonance. The efficiency of SH generation is also enhanced. 

2-mm thick hexadecane layer was placed on the oxazine solution. The vibrational coherence at the hexadecane/solution interface was pump-probed in a similar manner [27]. The light pulses traveled in the hexadecane layer and experienced group velocity dispersion before arriving at the interface. This undesired dispersion 

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