Picosecond Laser Spectroscopy and Molecular Dynamics: I Pump-Probe Spectroscopy Techniques and Photodynamics II Nonlinear Laser Spectroscopy and Molecular Motion

Abstract

The exciting and rapid developments of recent years in the generation and measurement of ultrashort pulses (1– 3) with pulse durations now as short as 30 femtoseconds (30 x 10–15s (4)), are driving the exploration of new physics and chemistry in condensed media in systems as diverse as semiconductors and cytochrome C. One vast and significant area in which the fundamental questions seem well characterised, but their resolution less so, is that of molecular dynamics in liquids. Not only is the microscopic description of the molecular structure and dynamics of liquids one of “the last frontiers”, to quote Dr. Yarwood’s opening remarks, it is also one of the new frontiers for ultrafast spectroscopy, if one views the research potential from an interdisciplinary perspective (5). Direct access to the picosecond (ps) and now femtosecond (fs) time domain is a reality that hopefully over the next five years will permit direct, time-ordered optical observations of the dynamical interactions that accompany any molecular motion in a liquid, as the system is perturbed (far) from and returns to equilibrium. Because of the separation of timescales which underlies some events, it will be possible to explore dynamical interactions in the time domain that appear simultaneously in the wings of the frequency domain, spectral scattering data.