Adiabatic climbing of vibrational ladders using Raman transitions with chirped pump lasers: effect of higher electronic surfaces and control of the shapes of vibrational wave packets

Abstract

AbstractUsing numerical solutions of the time‐dependent Schrödinger equation for the H2 molecule in intense laser fields we calculate the vibrational excitation induced by the Raman chirped adiabatic process (RCAP). We show that adding several higher electronic surfaces to a simple two‐surface model improves the efficiency of the ladder‐climbing process at intensities below the adiabaticity threshold. Furthermore, we show that although using photon energies close to the one‐photon electronic transition frequency allows the use of lower pump and Stokes intensities, in general, this leads to more population transfer to the upper electronic surfaces accompanied by a loss of selectivity in the vibrational excitation on the ground‐state surface. By contrast, considerable dissociation yields can be achieved when higher energy photons are used. We also investigate the structure of time‐dependant vibrational wave packets prepared by RCAP. We find that at specific times the wave packet is very well localised at large inter‐nuclear separations at which ionisation occurs with a probability 3 orders of magnitude larger than at the equilibrium separation. Copyright © 2007 John Wiley & Sons, Ltd.