Coherent Transient Phenomena

Abstract

Three main processes determine the features of optical phenomena. The first is the dynamics of elementary radiators (atoms, molecules, excitons etc.) interacting with light. The second is the emission of light by elementary radiators. The third is the evolution of light waves within the medium under the influence of dispersion, diffraction, nonlinear compression and parametric wave interaction. Essential features of radiator dynamics and emission of light are brightly displayed in coherent optical transients such as free induction decay, optical nutation and various echo phenomena. The favourable condition of their formation is a resonant propagation of an ultrashort light pulses through such thin medium where dispersion and other processes inherent to wave propagation are inessential. In this case coherent transients exhibit the properties directly connected with medium structure. This circumstance is very attractive for spectroscopy especially for investigations of relaxation. The theoretical analysis of coherent transients becomes fairly simple for optically thin medium when the framework of a given field approximation in Maxwell-Bloch equations is valid. This approximation ignores the reaction of the medium to the passing light pulses. In spite of this simplicity coherent transients represent an important large class of nonlinear optical phenomena. This chapter is devoted to the description of the underlying main principles of coherent transients.