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 S2: Nanoplasmas and Ponderomotive Potentials |
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Chair: Robert Jones, University of Virginia Room: Imperial Center |
Friday, May 28, 2010 2:00PM - 2:30PM |
S2.00001: Acceleration of neutral atoms in strong short-pulse laser fields Invited Speaker: Kinematic manipulation of neutral atoms in inhomogeneous laser fields has been widely studied for weak to moderately strong laser fields. Here we report on experiments where we have investigated kinematic effects on neutral atoms using strong short-pulse laser fields with intensities up to 10$^{16}$ Wcm$^{-2}$ and pulse durations in the range from 40 to 120 fs. We measure deflections of neutral atoms, which correspond to ultra strong accelerations with magnitudes as high as 10$^{14}$ times Earth's gravitational acceleration. This is - to the best of our knowledge - by far the strongest acceleration of neutral species in external fields. The momentum transfer to the neutral atoms during the short interaction time is by far stronger than what one would expect from the dipole force acting on the ground state atoms. To explain our findings we first state that it is of vital importance for our investigations that atoms can survive strong laser pulses in long lived excited states. A quantitative model for the underlying excitation mechanism is based on an extension of the three step model of strong field atomic dynamics. In essence, it is a ``frustrated tunnel ionization (FTI)'' process, where the tunnel electron is oscillating strongly in the laser field but eventually recaptured into an excited state of the neutral atom after the laser pulse is over. The observed deflection of the neutral atoms can be attributed to the ponderomotive force that is acting on the quasi free electron during the laser pulse, in accord with the FTI mechanism. It converts quiver energy of the electron partially into centre-of-mass motion of the whole atom, since the ionic core and the tunnel electron are coupled by the Coulomb force. Observed deflections for He and Ne atoms for different laser parameters are in very good agreement with our theoretical predictions. Implications of our results for strong field physics and further prospects will be discussed. [Preview Abstract] |
Friday, May 28, 2010 2:30PM - 3:00PM |
S2.00002: High harmonics and attosecond pulses emerging from laser filament Invited Speaker: We have performed fully non-adiabatic calculations of filamentation self-compression and the generation of coherent XUV radiation via harmonic generation in argon at atmospheric pressure. We show that both the high-intensity laser pulse and the XUV radiation can be coupled out of the filament via a short pressure gradient, and that the XUV light emerges from the truncated filament as an isolated self-focused attosecond pulse with a peak intensity approaching $10^{11}$~W/cm$^2$. We show that the laser intensity in an ultrashort pulse filament can exceed the clamping intensity by more than a factor of three over several cm of propagation, and discuss that the XUV yield presents an excellent diagnostic of these intensity spikes because of its extremely nonlinear dependence on peak intensity. [Preview Abstract] |
Friday, May 28, 2010 3:00PM - 3:30PM |
S2.00003: High Intensity Femtosecond XUV and X-ray Pulse Interactions with Atomic Clusters Invited Speaker: While the dynamics of clusters exploding under the irradiation of intense near IR pulses has been well studied over the past ten years, dynamics of clusters subject to intense, femtosecond short wavelength pulses have only recently come under study. Initial results show some similarities with cluster dynamics observed in IR pulses, such as high charge state production and fast ion ejection from the exploding clusters. However, the mechanisms for these phenomena appear to be somewhat different in the short wavelength pulses. In this talk, I will present results on explosions of argon, xenon and methane clusters irradiated by XUV pulses produced by high harmonic generation at wavelengths near 30 nm and by femtosecond x-ray pulses produced by the Linac Coherent Light Source (LCLS). I will discuss the mechanisms for high charge state production and examine the effects of plasma continuum lowering on photo-ionization of the cluster atoms. I will also consider the nature of the cluster explosions comparing our results in the XUV and X-ray region with our previous results on clusters exploding in intense 800 nm pulses. [Preview Abstract] |
Friday, May 28, 2010 3:30PM - 4:00PM |
S2.00004: Relativistic Attosecond Electron Bunches from Laser-Illuminated Droplets Invited Speaker: The generation of relativistic attosecond electron bunches is observed in three-dimensional, relativistic particle-in-cell simulations of the interaction of intense laser light with droplets. The electron bunches are emitted under certain angles which depend on the ratios of droplet radius to wavelength and plasma frequency to laser frequency. The mechanism behind the multi-MeV attosecond electron bunch generation is investigated using Mie theory. It is shown that the angular distribution and the high electron energies are due to a parameter-sensitive, time-dependent local field enhancement at the droplet surface. [Preview Abstract] |
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