Bulletin of the American Physical Society
2006 37th Meeting of the Division of Atomic, Molecular and Optical Physics
Tuesday–Saturday, May 16–20, 2006; Knoxville, TN
Session A1: DAMOP Prize Session |
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Chair: Charles Clark, National Institute of Standards and Technology Room: Knoxville Convention Center Ballroom EFG |
Wednesday, May 17, 2006 8:00AM - 8:36AM |
A1.00001: Seeking ways to measure atomic dynamics in real time Invited Speaker: C.L. Cocke Although it is straightforward to visualize and calculate the time-dependent motion of atoms in molecules and electrons in atoms, making experimental movies of this motion is quite a different matter. I will discuss some momentum-imaging experiments which yield experimental information on the timing of rearrangements in light molecules. If the transient state of the system is initiated using a single collisional pulse, an intrinsic clock must be used. For example, the diffraction of electrons ejected from the K-shell of an atomic constituent of the molecule takes a ``picture'' of the molecule, and the correlation between the momentum vector of the photoelectron and the subsequent fragmentation pattern can be used to estimate the time scale for the latter process. If the transient state is created with a short laser pulse, an external clock (pump-probe) with a resolution of a few fs is possible. Even shorter times can be observed by using \textit{in situ} electron scattering from the molecular ion. Examples from double ionization of hydrogen and other light molecules by short laser pulses will be discussed. [Preview Abstract] |
Wednesday, May 17, 2006 8:36AM - 9:12AM |
A1.00002: Computational quantum field theory Invited Speaker: I will give an overview on recent attempts to solve the time-dependent Dirac equation for the electron-positron field operator. These numerical solutions permit a first temporally and spatially resolved insight into the mechanisms of how an electron-positron pair can be created from vacuum in a very strong force field. This approach has helped to illuminate a wide range of controversial questions. Some of these questions arise for complicated physical situations such as how an electron scatters off a supercritical potential barrier (Klein paradox). This requires the application of quantum field theory to study the combined effect of the pair-production due to the supercriticality of the potential together with the scattering at the barrier involving the Pauli-principle. Other phenomena include Schr\"{o}dinger's Zitterbewegung and the localization problem for a relativistic particle. This work has been supported by the NSF and Research Corporation. P. Krekora, K. Cooley, Q. Su and R. Grobe, Phys. Rev. Lett. 95, 070403 (2005). P. Krekora, Q. Su and R. Grobe, Phys. Rev. Lett. 93, 043004 (2004). P. Krekora, Q. Su and R. Grobe, Phys. Rev. Lett. 92, 040406 (2004). [Preview Abstract] |
Wednesday, May 17, 2006 9:12AM - 9:48AM |
A1.00003: Laser scattering in turbid media Invited Speaker: Light scattering in random media is an interesting research area from a fundamental and practical point of view. On the theoretical side, the precise relationship between the Maxwell, Boltzmann and diffusion descriptions are presently not very well understood. We have examined the validity of these three approaches based on numerical solution techniques. On the practical side, an improved understanding of this interaction has the potential to lead to new medical imaging devices based on lasers. We will report on our first experimental data and discuss how they can be modeled by Monte-Carlo simulations. Major portions of this research involved several undergraduate students who performed computer simulations and laboratory measurements. This work has been supported by funds from NSF and Research Corporation. S. Menon, Q. Su and R. Grobe, Phys. Rev. Lett. 94, 153904 (2005). S. Menon, Q. Su and R. Grobe, Opt. Lett. 30, 1542-1544 (2005). [Preview Abstract] |
Wednesday, May 17, 2006 9:48AM - 10:24AM |
A1.00004: Control and Measurement of Attosecond Pulses Invited Speaker: We introduce a new approach to attosecond measurement. We use a weak field to perturb the highly nonlinear generation process without significantly modifying it. Yet, the subtle changes that we can induce on the attosecond pulse can give us all information needed to measure the both the spatial and temporal properties of attosecond pulses. Our measurement relies on a phase ``gate.'' The phase of attosecond pulses is easily manipulated because attosecond pulses arise in an interferometric process --- the interferometer formed by an electron being removed by the atom, propagating in the laser field and re-colliding with the parent ion where the interference occurs. Slightly modifying (gating) the phase of the electron along the trajectory encodes spatial and temporal information. We also introduce a method for producing transient optical elements for attosecond pulses and high harmonics. For control we use a slightly stronger, yet still very weak control beam. We produce a diffraction grating in the nonlinear medium itself and we observe the diffracted radiation. These experiments are the high harmonic analogue to cross-phase modulation and 4-wave mixing. Gating is a general approach to measurement (and control), applicable to a broad range of dynamic measurements. Other gates are possible. Similar approaches can be extended to other areas of re-collision physics, opening the door to fully time resolved experiments in collision science and in nuclear physics. [Preview Abstract] |
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