Abstract

By studying the dynamics of the laser excitation process in a dressed states picture, we have recently shown that, in many cases of photochemical interest, the time scale for molecular excitation is many orders of magnitude slower than the time scale for in tramolecular relaxation. As a result, single laser radiation offers little if any control over the form of the initial excitation in these cases. However, if one tunes two (or n) different lasers to two (or n) different molecular eigenstates, then a superimposition of the eigenstates will be prepared coherently. Furthermore, that coherent superimposition will continue to be the molecular state as long as the lasers are on. This coherent multicolor (CMC) excitation can be used to destructively interfere with the relaxed portions of the excited eigenstates. The result is excitation of a nonstationary molecular state which does not evolve in the presence of the laser field. The localization is locked in by the coherence of the multicolor excitation. We apply the CMC proposal to preparation of localized vibrational overtones of molecular local modes and to the separation and selective control of excitations of singlet and triplet vibronic states. Control of unimolecular reaction rates and branching ratios is proposed and illustrated.

© 1986 Optical Society of America