Abstract

We have developed a new and general molecular dynamics formalism which simulates the time-evolution of the interactions of an intense laser field with an ensemble of molecules in a liquid or dense gas, at time-scales up to a few picoseconds. Pertubation theory and molecular orbital theory are used to obtain individual molecular polarizabilities, and then the molecular dynamics simulation generates the macroscopic nonlinear susceptibilities (χ⁽ⁿ⁾) which incorporate local field effects. Apply the intense laser field and we then obtain the field-induced dipoles and observe the ordering of the liquid structure which arises from the new intermolecular forces and the local torques evaluated in time steps ranging from 10 to 100 fs. Relaxation and randomization is achieved by collisional interactions. The magnitude and direction of the induced electronic dipole moment is evaluated and the orientational pair correlations calculated from which the time-dependent molecular contribution to χ⁽³⁾ is determined. Molecular parameters are used to link all these results to the experimental observations in ultrafast laser spectroscopy of optical Kerr transients and four wave mixing studies of molecular motion in liquids and binary systems.

© 1984 Optical Society of America