Bulletin of the American Physical Society
41st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 55, Number 5
Tuesday–Saturday, May 25–29, 2010; Houston, Texas
Session C3: Focus Session: Strong Field Coherent Control |
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Chair: George Gibson, University of Connecticut Room: Imperial West |
Wednesday, May 26, 2010 2:00PM - 2:12PM |
C3.00001: Dynamic Broadband Rabi Shifting in Laser-Generated Micro-Plasmas Ryan Compton, Alex Filin, Dmitri A. Romanov, Robert J. Levis Coherent broadband radiation in the form of Rabi sidebands is observed when a picosecond probe laser propagates through a weakly-ionized, electronically-excited micro-plasma generated in the focus of an intense pump beam. The sidebands arise from the interaction of the probe beam with pairs of excited states of a constituent neutral atom via the induced Rabi oscillation. The pertinent excited states with dipole transitions near the laser carrier frequency become populated in the process of plasma cooling evolution (oxygen and argon plasmas were studied). Sideband shifting of $>$ 90 meV from the carrier frequency results in an effective bandwidth of 200 meV. The sidebands are controlled by the intensity and shape of the probe pulse; with amplitude, shift, and spectral fringes in agreement with the predictions of a time-dependent generalized Rabi-cycling model. Thus, the giant Rabi shift is both tunable and coherent over a wide range of frequencies and over a wide range of atomic transitions. [Preview Abstract] |
Wednesday, May 26, 2010 2:12PM - 2:24PM |
C3.00002: Velocity map imaging as a tool for recovering mechanistic information from adaptive strong-field coherent control E. Wells, R. Averin, B. Jochim, J. McKenna, S. De, D. Ray, M. Zohrabi, K.D. Carnes, M.F. Kling, I. Ben-Itzhak Adaptive control schemes which couple experimental feedback to a genetic algorithm to identify an optimally-shaped ultrafast laser pulse have become popular, but often it is difficult to recover information about the control mechanism. As we demonstrate with CO, the incorporation of velocity map imaging into the control loop allows simultaneous optimization of the dissociation angle and fragmentation branching ratio. Moreover, the kinetic energy release information obtained from the image produced by the optimal pulse, when combined with knowledge of the ionic potential energy curves, yields clues about the dissociation mechanism. [Preview Abstract] |
Wednesday, May 26, 2010 2:24PM - 2:36PM |
C3.00003: Deciphering optimal control fields Guan-Yeu Chen, Wendell T. Hill, III Pulse shaping coupled with adaptive feedback (genetic algorithm, GA) provides an experimental knob to control dynamics not readily available by other means. The optimal fields, however, are generally unintelligible. To address this problem, we chose to control a well-defined mode - bending - in a relatively simple triatomic system, CO$_2$ with a strong field. We have shown that the control pulse can be deciphered by comparing GA searches performed with radically different parameter sets. Specifically we first controlled the bending by running a GA search with a reduced parameter set, restricting the solutions to features that were straightforward to associate with the dynamics. We then repeated the search with an unrestricted parameter set and compared the two solutions. Both searches showed enhancement and the similarities were remarkable and enabled us to identify the dynamics responsible for the control. These results will be discussed in term of general applicability to strong-field adaptive control. [Preview Abstract] |
Wednesday, May 26, 2010 2:36PM - 2:48PM |
C3.00004: Formation and Dissociation of Transient Molecular States with Ultrafast X Rays James Glownia, James Cryan, Philip Bucksbaum, Ryan Coffee We report the first pump-probe spectra using 1 keV pulses from LCLS to excite N$_2$ in delayed coincidence with 800 nm laser pulses. The relative timing between the pump and probe was controlled to within 100 femtoseconds. We determined the timing based on the rapid formation of nitrogen dications by x-ray core ionization and subsequent Auger relaxation into a quasi-bound final state. Our operating photon energy primarily photoionized $K$-shell electrons. $KLL$ Auger relaxation rapidly follows, frequently leaving the molecule in one of several quasi-bound dicationic states. We subsequently triggered dissociation of these quasi-bound states by dressing the dications in the optical laser field, thus bond-softening the potentials into dissociation. [Preview Abstract] |
Wednesday, May 26, 2010 2:48PM - 3:00PM |
C3.00005: Time and frequency resolved detection of quantum coherences in systems, driven by strong ultrashort laser fields Stanislav Konorov, John Hepburn, Valery Milner Laser-induced coherences between the quantum states of atoms and molecules are the main ingredient in many optical processes, such as stimulated Raman or coherent anti-Stokes Raman scattering. In the regime of weak-field interaction in which the states are not modified by the applied fields, the coherences are simply defined by the resonant frequency components of the excitation field and can be easily controlled. With the increasing strength of atom-photon coupling, the quantum states are dressed by the driving field, resulting in strong dependence of the induced coherences on time, frequency and field amplitude. This complicates the ability to follow and control the coherent response of a system in the strong-field regime. We experimentally study the effects of the strong field on atomic coherence using four-wave mixing of high-power ultrashort laser pulses in the gas of Rubidium atoms. Utilizing the technique of frequency resolved optical gating, we detect both the amplitude and phase of the induced atomic coherence. This enables us to reconstruct the coherent response with high time and frequency resolution, understanding its complex dynamics and its dependence on the parameters of the driving fields. [Preview Abstract] |
Wednesday, May 26, 2010 3:00PM - 3:30PM |
C3.00006: Exploration and Control of Molecular Dissociation in Strong Asymmetric Laser Fields Invited Speaker: Intense lasers can be effective tools for manipulating and probing coherent dynamics within atoms and molecules. Asymmetric laser fields, in which there is a pronounced, controllable difference in the peak amplitude in one direction over another, are particularly interesting in this regard. Such fields can be produced through carrier-envelope-phase stabilization of few-cycle laser pulses or by coherently combining even and odd harmonics of a laser pulse (e.g. with frequencies $\omega$ and 2$\omega)$. We have used such fields to explore asymmetric dissociation of multiply-charged homo- and hetero-nuclear diatomic and triatomic molecules. Robust high-contrast control over the emission direction of specific ion fragments is observed for target species with a variety of different molecular structures, suggesting a common dynamical mechanism. The phase, intensity, and pulse-duration dependence of the directional emission could provide new insight into the combined nuclear and electronic evolution, from the initial ionization step through expansion and subsequent ionization. [Preview Abstract] |
Wednesday, May 26, 2010 3:30PM - 4:00PM |
C3.00007: Exploring Quantum Control Landscapes with Gun and Camera Invited Speaker: Seeking effective controls over quantum phenomena entails a search over the control landscape. The landscape is defined as the observable objective as a function of the control, typically a shaped laser pulse. The topology and features of the quantum control landscapes greatly influences the quality of the achieved control and the efficiency of finding effective controls over quantum phenomena. Although the nature of an optimal control is highly system specific, surprisingly the landscape topology is generic for all quantum systems satisfying some basic assumptions. The background leading to the analysis of quantum control landscapes will be discussed, including relevant experimental and theoretical research. The broader physical consequences of these findings will also be considered. [Preview Abstract] |
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