総説

電子増強ラマン散乱分光法の開発

由井宏治・澤田嗣郎

　Anomalous enhancement of the stimulated Raman scattering (SRS) of water molecules was observed when laser-induced plasma was generated by focusing a nanosecond pulsed beam into liquid water. Time-resolved spectroscopic measurements revealed that the SRS was emitted transiently before a phase transition from liquid to plasma and had the duration of several tens of picoseconds. A large amount of electrons, which were generated by avalanche photo-ionization within a few picoseconds by laser-irradiation, were suggested to play an important role in the vast enhancement of a Raman cross section of surrounding water molecules through changing their polarizability. The enhancement phenomenon was applied to spectroscopic analyses of the local hydrogen-bonding network structures of water in heterogeneous and/or restricted environments, such as a water-ethanol binary solution system and an air/water interface.