Simultaneous phase control of Li_2 wave packets in two electronic states

摘要

State-selective phase control of rotational Li_2 wave packets, prepared simultaneously in the E(~1#SIGMA#_g~+) electronic state by one photon absorption and the A(~1#SIGMA#_u~+) electronic state by resonant impulsive stimulated Raman scattering, is demonstrated. Following the initial population of a rovibrational launch state on the A electronic potential energy curve with a cw laser, a single sub-picosecond wave packet preparation pulse centered near 800 nm simultaneously creates a two-state rotational wave packet in the E state (v_E=18, J_E=23 and 25) and a three-state rotational wave packet in the A state (v_A=15, J_A=22,24, and 26). A temporally delayed 800 nm probe pulse subsequently ionizes both electronic components of the wave packet to allow measurement of the time-dependent coherence in these two electronic states. Via phase manipulation of resonant transition frequencies contained within the preparation pulse, the phases of the E(18,25) and A(15,26) quantum states are either varied concurrently or individually controlled, whereas the phases of the other rovibronic states of the wave packet are in all cases held essentially constnat. This phase manipulation is shown to be more complex than a simple additive effect involving the phases applied to the resonant frequencies. These experimental results are compared with the prredictions of second order time-dependent perturbation theory. Although systematic discrepancies exist, most likely due to an additional phase introduced during the two-photon probe process, once these differences are accounted for, good agreement is found between experiment and perturbation theory.