Laser-field-induced coherent molecular librations in liquid

The temperature evolution of rotational spectra is demonstrated for four-photon scattering in water in the interval 0.1–8 cm^?1 (3–240 THz). A detailed numerical simulation of the spectra is performed. The best agreement is reached using the frequencies of the rotational resonances of free molecules. It is demonstrated that the contribution of coherent librations into the measured signal increases proportionally to the decrease in the shear viscosity of water. The four-photon-scattering spectra of water corresponding to an increase in the temperature and dilution with H₂O₂ are compared.