The role of microscopic and macroscopic coherence in laser control

In this article, we discuss microscopic and macroscopic coherences resultin g from multiple pulse excitation of molecular samples. The wave packet form alism is applied to describe the interference of wave packets within a sing le molecule (microscopic coherence) and the macroscopic interference betwee n the polarizations resulting from optical responses of a single molecule o r from different molecules (macroscopic coherence). Experimental virtual ec ho and stimulated photon echo measurements with noncollinear, degenerate fe mtosecond pulses are presented where both of these coherences are shown to control the observed dynamics. Theoretical simulations of the rovibronic dy namics observed experimentally on iodine vapor are presented. The role of t hese coherences in laser control of quantum dynamics is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.