Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session H03: From Atto to ZeptoInvited Live
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Chair: Mette Gaarde, Louisiana State University |
Wednesday, June 2, 2021 8:00AM - 8:30AM Live |
H03.00001: Photoemission delays in molecules Invited Speaker: Alexandra Landsman Attosecond chronoscopy has revealed small but measurable delays in photoionization, characterized by the ejection of an electron on absorption of a single photon. Ionization-delay measurements in atomic targets provide a wealth of information about the timing of the photoelectric effect, resonances, electron correlations and transport. However, extending this approach to molecules presents challenges, such as identifying the correct ionization channels and the effect of the anisotropic molecular landscape on the measured delays. This talk will focus on some experimental measurements of ionization delays in molecules [1,2] and their theoretical interpretation using recently developed Classical Wigner Propagation (CWP) method. It will be shown how molecular ionization delays can be used to probe electron localization and molecular landscape. |
Wednesday, June 2, 2021 8:30AM - 9:00AM Live |
H03.00002: The travel time of light across a molecule Invited Speaker: Sven Grundmann In a recent experimental work, we addressed the question whether a spatially extended molecular orbital reacts simultaneously as a single unit on being hit by a photon. We used the P04 beamline at PETRA III (DESY) and applied a reaction microscope to investigate one-photon double ionization of the hydrogen molecule at 800 eV photon energy. We obtained the double-slit-like photoelectron interference pattern in the molecular frame of reference by measuring the three-dimensional momentum vectors of all reaction fragments. Depending on the angle between the photon propagation direction and the molecular axis, we found asymmetries in the interference pattern that can be interpreted as a result of the travel time of light across the molecular orbital, which is 247 zeptoseconds for the average bond length of molecular hydrogen. |
Wednesday, June 2, 2021 9:00AM - 9:30AM Live |
H03.00003: Ultrafast charge migration in molecules initiated by ionization and excitation Invited Speaker: Alexander I Kuleff Exposing molecules to ultrashort pulses results typically in a coherent population of several and even many electronic states. This triggers ultrafast electron dynamics, which may lead to a redistribution of the charge even before the nuclei start to move and adjust – a process often referred to as charge migration [1,2]. The non-adiabatic coupling between the electronic and nuclear motion will eventually destroy the initial electronic coherence and trap the migrating charge. The time during which the electron coherence is maintained is an important parameter. This time can be used to modulate the charge migration process and thus predetermine the succeeding nuclear rearrangement in the molecule – the paradigm of the emerging field of attochemistry. In this talk, fully quantum simulations of ultrafast charge dynamics initiated by both ionization [3] and excitation [4] of polyatomic molecules will be presented. Examples of decoherence and revival of coherences will be shown, as well as a transfer of electronic coherence through conical intersections [4]. The possibility to trace these dynamics by attosecond transient-absorption spectroscopy [5] will be discussed. |
Wednesday, June 2, 2021 9:30AM - 10:00AM On Demand |
H03.00004: Attosecond Transient Absorption Spectroscopy of Diatomic Molecules at 400 eV Invited Speaker: Jiro Itatani Intense ultrashort-pulse sources in long wavelength is crucial to extend the spectral range of high harmonic pulses from the extreme ultraviolet (EUV) to soft X-ray region. Optical parametric chirped pulse amplification (OPCPA) allows to produce intense IR pulses with a few-cycle duration with stable carrier-envelope phases (CEPs), which opens the route for attosecond transient absorption spectroscopy (TAS). We developed a CEP-stable ultrafast IR source (λ=1.6 μm, 1.5 mJ, 10 fs at 1 kHz) that used BiB 3 O 4 -based OPCPAs pumped by a Ti:sapphire chirped pulse amplification laser. Because of the extremely broad phase matching condition near the degeneracy, nearly one-octave parametric gain bandwidth is achieved. Using this source and a high-pressure gas cell filled with Ne or He gases, isolated attosecond pulses are successfully produced that almost cover the water window. We applied this soft X-ray source to trace field-driven dynamics of diatomic molecules, NO, via attosecond TAS at nitrogen K edge around 400 eV. Due to tunnel ionization of NO molecules, we observed the emergence and step-like increase of the 1s-2π absorption line of NO + ions. This line also showed a periodic shift due to molecular vibration. We also observed a signature of field-induced molecular alignment of NO and NO + . These results demonstrate the general capability of attosecond soft-X-ray TAS to trace various degrees of quantum dynamics (electronic, vibrational, and rotational) of different energy and time scales. |
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