Coherent Picosecond Interactions

Abstract

The advent of a coherent light source, the laser, marks the beginning of coherent experiments in the optical part of the electromagnetic spectrum. Numerous coherent phenomena have been elucidated in recent years, some of which are discussed in various chapters of this volume. Most of these experiments were performed with metal vapors or molecular gases at low pressure where the dephasing times are long, of the order of 10^-9 s or more. In these cases, commercial electronic detection systems may be used even for the study of transient processes. In the condensed phases at room temperature fast interactions occur between the closely packed molecules. It is not surprising that coherently excited systems lose the phase relation quite rapidly at 300 K. In fact, new experimental methods working in the time domain of picoseconds (10^-12 s) were required to observe directly the vibrational dephasing time T₂ of molecules in liquids and solids.