Control of photofragment angular distribution by laser phase variation

초록

When a molecule is dissociated through separate excitations by one or two polarized photons the fragment distribution is forward-backward symmetric with respect to the polarization axis. However,if the molecule is simultaneously excited by optical electric fields, E(ω) and E(2ω), the amplitude for excitation is a sum of an amplitude for absorbing one photon of frequency 2ω and an amplitude for absorbing two photons of frequency ω. When the sum is squared to obtain the fragment angular distribution, there is a cross product which depends on the phase difference Δφ= φ<inf>2ω</inf>-2φ<inf>ω</inf>. With suitable adjustment of the relative intensities at the two frequencies large unidirectionality can be obtained. The left-right anisotropy on the polarization axis depends on the symmetry of the transitions, real and virtual. In the most favorable case 97% of a particular fragment is ejected in one hemisphere and only 3% in the other. In a less favorable case 60% of the fragment is ejected in one hemisphere. © 1997 American Institute of Physics.