Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session T2: Invited Session: Attosecond DynamicsInvited
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Chair: Andre Bandrauk, Universite de Sherbrooke Room: Ballroom B |
Friday, May 27, 2016 8:00AM - 8:30AM |
T2.00001: Attosecond dynamics of electrons in molecules and liquids Invited Speaker: Hans Jakob Woerner The ultrafast motion of electrons and holes following light-matter interaction is fundamental to a broad range of chemical and biophysical processes. In this lecture, I will discuss two recent experiments carried out in our group that measure the atomic-scale motion of charge with attosecond temporal resolution (1 as = 10$^{-18}$ s). The first experiment is carried out on isolated, spatially oriented molecules in the gas phase. We advance high-harmonic spectroscopy to resolve spatially and temporally the migration of an electron hole immediately following ionization of iodoacetylene, while simultaneously demonstrating extensive control over the process. A multidimensional approach, based on the measurement of both even and odd harmonic orders, enables us to reconstruct both quantum amplitudes and phases of the electronic states with a resolution of $\sim$100 as. We separately reconstruct quasi-field-free and laser-controlled charge migration as a function of the spatial orientation of the molecule and determine the shape of the hole created by ionization \footnote{P. M. Kraus, B. Mignolet, D. Baykusheva, A. Rupenyan, L. Horny, E. F. Penka, G. Grassi, O. I. Tolstikhin, J. Schneider, F. Jensen, L. B. Madsen, A. D. Bandrauk, F. Remacle, and H. J. W\"orner, \textit{Science}~\textbf{350}, 790 (2015)}. The second experiment is carried out on a free-flowing microjet of liquid water. We use an attosecond pulse train synchronized with a near-infrared laser pulse to temporally resolve the process of photoemission from liquid water using the RABBIT technique. We measure a delay on the order of 50 as between electrons emitted from the HOMO of liquid water compared to that of gas-phase water and a substantially reduced modulation contrast of the corresponding sidebands. Since our measurements on solvated water molecules are referenced to isolated ones, the measured delays reflect (i) the photoionization delays caused by electron transport through the aqueous environment and (ii) the effect of solvation on the parent molecule. The relative modulation contrast, in turn, contains information on (iii) the modification of transition amplitudes and (iv) dephasing processes. These experiments make the liquid phase and its fascinating mechanisms accessible to attosecond science \footnote{I. Jordan, M. Huppert, A. von Conta, L. Seiffert, M. Arbeiter, Th. Fennel and H.J. W\"orner, \textit{to be published}}. [Preview Abstract] |
Friday, May 27, 2016 8:30AM - 9:00AM |
T2.00002: Applications of Elliptically Polarized, Few-Cycle Attosecond Pulses Invited Speaker: Anthony F Starace Use of elliptically-polarized light opens the possibility of investigating effects that are not accessible with linearly-polarized pulses. This talk presents two new physical effects that are predicted for ionization of the helium atom by few-cycle, elliptically polarized attosecond pulses. For double ionization of He by an intense elliptically polarized attosecond pulse, we predict a nonlinear dichroic effect (i.e., the difference of the two-electron angular distributions in the polarization plane for opposite helicities of the ionizing pulse) that is sensitive to the carrier-envelope phase, ellipticity, peak intensity $I$, and temporal duration of the pulse\footnote{J.M. Ngoko Djiokap, N.L. Manakov, A.V. Meremianin, S.X. Hu, L.B. Madsen, and A.F. Starace, “Nonlinear dichroism in back-to-back double ionization of He by an intense elliptically-polarized few-cycle XUV pulse,” Phys. Rev. Lett. \textbf{113}, 223002 (2014).}. For single ionization of He by two oppositely circularly polarized, time-delayed attosecond pulses we predict that the photoelectron momentum distributions in the polarization plane have helical vortex structures that are exquisitely sensitive to the time-delay between the pulses, their relative phase, and their handedness\footnote{J.M. Ngoko Djiokap, S.X. Hu, L.B. Madsen, N.L. Manakov, A.V. Meremianin, and A.F. Starace, “Electron Vortices in Photoionization by Circularly Polarized Attosecond Pulses,” Phys. Rev. Lett. \textbf{115}, 113004 (2015).}. Both of these effects$^{2, 3}$ manifest the ability to control the angular distributions of the ionized electrons by means of the attosecond pulse parameters. Our predictions are obtained numerically by solving the six-dimensional two-electron time-dependent Schr\"{o}dinger equation for the case of elliptically polarized attosecond pulses. They are interpreted analytically by means of perturbation theory analyses of the two ionization processes$^{2, 3}$. [Preview Abstract] |
Friday, May 27, 2016 9:00AM - 9:30AM |
T2.00003: Non-linear attosecond and femtosecond probes of chiral structures and dynamics Invited Speaker: Olga Smirnova We will consider non-linear approaches to probing chiral structures and dynamics using two complementary types of measurements: high harmonic generation and photoelectron spectroscopy. Chiral discrimination with high harmonic generation (cHHG method) has been introduced in our recent work [1]. In its original implementation, the cHHG method works by detecting high harmonic emission from randomly oriented ensemble of chiral molecules driven by elliptically polarized field, as a function of ellipticity. Ref [1] also used the high harmonic spectra to resolve the electronic chiral response with 0.1 femtosecond temporal resolution. We will discuss future perspectives in the development of this novel method, the ways of increasing chiral dichroism using tailored laser pulses, new detection schemes involving high harmonic phase measurements, and concentration-independent approaches to chiral discrimination. We will then discuss physical origins of chiral dichroism in femtosecond pump-probe schemes focussing on detection of photoelectrons and consider the role of bound and continuum state chirality, the possibility to distinguish between them and present a simple physical picture which allows one to predict the strength of chiral response and understand the salient interplay of bound and continuum chiral contributions. We will also show how intrinsic and extrinsic chirality can serve as a sensitive probe of electronic and vibrational coherence. [1] R. Cireasa et al, Nature Physics 11, 654, 2015 [Preview Abstract] |
Friday, May 27, 2016 9:30AM - 10:00AM |
T2.00004: Attosecond probing of state-resolved ionization and superpositions of atoms and molecules. Invited Speaker: Stephen Leone Isolated attosecond pulses in the extreme ultraviolet are used to probe strong field ionization and to initiate electronic and vibrational superpositions in atoms and small molecules. Few-cycle 800 nm pulses produce strong-field ionization of Xe atoms, and the attosecond probe is used to measure the risetimes of the two spin orbit states of the ion on the 4d inner shell transitions to the 5p vacancies in the valence shell. Step-like features in the risetimes due to the subcycles of the 800 nm pulse are observed and compared with theory to elucidate the instantaneous and effective hole dynamics. Isolated attosecond pulses create massive superpositions of electronic states in Ar and nitrogen as well as vibrational superpositions among electronic states in nitrogen. An 800 nm pulse manipulates the superpositions, and specific subcycle interferences, level shifting, and quantum beats are imprinted onto the attosecond pulse as a function of time delay. Detailed outcomes are compared to theory for measurements of time-dynamic superpositions by attosecond transient absorption. [Preview Abstract] |
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