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Dynamic Phase and Population Control of State Selected Wave Packets in Li2

TitleDynamic Phase and Population Control of State Selected Wave Packets in Li2
Publication TypeThesis
Year of Publication2003
AuthorsBallard, JB

Pulse shaping of ultrafast pulses with a Liquid Crystal Spatial Light Modulator (SLM) is used to control both transient and non-transient state-resolved wave packet dynamics in Li2. In almost all of the experiments, a single launch state (generally A1Σu+ νA = 11, JA = 28) is prepared via excitation with a cw laser, from which a pump pulse excites a superposition of states on an excited electronic potential energy curve followed by a photoionizing ultrafast probe pulse. Using feedback and an Evolutionary Algorithm (EA), the weak field pump-probe photoionization signal at a single time delay is optimized in Li2 for the state E 1Σg+E = 9, JE = 27 & 29). First order time dependent perturbation theory is used to explain the mechanism by which the photoionization is maximized. Following this, the transient dynamics of excitation of wave packets is studied in detail. A clear separation is made between resonant and nonresonant effects. Both population and resultant phase in the molecule are transiently manipulated. By varying the polarization of the probe light, population dynamics can be separated from interfering wave packet dynamics, allowing precise determination of the instantaneous population and wave packet dynamics. A pulse shaping scheme is described that implements a sign inversion for one state of a two state superposition, and all sign inversion matrix elements are quantified. Elements of strong field coherent control are also explored in Li2. From the launch state, the strong optical field couples the A and E electronic states, inducing sequential ΔJ = ±1 transitions to populate states up to ΔJ = ±4. Taking advantage of Rapid Adiabatic Passage, state selectivity is controlled by manipulating chirp parameters on the excitation pulse, achieving selectivity of either Stokes or anti-Stokes quantum beats of nearly unity. Finally, wave packet dynamics on highly excited electronic states is examined. Electronic wave packets consisting of beating between bound states on the F1Σg+ and G1Πg electronic states are observed.

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