Bulletin of the American Physical Society
43rd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 57, Number 5
Monday–Friday, June 4–8, 2012; Orange County, California
Session P7: Light-Matter Interactions and Structure |
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Chair: David Hall, Amherst College Room: Terrace |
Thursday, June 7, 2012 2:00PM - 2:12PM |
P7.00001: Absolute measurement of the nonlinear phase shift in the components of air Jared Wahlstrand, Yu-hsiang Cheng, Yu-hsin Chen, Howard Milchberg Filamentary propagation of ultrashort optical pulses in gases is generally agreed to arise from an interplay between self-focusing due to the optical Kerr effect and defocusing from electrons freed by ionization of atoms and molecules. However, despite intensive investigation for many years, the optical nonlinearity is still not understood with much quantitative accuracy. We present the results of supercontinuum spectral interferometry measurements on the components of air using a thin gas target. These experiments provide absolute measurements of the instantaneous and delayed rotational response, as well as a time-dependent phase shift due to ionization. We find no sign of a higher-order Kerr effect up to intensities near the ionization threshold. These measurements promise to bring a new level of precision to nonlinear optics at high intensity. [Preview Abstract] |
Thursday, June 7, 2012 2:12PM - 2:24PM |
P7.00002: Post-Ionization Medium Response to a Femtosecond Laser Pulse Dmitri A. Romanov, Robert J. Levis When an intense, femtosecond laser pulse ionizes an atmospheric-pressure gas, the optical response of the medium differs drastically from that of a regular weakly-ionized plasma. The initial charge distribution resulting from ionization is microscopically inhomogeneous, with the average electron density of 10$^{15}$-10$^{16}$ cm$^{-3}$. We considered the oscillations of virtually isolated and expanding electron clouds forced by the laser electric field. A simple analytical model predicts the amplitude of these forced oscillations as a function of time. This amplitude, as well as the related polarization of the medium, undergoes considerable enhancement when the system evolves through the transient resonance with the laser carrier frequency. The results impact the currently accepted picture of laser filamentation dynamics and call for modifications in existing theoretical models. [Preview Abstract] |
Thursday, June 7, 2012 2:24PM - 2:36PM |
P7.00003: Excitation of a single atom with a temporaly shaped light pulses Gleb Maslennikov, Syed Aljunid, Dao Hoang Lan, Kadir Durak, Victor Leong, Christian Kurtsiefer We investigate the interaction between a single atom and coherent optical pulses with a controlled temporal envelope. By switching the temporal shape from rising exponential to square profile, we show that the rising exponential envelope leads to higher excitation probability using lower photon number in a pulse. The atomic transition saturates for $\approx$ 100 photons in a pulse. Rabi oscillations with 100\,MHz frequency are visible in detected fluorescence for excitations powers of $\approx$ 1300 photons in a 15\,ns pulse. A possibility to excite the atom with pulses in a Fock states is discussed and the theoretical treatment is presented. \\[4pt] [1] Yimin Wang et al., Phys. Rev. A. {\bf 83} 063842 (2011)\\[0pt] [2] M. Stobinska et al., EPL {\bf 86} 14007 (2009)\\[0pt] [3] I. Gerhardt et al., Phys. Rev. A {\bf 79} 011402(R) (2009) [Preview Abstract] |
Thursday, June 7, 2012 2:36PM - 2:48PM |
P7.00004: Single-atom and multi-atom Excitation to Rydberg states Rui Han, Hui Khoon Ng, B.G. Englert We study two-photon Raman transitions between states $\vert $0$>$ and $\vert $1$>$ via an intermediate state $\vert $e$>$ that is far detuned so that it does not get significantly populated. This problem is often solved by adiabatic elimination in an interaction picture in which one then has an effective two-level Hamiltonian for states $\vert $1$>$ and $\vert $0$>$. However, there is more than one interaction picture and results may depend on which one is chosen (see E. Brion et al, J. Phys. A: Math. Theor. 40 1033 (2007), for example). In this talk, we present a full treatment of the single-atom Raman transition without adiabatic elimination. This serves as a benchmark for the choice of the correct interaction picture to use for adiabatic elimination for other situations. One of the very useful examples is the collective Rydberg excitation in a multi-atom system, where we discuss the correction in adjusting the detuning to compensate for the light shift compare to a single-atom system. [Preview Abstract] |
Thursday, June 7, 2012 2:48PM - 3:00PM |
P7.00005: Modeling A@C$_{60}$ atoms: diffuse versus square-well confining pseudo-potentials Jonathan King, Joshua Oglesby, Valeriy Dolmatov An empirical model approximating the C$_{60}$ cage potential by a square-well confining potential has played an important role in providing the initial understanding of photoionization spectra of A@C$_{60}$ endohedral atoms [1]. However, the square-well potential is discontinuous at its boarders. A more realistic confining potential must be diffuse, obviously. However, it is not at all clear \textit{apriori} to what degree replacement of a square-well potential by a diffuse potential may alter predictability of the model. In particular, should a large array of predicted data and phenomena made on the basis of a square-well potential model be re-studied with an eye on a more realistic diffuse potential boarders of C$_{60}$? It will be shown in this presentation, with H@C$_{60}$ and Xe@C$_{60}$ as case studies, that both the square-well and diffuse confining potentials lead to practically identical calculated data for A@C$_{60}$ photoionization spectra. Moreover, the latter are largely insensitive to the degree of diffuseness of the potential, in reasonable limits. Hence, either of said potentials is equally suitable for mimicking the C$_{60}$ cage.\\[4pt] [1] V. K. Dolmatov, Adv. Quant. Chem. \textbf{58}, 13 (2009). [Preview Abstract] |
Thursday, June 7, 2012 3:00PM - 3:12PM |
P7.00006: Creating and transporting Trojan wave packets S. Ye, B. Wyker, X. Zhang, F.B. Dunning, S. Yoshida, C.O. Reinhold, J. Burgd\"orfer The non-dispersive localized atomic states that have been most widely studied theoretically are termed Trojan wave packets because the mechanism responsible for suppressing dispersion (which is of classical origin) parallels that for stabilization of Jupiter's Trojan asteroids located near the L$_{4}$ and L$_{5}$ Lagrange points. In the present work non-dispersive localized Trojan wave packets with $n\sim $ 305 moving in near-circular orbits are created in the laboratory, and transported to localized near-circular Trojan states of higher $n$, $n\sim $ 600, by driving with a linearly-polarized sinusoidal electric field whose period is slowly increased. The protocol is remarkably efficient with over 80{\%} of the initial atoms being transferred to the higher $n$ states. The mechanisms involved in localization and transport are discussed with the aid of classical trajectory Monte Carlo simulations. [Preview Abstract] |
Thursday, June 7, 2012 3:12PM - 3:24PM |
P7.00007: Trojan wavepackets bound on Lagrange equllibrium points of two positive ions binary system in the strong magnetic field Matt Kalinski We once have shown that the combination of the Circularly Polarized Electromagnetic (CP) wave field and the central Coulomb proton field is capable to keep the hydrogen atom in the complex space-correlated coherent state of the electron in the rotating frame eliminating the principal time dependence [1]. This state corresponds to the stable and nondispersing electron wave packet moving around the circle in the laboratory frame. Here we show the existence of stable nondispersing single and two-electron wavepackets localized around Langrange equilibrium points of two positive ions in binary star configuration executing cyclotron motion around each other in strong eternal magnetic field. Unlike for the normal Trojan wavepackets they do not require external CP field to localize and correspond exactly to atom size scaled Trojan asteroids in the Sun-Jupiter system. The exact numerical simulations using Split Operator Fast Fourier Transform method are also provided for the single electron while the approximate time-dependent Hartree simulations for two electrons. \\[4pt] [1] I. Bialynicki-Birula, M. Kalinski, and J.H Eberly,``Lagrange Equilibrium Points in Celestial Mechanics and Nonspreading Wave Packets for Strongly Driven Rydberg Electrons,'' Phys. Rev. 73, 1777 (1994). [Preview Abstract] |
Thursday, June 7, 2012 3:24PM - 3:36PM |
P7.00008: Attosecond Lighthouse Effect: from tilted waves to isolated harmonic beams Jonathan Wheeler, Antonin Borot, Henri Vincenti, Sylvain Monchoce, Aurelien Ricci, Aurelie Jullien, Arnaud Malvache, Fabien Quere, Rodrigo Lopez-Martens Spatio-temporal coupling (STC) within a laser pulse is normally a negative feature to be avoided as it leads to non-uniform pulse characteristics and reduced intensity at focus. In this study, STC is purposefully introduced into the laser pulse leading to wavefront rotation at the focus. When such a modified focus is applied to plasma mirror harmonic generation, each harmonic pulse produced from cycle to cycle has a shifted propagation direction. Dependant on the degree of wavefront rotation introduced, this can lead from tilted harmonic spectra due to small displacements of the overlapping beams to fully isolated, individual pulses arising from each cycle of the driving laser pulse, the so-called Attosecond Lighthouse effect. This work discusses the recently measured results of spatially-separated, single harmonic beams from a solid target source obtained with 1kHz, CEP-locked, 800nm laser pulses of both 25 and 5 fs duration. [Preview Abstract] |
Thursday, June 7, 2012 3:36PM - 3:48PM |
P7.00009: Coherent Perfect Rotation: The conservative analogue of CPA Michael Crescimanno, Nathan Dawson, James Andrews The two classes of conservative, linear, optical rotary effects (optical activity and Faraday rotation) are distinguished by their behavior under time reversal. In analogy with coherent perfect absorption (CPA) resonances, where counter-propagating light fields are completely converted into other degrees of freedom, we show that in a linear conservative medium only time-odd (Faraday) rotation is capable of coherent perfect rotation, by which we mean the complete transfer of {\it any} arbitrarily oriented polarization of light into the other orthogonal polarization via the application of phased counter-propagating light fields. This contributes to the understanding of the importance of time reversal symmetry in perfect mode conversion that may be of use in optical device design. [Preview Abstract] |
Thursday, June 7, 2012 3:48PM - 4:00PM |
P7.00010: Discrete Energy Spectrum of a Classical Harmonic Oscillator in Classical Electromagnetic Zero-Point Radiation Wayne Huang, Herman Batelaan Since the early development of Quantum Mechanics, the discrete energy spectrum of atoms have been considered as the defining feature of Quantum Mechanics. However, when classical electromagnetic zero-point radiation is introduced as a modification of Classical Mechanics, our simulation shows that a classical harmonic oscillator can also exhibit a discrete energy absorption spectrum when excited by a laser pulse. This finding may be surprising given the use of a full classical theory, and it may help us identify fully quantum mechanical features in physical systems such as harmonic oscillator and ultimately atoms. [Preview Abstract] |
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