Compositional control of rovibrational wave packets in the E(1Σg+) “shelf” state of Li2 via quantum-state-resolved intermediate state selection

Abstract

Compositional control in the preparation of rovibrational wave packets is demonstrated in the E(1Σg+) state of gas-phase Li2 molecules using ultrafast pump–probe laser spectroscopy combined with quantum-state-resolved intermediate state selection. The intermediate state, from which subsequent ultrafast excitation occurs, is a stationary rovibrational level in the A(1Σu+) state of Li2, produced by cw laser excitation from the ground X(1Σg+) state. The effect that the intermediate state has on the final composition of the wave packet is investigated by comparing the transients resulting from ultrafast pump–probe excitation of two different intermediate states (vA=14, JA=18 versus vA=13, JA=18). In these experiments the pump wavelength is compensated so that in each case the same E-state eigenstates (vE=13–18, JE=JA±1) make up the wave packet, but with different amplitudes. Theory predicts, and experiments confirm, that the relative amplitudes of the rovibrational eigenstates are strongly dependent upon the intermediate state and determine the spatial and temporal evolution of the wave packet. Evidence for this includes differences in the observed pump–probe transients and dramatically different amplitudes of the beat frequencies in the Fourier analysis of the time-domain transients. Theoretical three-dimensional wave packet simulations highlight how the composition of the wave packet is used to vary its spatial and temporal evolution.

Quantum dynamics simulation of the ultrafast photoionization of Li2

“…Thus the raw data consist of current as a function of delay time. Single-photon transitions are the most relevant for the interpretation of the signal, as shown experimentally [8][9][10][11] and confirmed theoretically in the following sections.…”

“…The X surface and the X→A excitation stage are not required in the present theoretical analysis, but have been described in detail previously. 9,10 The pump and probe sequence begins from the single rovibrational state on A. The femtosecond pulses simulated in this paper have the same energy spectrum and the same range of intensity as those in the experiments.…”

“…Quantum interference effects depend heavily on the coherence properties of both the molecular sample and the light source. Accurate ultrafast pump/probe experiments [8][9][10] have employed an initial state selection from which to launch the wave packet, greatly simplifying the wave packet prepared.…”

Recent advances in ultrafast-laser-based spectroscopy and imaging for reacting plasmas and flames

“…Molecular wavepacket dynamics and their control has been demonstrated employing fs lasers resonant to molecular transitions in various diatomic molecules employing pumpprobe configurations [256][257][258][259].…”

Femtosecond wave-packet dynamics in cesium dimers studied through controlled stimulated emission

“…[1]. Since then, the wave packet generation and evolution have been demonstrated and thoroughly studied for a number of diatomic molecules, including I 2 [2,3], Na 2 [4,5], Li 2 [6,7], and many others [8,9]. Besides these successful research works, the two-color, pumpprobe laser experiment has been performed in Refs.…”