Ultrafast Spectroscopy of Non-Markovian Dynamics in a Dense Atomic Vapor

<p>This thesis presents results from ultrafast spectroscopy experiments and theoretical calculations of non-Markovian dynamics in a dense atomic vapor. For a dense atomic vapor the excitation pulses are short compared to the duration of collisions and the time between collisions is long compared to the collision duration. Thus there are distinct timescales that correspond to regimes in which the phase-coherence of the atomic superpositions is retained (called the non- Markovian regime) and regimes in which the phase memory is lost (called the Markovian regime). This is not the case for most condensed phase systems, in which the time between dephasing interactions, the interaction duration and the pulse width are of similar order. Using the current theory of stochastic fluctuations of the energy levels due to collisions, we simulate and fit the signatures of phase memory from two-pulse transient four-wave mixing experiments, providing support for the theoretical model that is commonly used for more complex condensed phase systems. Further three-pulse experiments in conjunction with a theoretical derivation of the correlation function of frequency fluctuations using molecular dynamics simulations in an exciton picture provide insight into resonant effects in dense atomic vapors. In addition, distinct signatures of local field effects are observed and compared with theory. The results presented in this thesis provide support for theoretical models employed in more complex systems, contribute insight into the fundamental physics of dense atomic vapors, and exhibit the benefits of ultrafast spectroscopic techniques through the clarity of signatures representing system response.</p>
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University of Colorado Boulder
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