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ANISOTROPY-INDUCED POLARIZATION EFFECTS IN DEGENERATE FOUR-WAVE MIXING SPECTROSCOPY: A NEW PROBE FOR MOLECULAR ORIENTATION AND ALIGNMENT

Please use this identifier to cite or link to this item: http://hdl.handle.net/1811/19006

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Title: ANISOTROPY-INDUCED POLARIZATION EFFECTS IN DEGENERATE FOUR-WAVE MIXING SPECTROSCOPY: A NEW PROBE FOR MOLECULAR ORIENTATION AND ALIGNMENT
Creators: Müller, Thomas; Wasserman, T. A. W.; Vaccaro, P. H.; Johnson, Bruce R.
Issue Date: 1998
Abstract: The influence of angular momentum (rotational) anisotropy on the nonlinear optical technique of Degenerate Four-Wave Mixing (DFWM) has been investigated theoretically by incorporating a state-multipole expansion for the zero-order density operator into a perturbative treatment for resonant matter-field interactions. The weak-field response evoked from a rovibronically-resolved DFWM process is found to be affected strongly by the presence of molecular orientation and/or alignment, thereby leading to the formation of ``anomalous'' polarization components in the emerging signal field that are absent in the case of rotationally isotropic samples. Experimental verification of this behavior was obtained through use of the doubly-resonant Stimulated Emission Pumping (SEP) scheme. In particular, polarized ultraviolet excitation of jet-cooled $CS_{2}$ molecules enabled the selective preparation of gas-phase ensembles having well-defined angular momentum anisotropy in an electronically-excited intermediate state [e.g., $V {^{1}}B_{2}(^{1} \Delta_{u})]$, as quantified by the distribution and correlation of probability amplitude among the magnetic sublevels comprising an isolated rovibronic line. Before the transient population/coherence created in this intermediate manifold could decay through radiative or nonradiative channels, polarization resolved DFWM spectroscopy was employed to probe transitions terminating on highly excited vibrational levels of the $\tilde{X} {^{1}} \Sigma^{+}_{g}$ ground electronic potential surface. Recorded data sets are in excellent agreement with theoretical predictions, thus suggesting an entirely new class of resonant four-wave mixing measurements designed to permit the extraction of spatial (angular momentum) information in a manner that is both background-free and insensitive to isotropic contributions.
URI: http://hdl.handle.net/1811/19006
Other Identifiers: 1998-TB-05
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