Bulletin of the American Physical Society
46th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 60, Number 7
Monday–Friday, June 8–12, 2015; Columbus, Ohio
Session P4: Focus Session: Controlling Matter with Light |
Hide Abstracts |
Chair: Brett Esry, Kansas State University Room: Union DE |
Thursday, June 11, 2015 2:00PM - 2:30PM |
P4.00001: Supercontinuum Generation and Polarization as Probes of Laser Filamentation Dynamics Invited Speaker: Michael Chini In laser filamentation, the microscopic dynamics of ionization and dipole excitation result in macroscopic reshaping of the spatial, temporal and spectral properties of the propagating laser pulse. Therefore, the properties of the laser pulse after filamentation can provide a sensitive probe of the rich interaction dynamics which enable laser propagation as a filament. In this talk, I will present measurements of the supercontinuum spectrum and polarization state of the light emitted from a laser filament with elliptical input polarization. We observe anomalous spectral broadening and polarization rotation for particular values of the input laser ellipticity, which are present only for molecular gases. The results demonstrate the strong interplay between polarization and supercontinuum generation in filamentation, and call for accurate modeling of the nonlinear susceptibility and ionization of molecular gases. Furthermore, I will discuss the progress of current investigations into the dynamics of filamentation in the few-optical-cycle regime, enabled by the development of new high-energy and high-repetition rate laser sources based on Optical Parametric Chirped Pulse Amplification (OPCPA). [Preview Abstract] |
Thursday, June 11, 2015 2:30PM - 3:00PM |
P4.00002: Control and Manipulation of Matter using Intense Single-Cycle THz Pulses Invited Speaker: Robert Jones The availability of broad-band, single-cycle THz pulses with MV/cm peak fields affords new opportunities for controlling, manipulating, and probing matter. For example, we are using THz pulses to directly drive rotational transitions in molecules, creating and/or modifying, without ionization or electronic excitation, rotational wave packets which exhibit specific time-dependent behavior such as transient field-free orientation. In addition, at fields that are too weak to cause bulk surface damage or induce electronic excitation/ionization from tightly bound electronic states in atoms or molecules, we have shown that THz pulses can transfer substantial momentum and energy ($>$ 100 eV) to free electrons. Accordingly, they can serve as non-invasive time-resolved probes of electron emission or, potentially, modify laser-driven electron trajectories to influence electron re-scattering during HHG or other strong-field physics applications. We have also found that we can produce, without damage, high energy electrons (several keV) from metallic nano-tips exposed to intense THz pulses. The initial emission appears to be the result of Fowler-Nordheim tunneling in the enhanced THz field at a tip's surface. However, the dynamical mechanism responsible for the high electron energies appears to depend on the surface structure. [Preview Abstract] |
Thursday, June 11, 2015 3:00PM - 3:12PM |
P4.00003: Production of extremely high-lying states by 80-GHz microwave fields Alexandr Arakelyan, Thomas F. Gallagher It was previously reported that ionization of Rydberg atoms of Na and Li by strong microwave (MW) fields of 17 and 38 GHz yields a substantial fraction of population left in the high-lying states with n $>$ 250. This phenomenon was observed for any initial state at least fractionally ionized and was reported as a consequence of MW ionization of atoms. We present results of a similar experiment conducted with an 80-GHz MW field. The production of the high-lying states after the strong 80-GHz pulse is observed, but, in contrast to previous studies, not for any initial state. The high-lying states are only observed if atoms are excited to a zero-field state that is in a multiphoton resonance with the ionization limit (IL). We attribute the difference in the results of 80 and 17-GHz experiments to the fact that the ponderomotive shift is 4 and 90 GHz, respectively, at 100-V/cm. Consequently, we show that the high-lying states are produced if an initial state can be shifted in resonance with the IL. We also report MW ionization thresholds observed at 80 GHz to be much higher than those measured at 15 GHz: a transition to n+1 state occurs only when big static field is present. Moreover, unlike results of 15-GHz experiment, ionization thresholds depend strongly on the width of the MW pulse. [Preview Abstract] |
Thursday, June 11, 2015 3:12PM - 3:24PM |
P4.00004: Time Dependent Susceptibility of Helium Andrew Spott, Andreas Becker, Agnieszka Jaron-Becker Understanding the interaction of an atom with a laser field during exposure to the pulse is necessary for accurate time domain descriptions of the propagation of high intensity pulses used in processes such as filamentation. To this end, we have developed an ab-initio nonperturbative method to calculate and analyze the recently observed time-dependent susceptiblity of an atom during its interaction with a short intense laser pulse. Results for the time-dependent susceptibility of helium for different laser pulse intensities will be presented. [Preview Abstract] |
Thursday, June 11, 2015 3:24PM - 3:36PM |
P4.00005: Molecular stopwatches, cogwheels and ``spinflakes'': studying the dynamics of molecular superrotors Aleksey Korobenko, Alexander Milner, John Hepburn, Valery Milner Using the technique of an optical centrifuge, we excite diatomic molecules to ultrafast synchronous rotation. Femtosecond velocity-map imaging allows us to visualize and study the coherent dynamics of molecular superrotors under field free conditions and in external magnetic field. We demonstrate that when the created rotational wave packet is narrow, its free evolution is nondispersing and follows the motion of a classically rotating dumbbell or a hand of the smallest natural stopwatch. For wider rotational distributions, we observe the breakdown of classical rotation, when a dumbbell shape changes to that of a ``quantum cogwheel'' -- a molecular state simultaneously aligned along multiple direction. Our measurements in external magnetic field reveal other peculiar aspects of the rich dynamics of molecular superrotors. The rotation of a non-magnetic molecule interacts with the applied field only weakly, giving rise to slow precession of the molecular angular momentum around the field direction. In contrast, the electronic spin of a paramagnetic superrotor mediates this interaction, causing the initial disk-like angular distribution to split into several spatial components, each precessing with its own frequency determined by the spin projection. [Preview Abstract] |
Thursday, June 11, 2015 3:36PM - 3:48PM |
P4.00006: Dynamical Localization in Kicked Quantum Rotors Andrei Kamalov, Douglas Broege, Philip H. Bucksbaum The quantum periodically $\delta$-kicked rotor has been shown to experience localization within angular momentum space, rotational wavepacket amplification or annihilation, and Bloch oscillations, amongst other effects, depending on the choice of time-separation between individual kicks. Localization within rotation state space has been linked to Anderson localization within 1-D chains, and has been extensively studied with calculations. Previous experiments used cold atoms in optical lattices to measure a related localization phenomenon. We utilize a train of eight femtosecond scale pulses and compare the molecular alignment signal of a true quantum linear rotor at room temperature when it is kicked periodically and aperiodically. Our data is the first observation of the much studied dynamical localization phenomenon within the quantum rotor. [Preview Abstract] |
Thursday, June 11, 2015 3:48PM - 4:00PM |
P4.00007: Control of Spectral Interference Patterns in Broad Rabi Sidebands: Terahertz Quasi-Comb Structures Dmitri Romanov, Alex Filin, Robert Levis Coherent broadband radiation in the form of Rabi sidebands with an effective bandwidth $\sim$ 200 meV is generated in atmospheric-pressure gases in pump-probe experiments. The dynamic Rabi sidebands show characteristic fringe patterns of spatial-spectral interference, whose variable contrast is affected by decoherence processes. The spectrum envelope, the fringe contrast, and the fringe spacing variation in these patterns can be controlled by the intensity and shape of the probe pulse. We demonstrate such control experimentally and report analytic and numerical investigation of possibilities to produce a comb-like fringe structure. The sideband envelope is mainly determined by the sharpness of the driving probe pulse. The fringe contrast, defined by the maximum-to-minimum difference, depends strongly on the asymmetry of the driving pulse. The variation of inter-peak distance within a sideband was controlled using the temporal shape of the driving pulse. In a particular case of blue-shifted sideband emitted by excited oxygen atoms driven by a picosecond pulse of 800 nm carrier wavelength and $\sim$ 0.05 TW/ cm$^{2}$ intensity, a super-Gaussian pulse shape leads to almost equidistant fringes producing a comb-like spectrum over the interval from 1.60 to 1.66 eV. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700