Evolution from quantum to classical fluctuation in low-frequency dynamics in liquids

Abstract We study the correlation between the onset time τs and the decay time τd of the exponential response by femtosecond optical Kerr effect (OKE) spectroscopy for various liquids and temperatures changing τd from ∼1 to ∼100 ps. From the results we investigate the random force fluctuation due to the microscopic motions that affects the macroscopic polarizability of the system. It is found that the nature of the polarizability fluctuation is, as a whole, non-Markovian, and gradually approaches to Markovian with increasing τd. Further the slowing down of the relaxational mode is related to the decreasing amplitude of the random force fluctuation.