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 C4: Attosecond Physics |
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Chair: Michael Chini, University of Central Florida Room: Union DE |
(Author Not Attending)
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C4.00001: Circularly polarized attosecond pulses for molecular atto-magnetism Andre D. Bandrauk Circularly polarized molecular high order harmonic generation, MHOHG, is modelled from numerical solutions of the time-dependent Schroedinger equation, TDSE, for the one-electron H2$+$ in the nonlinear nonperturbative regime of laser-molecule interaction. It is shown that molecules due to their nonspherical symmetry are the preferred medium for producing circularly polarized harmonics by few cycle intense IR(800,400nm) circularly polarized laser pulses. An intense TeraHz (4$\mu$m) pulse is combined to force recollision of the ionized electron with the parent ion thus enhancing the efficiency of the circularly polarized MHOHG process through single recollision [1]. Superposition of these harmonics allows for the synthesis of single circularly polarized attosecond (10$^{-18}$s) pulses. Such new ultrashort pulses allow for controlling electrons on their natural time scale [2].In particular the TDSE simulations illustrate the generation with such new pulses coherent quantum electronic currents inside molecules for the creation of attosecond magnetic field pulses of intensity $>$ 10 Teslas [3].\\[4pt] [1] KJ Yuan, AD Bandrauk, Phys Rev Lett 110,023003(2013)\\[0pt] [2] KJ Yuan, AD Bandrauk, Chem Phys Lett 592,334(2014)\\[0pt] [3] KJ Yuan, AD Bandrauk, Phys Rev A 88,013417(2013) [Preview Abstract] |
Tuesday, June 9, 2015 2:12PM - 2:24PM |
C4.00002: Time Delays in Two-Photon Ionization Andreas Becker, Jing Su, Hongcheng Ni, Agnieszka Jaron-Becker We present results of ab-initio numerical simulations of time delays in two-photon ionization of the helium atom using the attosecond streaking technique [1]. The temporal shifts in the streaking traces consist of two contributions, namely, a time delay acquired during the absorption of the two photons from the extreme-ultraviolet field and a time delay accumulated by the photoelectron after photoabsorption [2,3]. In the case of a nonresonant transition, the absorption of the two photons is found to occur without time delay. In contrast, for a resonant transition a substantial absorption time delay is found, which scales linearly with the duration of the ionizing pulse. The latter can be related to the phase acquired during the transition of the electron from the initial ground state to the continuum and the influence of the streaking field on the resonant structure of the atom.\\[4pt] [1] J. Su et al., Phys. Rev. Lett. {\bf 113}, 263002 (2014);\\[0pt] [2] J. Su et al., Phys. Rev. A {\bf 88}, 023413 (2013);\\[0pt] [3] J. Su et al., Phys. Rev. A {\bf 89}, 013404 (2014). [Preview Abstract] |
Tuesday, June 9, 2015 2:24PM - 2:36PM |
C4.00003: Wigner-Smith time delay and its application to attosecond streaking Cory Goldsmith, Jing Su, Andreas Becker, Agnieszka Jaron-Becker Attosecond streaking experiments have been suggested as a means for observing temporal delays in photoemission, but the interpretation of the time delays observed in such experiments is still debated. Using a calculation of the streaking delays as a field-weighted sum over finite-range delays accumulated over the duration of the streaking pulse length [1], we provide further analysis into the role the Coulomb potential plays in the observed, so-called ``streaking delay." To this end, we make use of cut-off Coulomb and single active electron (SAE) potentials to calculate field-free Wigner-Smith-like time delays accumulated over small intervals of time to formulate an analytical model for the calculation of the streaking delays for hydrogenic atoms, as well as for SAE model potentials for noble gases. Our results indicate that in most cases, the influence of the streaking field on the short-range parts of the potential is a small effect. This allows for the representation of the streaking delay as the sum of the Wigner-Smith (WS) delay from scattering theory and the coupling between the streaking and Coulomb fields. [1] J. Su {\it et al.} Phys. Rev. A, \textbf{88}, 023413 (2013). [Preview Abstract] |
Tuesday, June 9, 2015 2:36PM - 2:48PM |
C4.00004: Influence of the Atomic Potential on Near-Threshold RABBITT Measurements Dietrich Kiesewetter, Stephen Schoun, Antoine Camper, Pierre Agostini, Louis DiMauro, Robert Jones We have used the RABBITT technique [P. M. Paul et al., Science 292, 1689 (2001)] to study IR-induced continuum transitions involving near-threshold, XUV photoelectrons from He, Ne, and Ar atoms. Energy exchange between ionized electrons and intense oscillating fields plays an essential role in many strong field physics phenomena. For large fields and/or electron energies, the parent ion plays a negligible role in the energy transfer process. This fact is exploited by RABBITT and attosecond streaking techniques for characterizing attosecond pulse trains and isolated pulses, respectively. However, for low energy electrons in weak to moderate dressing fields, the atomic potential influences the energy transfer process [E. S. Shuman et al. Phys. Rev. Lett. 101, 263001 (2008)], modifying the relative phase and amplitude of photoelectron sidebands in a RABBITT measurement (or the final momentum and apparent photoionization delay in a streaking experiment). For the RABBITT experiments, intense 1.3 micron pulses are used to generate the XUV harmonics for photoionization, and provide the phase-locked dressing field. In principle, the energy-dependence of the measured side-band amplitudes and phases might be used to extract information about the atomic binding potential. [Preview Abstract] |
Tuesday, June 9, 2015 2:48PM - 3:00PM |
C4.00005: Fullerene valence photoemission time delay near ionization cavity minima Maia Magrakvelidze, Dylan Anstine, Gopal Dixit, Mohamed Madjet, Himadri Chakraborty We investigate photoemission quantum phases and associated Wigner-Smith time delays for HOMO and HOMO-1 electrons of a C$_{60}$ molecule [1] using time-dependent local density approximation (TDLDA) [2]. The interference oscillations in C$_{60}$ valence emissions produce series of minima whose energy separation depends on the molecular size. We show that the quantum phase associated with these minima exhibits rapid variations due to electron correlations, causing rich structures in the photoemission time delay. Besides fullerenes, the detection of photoemission minima in metal clusters [3] suggests a possible universality of the phenomenon in cluster systems, or even quantum dots [4], that confine finite-sized electron gas. The work predicts a new research direction to apply attosecond metrology, such as RABITT, in the world of nanosystems. \\[4pt] [1] Magrakvelidze et al., arXiv:1409.2910 [physics.atm-clus]\\[0pt] [2] Madjet et al., PRA 81, 013202 (2010);\\[0pt] [3] Jaenkaelae et al., PRL 107, 183401 (2011);\\[0pt] [4] Chakraborty et al., arXiv:cond-mat/0111383. [Preview Abstract] |
Tuesday, June 9, 2015 3:00PM - 3:12PM |
C4.00006: Systematic Decomposition of Strong Field Spectra using Optical Phase Matching Zachary B. Walters, Daniel J. Haxton, C. William McCurdy Strong field transient absorption experiments measure the absorption or emission of energy from a broadband excitation laser pulse in the presence of an intense second pulse. Varying the time delay between the two pulses allows the effects of the intense field to be measured, yielding an experimental observable which may have a highly nonlinear dependence upon the parameters of the two fields. We apply optical phase matching conditions to decompose transient absorption spectra calculated using a nonperturbative multi configuration time dependent Hartree Fock (MCTDHF) code into a sum of multiphoton components, clarifying the role of recently identified light induced states in strong field photoabsorption. These results give a straightforward means of interpreting nonperturbative time dependent calculations, and suggest experimental methods for achieving these and similar goals. [Preview Abstract] |
Tuesday, June 9, 2015 3:12PM - 3:24PM |
C4.00007: Proposal for direct measurement of intense-field induced polarization in the continuum on the attosecond time scale using transient absorption C. William McCurdy, Daniel Haxton, Xuan Li A procedure is proposed for using transient absorption spectroscopy above the ionization threshold to measure the polarization of the continuum induced by an intense optical pulse. In this way transient absorption measurement can be used to probe sub-femtosecond intense field dynamics in atoms and molecules and extract the high frequency polarization that plays a central role in high harmonic generation. The method is based on a robust approximation to the dependence of these spectra on time-delay between an attosecond XUV probe pulse and an intense pump pulse that is verified over a wide range of intensities and time delays by all-electrons-active calculations using the Multiconfiguration Time-Dependent Hartree Fock method. To demonstrate the extraction of the field-induced polarization, we study the transient absorption spectrum of atomic Neon. [Preview Abstract] |
Tuesday, June 9, 2015 3:24PM - 3:36PM |
C4.00008: Quantum beats in attosecond time-resolved autoionization of krypton Yan Cheng, Michael Chini, Xiao-Min Tong, Andrew Chew, Julius Biedermann, Yi Wu, Eric Cunningham, Zenghu Chang The recent development of attosecond transient absorption spectroscopy (ATAS) has allowed probing of electron dynamics in atoms with few-femtosecond to sub-cycle time scales. Recently, the contribution of quantum beating to the two-color multi-photon excitation process has been proposed and demonstrated in the attosecond transient absorption experiment in the bound state of atoms. Here we performed an attosecond transient absorption experiment with krypton atoms, the attosecond pulse launched electronic wave packets composed of multiple bound excited states and spin-orbit coupling induced autoionization states of krypton atoms. Quantum beats were observed in the autoionizing states near the ionization threshold. Recurrences were observed in the 4s$^{2}$4p$^{5}(^{2}$P$^{\circ}$ $_{1/2})$6d, 4s$^{2}$4p$^{5}(^{2}$P$^{\circ}$ $_{1/2})$7d, 4s$^{2}$4p$^{5}(^{2}$P$^{\circ}$ $_{1/2})$8d states with periods of 5 -- 10 fs. The relative phase among these autoionizing states can be retrieved from such measurement, thus allowed the reconstruction of the valence state wave packets. [Preview Abstract] |
Tuesday, June 9, 2015 3:36PM - 3:48PM |
C4.00009: Molecular interferometer to decode attosecond electron-nuclear dynamics Alicia Palacios, Alberto Gonz\'alez-Castrillo, Fernando Martin A full characterization of the coupled electronic and nuclear dynamics in molecules is achieved by using an attosecond XUV-pump/XUV-probe scheme [Palacios et al., PNAS 111, 3973 (2014); Carpeggiani et al., Phys. Rev. A 89, 023420 (2014)]. The complete information on the wave packet generated by the pump pulse is obtained without introducing significant distortions through the pulses themselves. Theoretical ab initio calculations are presented for the hydrogen molecule, together with simple models for interpretation that can be easily extrapolated to larger systems. Different from the commonly used XUV-IR schemes, where the observed dynamics is typically dominated by the relatively strong IR field [Zhou et al., Nat Phys 8, 232 (2012); Dahlstr\"om et al., J. Phys. B 45, 183001 (2012)], XUV pulses of few-femtosecond and attosecond durations have been recognized as the ideal tool because their short wavelengths ensure a negligible distortion of the molecular potential. In the work presented here, the molecule is illuminated with twin XUV pulses with a given delay, creating a molecular interferometer due to electron ejection through both direct and sequential two-photon absorption leaving the molecule in the same final vibronic state. [Preview Abstract] |
Tuesday, June 9, 2015 3:48PM - 4:00PM |
C4.00010: Attosecond time--resolved streaked photoemission from solids Qing Liao, Uwe Thumm We established a quantum-mechanical model for infrared (IR) laser streaked photoelectron (PE) emission from metal solids by an ultrashort extreme ultraviolet (XUV) pulse [1]. Special emphasis was laid on the influence of the energy dispersion of PEs inside the solids on the photoemission time delay. We first applied this model to Mg(0001) surfaces, assuming free--electron dispersion and found good agreement with measured streaked PE spectra and streaking time delays [2,3]. Next, we investigate W(110) surfaces for which non--free PE dispersion must be included in order to reproduce the measured photoemission delays at different XUV central photon energies. Our model reproduces a series of measured streaked spectrograms and photoemission delays for different metal solids, including clean Mg(0001) and W(110) surfaces and Mg-covered W(110) surfaces. It incorporates modeling of the target band structure, electron mean free paths [3], energy dispersion, and screening of the IR laser field on the surface.\\[4pt] [1] U. Thumm, et al., in: Handbook of Photonics 1: ``Attosecond physics,'' ed. D. L. Andrew, ISBN:978-1-118-22553-0 (Wiley, 2015).\\[0pt] [2] Q. Liao and U. Thumm, Phys. Rev. Lett. 112, 023602 (2014).\\[0pt] [3] Q. Liao and U. Thumm, Phys. Rev. A 89, 033849 (2014). [Preview Abstract] |
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