Bulletin of the American Physical Society
38th Annual Meeting of the Division of Atomic, Molecular, and Optical Physics
Volume 52, Number 7
Tuesday–Saturday, June 5–9, 2007; Calgary, Alberta, Canada
Session N2: Molecules in Strong Optical Fields |
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Chair: A. Mullin, University of Maryland Room: TELUS Convention Centre Macleod C |
Friday, June 8, 2007 8:00AM - 8:36AM |
N2.00001: Photonic Reagents: Strong Field Laser Pulses for Controlling Chemical and Physical Processes Invited Speaker: This presentation will focus on the latest developments in the area of using strong-field laser pulses to manipulate chemical systems in both the gas and condensed phase. The laser intensities are sufficient to alter the electronic Hamiltonian of a molecule or condensed phase system. In fact, the perturbations are on the order of the electronic level spacing between the ground and electronic states of any molecular system. This implies that anticipated chemical reactivity will be at least on the order of that induced by conventional reagents and enzymes. Strong laser fields are capable of inducing massive electron polarization and we now demonstrate that proton migration is also possible on the timescale of the laser pulse. In combination with laser pulse shaping methods and computer-based feedback control, strong field chemistry has initiated a plethora of new laser-chemistry experiments. Recent experiments involving the use of strong field chemistry to provide a novel, rapid, and selective sensing scheme will be discussed, as will dimensionality reduction tools to predict and navigate the high dimensional search spaces. The use of adaptive feedback to control laser-induced filamentation in the solution phase will also be described. [Preview Abstract] |
Friday, June 8, 2007 8:36AM - 9:12AM |
N2.00002: Angle Dependent Ionization of Small Molecules Invited Speaker: The ionization probability and both the direct and re-scattered photoelectron momentum spectrum are all sensitive to the angle of a molecule with respect to the laser field. We experimentally measure the sensitivity of the ionization probability to molecular alignment using H$_{2}$ the simplest molecule as well as N$_{2}$, O$_{2}$, and CO$_{2}$. Concentrating on O$_{2}$ and N$_{2}$ we then demonstrate the natural quantum interference that occurs when the electron tunnels from perpendicularly aligned O$_{2}$, contrasting it with N$_{2}$. We show that the direct electrons preserve the symmetry of the orbital from which they tunnel, filtered through the momentum filter of the tunnel. Finally we show that the re-scattered electrons are also sensitive to molecular alignment, writing the molecular structure onto their angular distribution. [Preview Abstract] |
Friday, June 8, 2007 9:12AM - 9:48AM |
N2.00003: Controlling the rotational motion of asymmetric top molecules by laser pulses Invited Speaker: While the vast majority of previous studies on laser induced alignment of small molecules dealt with linear systems, interest is now shifting to asymmetric tops due to both the new physics involved and the broad range of applications. However, controlling the rotational motion of asymmetric tops represents, in general, a much harder task because they are characterized by three axes with different moments of inertia and different polarizability components. This talk will discuss recent studies on laser alignment of asymmetric tops. First, we show how the alignment dynamics induced by a single linearly polarized short laser pulse can be controlled by the fluence. When the fluence is increased the complex non-periodic revival structure of an asymmetric top approaches a simple periodic rotation around a single axis. Second, we introduce a new method for 3-dimensional (3D) alignment control by combining two linearly polarized pulses laser pulses, one short and one long compared to the molecular rotational periods. The long pulse strongly aligns the most polarizable molecular axis along its polarization axis while the orthogonally polarized short pulse sets the molecule in to controlled rotation about the axis aligned. As a result strong 3D alignment occurs immediately after the short pulse and is repeated periodically reflecting the revolution about the axis aligned. Our method opens new directions for field-free 3D alignment and for controlling internal rotations of molecules. [Preview Abstract] |
Friday, June 8, 2007 9:48AM - 10:24AM |
N2.00004: Non-perturbative Quantum Control via the Non-resonant Dynamic Stark Effect Invited Speaker: We will discuss Quantum control using the non-resonant Dynamic Stark Effect as a new and powerful tool. Dynamic Stark Control (DSC) applies to both molecular rotation and vibration. We show how DSC, which uses the electric field of the laser pulse, can be used to control electronic branching ratios in non-adiabatic photodissociation without any absorption of light [1]. We illustrate the use of this tool in creating molecular frame alignment, via our technique of `switched' wavepackets. We demonstrate full 3D, field-free, axis alignment of an asymmetric top rotor [2] -- literally `fixing the molecule in space' in order to make a measurement. \newline \newline [1] Science 314, 278 (2006). \newline [2] Phys.Rev.Lett. 97, 173001 (2006). [Preview Abstract] |
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