A FEMTOSECOND SNAPSHOT OF CRYSTALLINE ORDER IN MOLECULAR LIQUIDS

A theoretical model of ultrafast dynamics in the optical Kerr effect i n molecular liquids is developed. It assumes that for short times ther e exist dynamic quasicrystalline structures including a central molecu le and its nearest neighbors. The interaction of such structures with a femtosecond laser pulse leads to excitation of vibrational modes (lo cal phonons) which are responsible for subpicosecond nonlinear polariz ability of the liquid. The results of numerical calculations performed for benzene show a very good agreement with the experimental data. Th e lifetime of the dynamic quasicrystalline structures in benzene, at r oom temperature, is estimated to be about 200 fs. (C) 1998 American In stitute of Physics. [S0021-9606(98)50520-X]