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

Author
Abstract
<p>Pulse shaping of ultrafast pulses with a Liquid Crystal Spatial Light Modulator (SLM) is used to <span class="b">control</span> both transient and non-transient <span class="b">state</span>-resolved <span class="c">wave</span> packet dynamics in Li<sub>2</sub>. In almost all of the experiments, a single launch <span class="b">state</span> (generally A<sup>1</sup>Σ<sub>u</sub><sup>+</sup> ν<sub>A</sub> = 11, J<sub>A</sub> = 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 Li<sub>2</sub> for the <span class="b">state</span> <em>E</em> <sup>1</sup>Σ<sub>g</sub><sup>+</sup> (ν<sub>E</sub> = 9, <em>J<sub>E</sub></em> = 27 \&amp; 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 <span class="c">wave</span> <span class="e">packets</span> is studied in detail. A clear separation is made between resonant and nonresonant effects. Both <span class="g">population</span> and resultant <span class="f">phase</span> in the molecule are transiently manipulated. By varying the polarization of the probe light, <span class="g">population</span> dynamics can be separated from interfering <span class="c">wave</span> packet dynamics, allowing precise determination of the instantaneous <span class="g">population</span> and <span class="c">wave</span> packet dynamics. A pulse shaping scheme is described that implements a sign inversion for one <span class="b">state</span> of a two <span class="b">state</span> superposition, and all sign inversion matrix elements are quantified. Elements of strong field coherent <span class="b">control</span> are also explored in <span class="d">Li<sub>2</sub></span>. From the launch <span class="b">state</span>, the strong optical field couples the A and E electronic states, inducing sequential ΔJ = \textpm1 transitions to populate states up to ΔJ = \textpm4. Taking advantage of Rapid Adiabatic Passage, <span class="b">state</span> 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, <span class="c">wave</span> packet dynamics on highly excited electronic states is examined. Electronic <span class="c">wave</span> <span class="e">packets</span> consisting of beating between bound states on the F<sup>1</sup>Σ<sub>g</sub><sup>+</sup> and G<sup>1</sup>Π<sub>g</sub> electronic states are observed.</p>
Year of Publication
2003
University
University of Colorado Boulder
Advisors - JILA Fellows
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