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 B4: Focus Session: Attosecond Dynamics in Atoms and Molecules |
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Chair: Alicia Palacios, Universidad Autonoma de Madrid Room: Union DE |
Tuesday, June 9, 2015 10:30AM - 11:00AM |
B4.00001: Attosecond Delays in Resonant Photoionization Invited Speaker: Alfred Maquet Attosecond delays in the photoionization of atomic states have been evidenced in recent experiments performed in the 2010's [1, 2]. The delays were associated to the emission of photoelectron wave packets ejected from different atomic states, in the combined presence of attosecond pulses of XUV radiation and of a synchronized IR laser pulse, the latter being used as a reference ``clock'' [3]. These experiments were performed at XUV frequencies connecting the ground state to a ``flat'' continuum. Theoretical treatments were able to relate the measured delays to Wigner's definition of time delays in terms of the energy derivative of the phase-shift attached to the continuum wave functions of the photoelectrons [4]. Attention has recently shifted towards the case of resonant photoionization in the course of which the XUV frequency is tuned close to a resonance of the target system. The case of a transition towards an autoionizing states of the target is particularly interesting as it makes evident the role of electronic correlations [5]. Here, we shall present recent advances realized in the theoretical interpretation of this new class of experiments. \\[4pt] [1] M. Schultze et al. Science \textbf{328}, 1658-1662 (2010).\\[0pt] [2] K. Kl\"{u}nder, et al. Phys. Rev. Lett. \textbf{106}, 143002 (2011) 5 p.\\[0pt] [3] A. Maquet, J. Caillat, and R. Ta\"{i}eb, J. Phys. B: At. Mol. Opt. Phys. \textbf{47,} 204004 (2014) 13 p.\\[0pt] [4] E. P. Wigner, Phys. Rev. \textbf{98}, 145-7 (1955).\\[0pt] [5] Christian Ott, et al. $ s$Nature \textbf{516}, 374-378 (2014). [Preview Abstract] |
Tuesday, June 9, 2015 11:00AM - 11:30AM |
B4.00002: Towards attosecond measurement in molecules and at surfaces Invited Speaker: Jonathan Marangos \begin{itemize} \item We will present a number of experimental approaches that are being developed at Imperial College to make attosecond timescale measurements of electronic dynamics in suddenly photoionized molecules and at surfaces. A brief overview will be given of some of the unanswered questions in ultrafast electron and hole dynamics in molecules and solids. These questions include the existence of electronic charge migration in molecules and how this process might couple to nuclear motion even on the few femtosecond timescale. How the timescale of photoemission from a surface may differ from that of an isolated atom, e.g. due to electron transport phenomena associated with the distance from the surface of the emitting atom and the electron dispersion relation, is also an open question. \item The measurement techniques we are currently developing to answer these questions are HHG spectroscopy, attosecond pump-probe photoelectron/photoion studies, and attosecond pump-probe transient absorption as well as attosecond streaking for measuring surface emission. We will present recent advances in generating two synchronized isolated attosecond pulses at different colours for pump-probe measurements (at 20 eV and 90 eV respectively). Results on generation of isolated attosecond pulses at 300 eV and higher photon energy using a few-cycle 1800 nm OPG source will be presented. The use of these resources for making pump-probe measurements will be discussed. \end{itemize} Finally we will present the results of streaking measurement of photoemission wavepackets from two types of surface (WO$_{3}$ and a evaporated Au film) that show a temporal broadening of $\sim$ 100 as compared to atomic streaks that is consistent with the electron mean free path in these materials. [Preview Abstract] |
Tuesday, June 9, 2015 11:30AM - 11:42AM |
B4.00003: Theoretical interpretation of attosecond transient absorption experiments on diatomics in O$_2$ Xuan Li, Daniel J. Haxton, C. William McCurdy We study the features in the XUV attosecond transient absorption spectrum that have been recently observed by Arvinder et al. (Phys. Rev. Lett. 109, 173001 (2012)) by using the fixed nuclei approximation and a recently developed implementation of the multiconfiguration time-dependent Hartree Fock (MCTDHF) method. We find that there is a one-to-one correspondence between the magnitude of the Fano q parameter of the resonances corresponding to the autoionizing Rydberg series and the sign of the change in their photo absorption intensity in the transient absorption experiment that depends on the time delay of a near-infrared (NIR) pulse. The calculated transient absorption spectrum and these features of the experiment can be explained using a few-level model in combination of a sudden approximation where the XUV-induced polarization is instantly extinguished by the intense NIR field. [Preview Abstract] |
Tuesday, June 9, 2015 11:42AM - 11:54AM |
B4.00004: Molecular Self-Probing Spectroscopy with High Harmonic Generation at Long Wavelengths A. Camper, S.B. Schoun, P. Agostini, Pascal Salieres, J. Caillat, R.R. Lucchese, L. DiMauro We used laser driven sub-femtosecond electronic wave packet (EWP) recollision to generate high-order harmonics (HHG) of a 1.3 $\mu$m laser pulse in aligned molecules. We performed a tomographic investigation of N$_{2}$ [ItataniNature2004, HaesslerNatPhys2010, VozziNatPhys2011, DivekiNJP2012] by characterizing the HHG yield and spectral phase of the attosecond emission for different recollision angles of EWP with respect to the main axis of the angular distribution of the molecules. Thanks to the high degree of alignment and to the fine spectral sampling, our XUV quantum phase measurements [SchounPRL2014] reveal subtle features in the recombination dipole moment of N$_{2}$. We interpret the latter within the Quantitative Rescattering Theory [LePRA2009] and emphasize the effect of the EWP scattering on the ion Coulombic potential and of the shape resonance in the X channel of N$_{2}$ on HHG [LucchesePRA1982]. Compared to previous results at 800 nm, our experiment is deeper into the tunneling regime and only one ionization channel is enough to explain what we observed. Our results shine a new light on imaging molecular orbitals using laser-driven photo-recombination processes. [Preview Abstract] |
Tuesday, June 9, 2015 11:54AM - 12:06PM |
B4.00005: Mapping and Controlling Ultrafast Dynamics of Highly Excited D2$+$ by Attosecond XUV Radiation Predrag Ranitovic, C. Hogle, L. Martin, R.Y. Bello, A. Palacios, J.L. Sanz-Vicario, F. Mart\'In, Xiao-Min Tong, M. Murnane, H. Kapteyn We show how spectrally tailored attosecond extreme ultraviolet and femtosecond infrared radiation can be used to coherently populate, map and control dynamics of highly excited states of D$_{\mathrm{2}}^{\mathrm{+}}$ that rapidly dissociate. In particular, we used a 43 eV XUV and a weak IR beam to coherently populate highly excited electronic states of D2$+$ through one- and two-photon absorption processes. By using time-delayed probe laser pulses and 3D momentum imaging in a COLTRIMS geometry, we show how the dissociation can be mapped and controlled on attosecond time scales using Coulomb-explosion imaging. We found that the major excitation channel, dissociating to the n$=$2 limit, perpendicular to the XUV/IR radiation, is not the 2pPi\textunderscore u, as discussed in literature, but the 2s Sigma\textunderscore g. [Preview Abstract] |
Tuesday, June 9, 2015 12:06PM - 12:18PM |
B4.00006: Imaging nonadiabatic laser-driven electron transient localization through high-order harmonic spectroscopy Michelle Miller, Agnieszka Jaron-Becker, Andreas Becker Theoretical predictions and indirect experimental observation hint that electrons within molecular systems can undergo highly nonadiabatic and transient localization on a sub-field cycle timescale. Direct observation of this rapid behavior is experimentally challenging, but would enable insights into laser-driven electron behavior on an attosecond time scale. In this theoretical study, we present and analyze signatures of intramolecular electron dynamics imprinted upon the molecular high-order harmonic generation (MHOHG) and above threshold ionization spectra of H$_2^+$ driven by mid-infrared wavelength light at moderate intensity and extended internuclear distances. We relate structural minima within the MHOHG spectrum and non-odd harmonic generation to electron dynamics at the time of ionization, demonstrating that the transient localization of the electron upon the counterintuitive nucleus results in the modulation of the radiated signal, allowing for the tracking of electron dynamics with sub-field cycle temporal resolution. [Preview Abstract] |
Tuesday, June 9, 2015 12:18PM - 12:30PM |
B4.00007: Time-resolving Attosecond Chiral Dynamics in Molecules with High Harmonic Spectroscopy O. Smirnova, R. Cireasa, A. Boguslavskiy, B. Pons, M.C.H. Wong, D. Descamps, S. Petit, H. Ruf, N. Thire, A. Ferre, J. Suarez, B. E. Schmidt, J. Higuet, A. F. Alharbi, F. Legare, V. Blanchet, B. Fabre, S. Patchkovskii, Y. Mairesse, R. Bhardwaj We demonstrate extreme chiral sensitivity of high harmonic generation from randomly oriented ensemble of chiral molecules in elliptical mid-infrared fields, and explain the physical mechanism underlying this very strong chiro-optical response. We also use the high harmonic spectra to follow the electronic chiral response with 0.1 femtosecond resolution. We studied two chiral molecules, epoxypropane and fenchone in 1.8 um, 50 fs, mid-10$^{\mathrm{13}}$ W/cm$^{\mathrm{2}}$ pulses. Very small ellipticity of the incident light, about 1{\%} in the field, is sufficient to induce several percent difference between the high harmonic response of left and right enantiomers. The origin of this effect lies in chiral-sensitive dynamics of the hole created by strong field ionization. Small differences in this dynamics between ionization and recombination are recorded and amplified by several orders of magnitude in high harmonic spectra. Using time-energy mapping we reconstruct sub-femtosecond chiral dynamics and show that the standard measure of the chiral signal is directly proportional to the recombination amplitude to the chiral-sensitive component of the hole wave-packet. [Preview Abstract] |
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