Abstract

The generation of coherent phonons and molecular vibrations using pulsed lasers has recently attracted much attention [1-8]. Systems for which such coherent transient modes have been studied include molecular crystals and dyes [1], semiconductors [2], semimetals [3], high-T_c superconductors [4-5] and ferroelectrics [6-7]. As with other stimulated processes, phonon coherences result from nonlinear coupling between photons and the vibrational field. While in most cases the relevant mechanism has been ascribed to stimulated Raman scattering, this has not always been supported by a symmetry analysis of its properties. In addition, there is some controversy surrounding experiments performed under resonant excitation [5,8].

© 1994 Optical Society of America