Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session U05: Time-Resolved Electron Dynamics and Attosecond Spectroscopy |
Hide Abstracts |
Chair: Li Fang, University of Texas at Austin Room: Grand E |
Friday, June 1, 2018 8:00AM - 8:12AM |
U05.00001: Ultrafast Detection of Ring Currents in Molecules Tennesse Joyce, Agnieszka Jaron-Becker After interacting with a circularly polarized femtosecond laser pulse, atoms and molecules frequently exhibit persistent ring currents. The currents can be as strong as several milliamps, and they induce impressive local magnetic fields up to several Tesla. It has been conjectured that such currents could remain coherent for picoseconds or longer, although the prediction has not been verified experimentally. We discuss several schemes for attosecond time-resolved measurements of ring currents, which would provide a powerful tool for exploring the evolution of molecular symmetry and chirality. [Preview Abstract] |
Friday, June 1, 2018 8:12AM - 8:24AM |
U05.00002: High-harmonic Spectroscopy of Two-center Interference in Aligned OCS and CO2 Timothy Gorman, Timothy Scarborough, Peter Sandor, Sanjay Khatri, Francois Mauger, Paul Abanador, Robert Jones, Mette Gaarde, Kenneth Schafer, Pierre Agostini, Louis DiMauro We present high harmonic spectroscopic measurements on the spectral intensity and phase of two-center interferences resulting from laser-driven electron-core recollisions in OCS and CO2. Using a long-wavelength 1.3 um driving laser for high harmonic generation combined with impulsive molecular alignment we are able to reveal a change in both the sign and magnitude of the spectral phase jump between the two molecules. Additionally, we are able to control this interference by rotating the molecular axis relative to the laser polarization, demonstrating clear differences between the angular dependencies of the two molecules. Our study offers a precise comparison between molecular-frame interferences of polar and nonpolar molecules, potentially important for future studies of attosecond charge migration and coherent control of molecular processes. [Preview Abstract] |
Friday, June 1, 2018 8:24AM - 8:36AM |
U05.00003: A new time-dependent ab-initio close-coupling program for atomic ionization Luca Argenti, Tor Kjellsson Lindblom, Coleman Cariker, Thomas Carette, Eva Lindroth We present a time-dependent program to compute the photoionization of polyelectronic atoms by arbitrary light pulses. The program merges the capabilities of the Stock B-spline close-coupling structure code [1] with those of the time-dependent two-active-electron code described in [2]. It builds a close-coupling space in which multi-reference parent ions [3] are augmented with a spherical B-spline basis up to an assigned radius R. The initial state is evolved under the influence of external light pulses by solving the time-dependent Schroedinger equation with a second-order split-exponential propagator. Reflection at the box boundary is prevented by channel-specific complex-absorbers. The channel- and energy-resolved photoelectron spectrum is computed by projecting the wavefunction on a complete set of scattering states, after the external pulses are over. The program predictions are benchmarked against test simulations in helium [2], and applied to selected attosecond pump-probe simulations for the argon atom. [1] T Carette et al., Phys. Rev. A 87, 023420 (2013). [2] L Argenti and E Lindroth, Phys. Rev. Lett. 105, 053002 (2010). [3] C Froese-Fischer et al., Comp. Phys. Commun. 176, 559 (2007). [4] mcs.anl.gov/petsc. [Preview Abstract] |
Friday, June 1, 2018 8:36AM - 8:48AM |
U05.00004: Accurate reconstruction of the non-linear response of matter from spectro- scopic absorption data Stefan Donsa, Iva Brezinova, Joachim Burgdorfer, Veit Stooss, Stefano Cavaletto, Alexander Blattermann, Paul Birk, Christoph Keitel, Christian Ott, Thomas Pfeifer Observing the non-linear electronic response in atoms, molecules, and solids relies on precisely timed interactions with external stimuli. This, typically, requires the time-resolved recording of the response by a probe pulse following the excitation by the pump pulse as a function of the time delay between pump and probe. In this work we report on a new method to obtain time-resolved phase and amplitude information on the non-linear response using just the spec- troscopic data from one single-shot transient absorption measurement. In a proof of principle study we demonstrate the reconstruction of the non-linear dipole moment of doubly excited in Helium driven by an NIR laser pulse. We reconstruct the Rabi-flopping dynamics of the doubly excited states for a wide range of intensities. Comparing the experimental results with ab-initio calculations we are able to identify the states, which participate in the Rabi-flopping process. For stronger NIR intensities we observe that the field-induced ionization dominates over the auto-ionization indicating the break-down of frequently used few-state models. [Preview Abstract] |
Friday, June 1, 2018 8:48AM - 9:00AM |
U05.00005: Attosecond Transient Absorption Spectrum of Argon at the L$_{2,3}$-edge Andrew Chew, Nicolas Douguet, Coleman Cariker, Jie Li, Eva Lindroth, Xiaoming Ren, Yanchun Yin, Luca Argenti, Wendell Hill, Zenghu Chang Attosecond transient absorption, or time-resolved pump-probe spectroscopy, has made it possible to study fast electron dynamics in atomic and molecular systems within subfemtosecond timescales. With the emergence of table-top attosecond sources with spectra that extend into the water window, it is now possible to study atoms and molecules with absorption edges at higher energies than before. One such atom is the Argon L$_{2,3}$ edge, that lies near 250 eV, where the autoionization states approaching the 2p$^{-1}$ 2P$^{o}_{3/2}$ decay most notably through Auger processes. We present here the first Attosecond Transient Absorption Spectrum of the Argon atom in the vicinity of the 2p$^{-1}$ 2P$^{o}_{3/2}$ threshold, dressed by a strong shortwave infra-red pulse, with sub-cycle time resolution and high energy resolution. Our spectra resolve the dynamics of autoionizing states converging to the 2p$^{-1}$ 2P$^{o}_{3/2}$ threshold. Comparison with theoretical simulations indicates that the measured resonant profiles display ac-Stark shift and bear the signature of simultaneous Auger decay and tunneling ionization. [Preview Abstract] |
Friday, June 1, 2018 9:00AM - 9:12AM |
U05.00006: Physics with attosecond x-ray pulses Antonio Picon Resolving the real-time motion of carriers amongst valence and conduction band states provides the foundation for the development of materials with novel functionality and the advancement of modern electronics. Future studies using ultrafast capabilities with few-/sub-femtosecond x-ray transient absorption are essential to understand the optical response of materials in the early steps and unveil the role of electron-electron and electron-phonon scattering. Time-dependent approaches to describe these future experiments present challenging difficulties at the x-ray regime. In the recent years, we have developed in our group a novel theory based on the well-known Bloch equations that account for core electrons, allowing the description of x-ray spectroscopy experiments at the attosecond regime. Here we show recent theoretical results for semi metals systems. We revise some of these results and comment on future perspectives for studying the most fundamental electron-electron and electron-phonon interactions using attosecond x-ray spectroscopy. [Preview Abstract] |
Friday, June 1, 2018 9:12AM - 9:24AM |
U05.00007: Two-photon Ionization of Helium using the Complex Kohn Variational Method Nicolas Douguet, Barry Schneider, Luca Argenti The complex Kohn variational method [1,2] is extended to compute light-driven electronic transitions between continuum wavefunctions of an atomic or molecular system. This development enables the treatment of multiphoton processes in the perturbative regime. We present a proof of principles on two-photon ionization of ground and excited states of Helium induced by combining extreme ultra-violet (XUV) and near infrared (NIR) fields. The XUV pulse is tuned near the He($2s2p$)$^1P^o_1$ Feshbach resonance and the photoionization spectrum is compared with time-dependent calculations. The method is general and could for instance be used to study photoionization time-delay RABBITT experiments. [1] B. I. Schneider and T. N. Rescigno, Phys. Rev. A {\bf 37} 3749 (1988), [2] T. N. Rescigno, B. H. Lengsfield III, and C. W. McCurdy, {\it Modern Electronic Structure Theory 1} (World Scientific, Singapore, 1995). [Preview Abstract] |
Friday, June 1, 2018 9:24AM - 9:36AM |
U05.00008: Absolute phase reference for phase-dependent ionization of Rydberg states in strong microwave fields Eric Magnuson, Tom Gallagher The final energy of an electron excited to a continuum or high-lying Rydberg state in the presence of a strong microwave (MW) field is dependent on the phase $\phi_0$ of the MW field at which excitation occurs. Analogous to experiments using attosecond pulsed lasers to probe atoms and molecules in strong infra-red (IR) fields, exciting Rydberg states with a modulated IR laser have shown that ionization probability is strongly dependent on $\phi_0$. A classical model has been very useful in understanding these experiments, but the model's prediction that phase dependent ionization is greatest at an absolute phase of $\phi_0 = \pi/6$ had not yet been tested. To measure $\phi_0$ between the laser modulation and MW field, we excite the |54f> Rydberg state of Lithium with a phase modulated IR diode laser, while applying a MW field synchronous to the IR modulation and a DC field. The MW field causes the energy of the addressed state to oscillate, and the excitation probability will be greatest when the phase modulation of the laser and the energy modulation are in phase, providing an absolute reference for $\phi_0$. [Preview Abstract] |
Friday, June 1, 2018 9:36AM - 9:48AM |
U05.00009: Photoelectric effect in the time domain. Ruihua Xu, Xu Wang Photoelectric effect had almost exclusively been studied in the energy or momentum domain, which was of course adequate restricted to long laser pulse durations available then. With rapid advancements of ultrafast laser technologies, which enable the generation of laser pulses as short as a few tens of attoseconds, a time-domain (re-)study of photoelectric effect is of interest and highly desired. We present such a combined theoretical and numerical study in this presentation, and show how a photoelectron wave packet rapidly changes its shape in the real time space after being emitted, from a largely messy and irregular shape to a regular single-peak shape, within a “sizeable” time period depending on the length of the laser pulse. With a short few-cycle pulse, the photoelectric effect can be strikingly different from usual understandings obtained with long laser pulses. [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. |
© 2025 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