Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session J05: Ultrafast and Strong-Field Processes in Clusters and NanoparticlesLive
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Chair: Uwe Thumm, Kansas State University Room: D139-140 |
Wednesday, June 3, 2020 2:00PM - 2:12PM Live |
J05.00001: Ionic Emission from Atomic Clusters in Intense Laser Pulses Abraham Camacho Garibay, Hyunwook Park, Zhou Wang, Pierre Agostini, Louis DiMauro For several years now, clusters have proved to be fascinating objects to explore and study intense light-matter interaction over a wide range of wavelengths. Their finite and controllable size allows to study the transition from molecules to the solid states, being able to efficiently absorb laser radiation and displaying a variety of interesting phenomena. When subjected to intense IR pulses, clusters emit fast electrons, highly charged and energetic ions, short wavelength photons and even neutrons. In this talk, I will focus on the well-known yet vexing phenomenon that is the anisotropy displayed in ionic emission, which has been experimentally observed to take place over a wide range of laser wavelengths and intensities. Through a combination of careful experiments and MD simulations, it will be possible to clearly understand the roles that Coulomb explosion, hydrodynamic expansion, atomic polarizability, wavelength and pulse length, jointly play to explain ionic emission. [Preview Abstract] |
Wednesday, June 3, 2020 2:12PM - 2:24PM Live |
J05.00002: Hot carrier dynamics in endohedral compounds Mohamed Madjet, Marcelo Carignano, Oriol Vendrell, Esam Ali, Himadri Chakraborty Using time-dependent density functional theory in combination with non-adiabatic molecular dynamical simulations$^{\mathrm{\thinspace }}$[1,2], the carrier dynamics in photoexcited endohedral fullerene is investigated. In order to identify the effect of many electron correlations, we performed two sets of simulations. The first one is based on a single particle approach$^{\mathrm{\thinspace }}$[1,3] that allows the study of large molecular and periodic systems. The second set is based on calculations performed taking into account many-body correlations only in the molecular systems$^{\mathrm{\thinspace }}$[4]. Results on electronic properties, optical excitation and ultrafast hot electron relaxation dynamics will be presented. The effect of different exchange-correlation (XC) functionals will be discussed. The advantages and drawbacks of the two methods will be outlined. [1] A. V. Akimov and O.V Prezhdo, \textit{J. Chem. Theory Comput.} \textbf{9}, 11 (2013); [2] Madjet \textit{et al.}, \textit{J. Phys. Chem. Lett.}\textbf{ 8}, 18 (2017); [3] Zapata \textit{et al. J. Chem. Inf. Model.} \textbf{59}, 3191 (2019); [4] Madjet \textit{et al. J. Chem. Phys.} \textbf{138}, 094311 (2013). [Preview Abstract] |
Wednesday, June 3, 2020 2:24PM - 2:36PM Live |
J05.00003: \textbf{Strong-field-ionization photoelectron imaging of metal nanoparticles } Erfan Saydanzad, Jianxiong Li, Jeffrey Powell, Adam Summers, Seyyed Javad Robatjazi, Philipp Rupp Rupp, Christopher M. Sorensen, Daniel Rolles, Matthias F. Kling, Carlos Trallero-Herrero, Artem Rudenko, Uwe Thumm We modeled strong-field ionization from metal nanoparticles by extending our classical-trajectory-sampling approach [1]. Our numerical model includes (i) photoelectron emission on the surface of the nanoparticle by an intense IR laser pulse and (ii) photoelectron propagation outside the nanosphere in the presence of the incident laser and induced plasmonic fields. It accountes for electron-electron- and electron-residual charge interactions and for electron rescattering at the nanoparticle surface. Based on simulated photoelectron-momentum distributions for 10 to 70 nm diameter gold nanospheres and three different intensities, and in comparison with measured velocity-map-image (VMI) photoelectron spectra [2], we scrutinize the effects of electronic correlation, induced plasmonic fields, and electron-residual charge interactions. [1] E. Saydanzad, J. Li, and U. Thumm, Phys. Rev. A 95, 053406 (2017). [2] J. Powell et al., ~Optics Express ~ 27, ~ 27124 (2019). [Preview Abstract] |
Wednesday, June 3, 2020 2:36PM - 2:48PM Live |
J05.00004: Tracking the non-linear optical response in plasmonic nanoparticles with strong-field photoemission spectroscopy Jeffrey Powell, Jianxiong Li, Adam Summers, Seyyed Javad Robatjazi, Michael Davino, Philipp Rupp, Chris Sorensen, Daniel Rolles, Matthias Kling, Carlos Trallero-Herrero, Uwe Thumm, Artem Rudenko The ability to reversibly manipulate the electronic structure and optical response of nanometer-sized metal and semiconductor structures at a femtosecond timescale holds strong promise to enhance our understanding of the transient electronic response of solid matter and enable novel applications in ultrafast electro-optical devices. In order to probe the transient optical response of such structures, we exposed solid gold nanospheres and gold spherical shells with silica cores to intense pulses of infrared light and measured the emitted photoelectrons. Comparing photoemission yields from these samples, we can relate the cut-off energy to the plasmonic dielectric response near the nanoparticle surfaces as a function of the incident-pulse intensity. Our measured intensity-dependent changes in the cut-off energy for emission from these nanoparticles is compatible with the onset of the non-linear response in gold. At low intensities, the cut-off energies of shelled particles greatly exceed the solid particles while at the highest intensities their responses are identical. This effectively constitutes an ultrafast optical switch. [Preview Abstract] |
Wednesday, June 3, 2020 2:48PM - 3:00PM Live |
J05.00005: Demonstration of a sub-Poissonian free electron emitter Sam Keramati, Will Brunner, T. J. Gay, Herman Batelaan Femtosecond-laser-driven nanotip electron sources have been widely studied in recent years. The relatively large spatial coherence lengths attainable through such point-like emitters, along with the possibility to drive them using ultrashort laser pulses to achieve high temporal resolution, have been the main incentives in this pursuit. The statistical distribution of the emitted photoelectrons has yet to be scrutinized experimentally. Furthermore, any hints of Pauli degeneracy pressure will be manifest in deviations from the steady-state emission statistics [1]. Implementing a double-detector coincidence technique, we inspected the photoelectron distribution originated from an electrochemically etched tungsten nanotip needle. The emitter was operated at room temperature with a near-IR Ti:Sapphire laser oscillator having few-nJ output pulses of duration 100 fs, at a repetition rate of 76 MHz. Contrary to the assumption that the emission must be random, we found that the photoemission distribution is manifestly sub-Poissonian for both sharp and broad tips with approximate geometrical radii of 50 nm and 400 nm, respectively. [1] S. Keramati, E. Jones, J. Armstrong, and H. Batelaan, In ``Advances in Imaging and Electron Physics'', Elsevier (2020), Vol. 213, Ch.1. [Preview Abstract] |
Wednesday, June 3, 2020 3:00PM - 3:12PM Live |
J05.00006: Ionization and trajectory control in strong-field photoemission from tungsten needle tips with a two-color laser field Philip Dienstbier, Timo Paschen, Lennart Seiffert, Thomas Fennel, Peter Hommelhoff Two-color laser fields with well-defined relative phase allow probing and controlling electronic dynamics on the sub-femtosecond time scale. With two-cycle fundamental pulses we can reach the strong-field regime of photoemission at nanometer sharp tungsten needle tips. When superimposing a weak second harmonic field, we expect a strong modulation of the emission yield\footnote{F\"{o}rster et al., PRL \textbf{117}, 217601 (2016)}$^{,}$\footnote{Paschen et al., J. Mod. Opt. \textbf{64}, 10-11, 1054 (2017)}, and, in the strong-field regime, also trajectory modifications\footnote{Seiffert et al., J. Phys. B. \textbf{51}, 134001 (2018)}. Here we show our experimental findings for field-driven and ionization-related electron dynamics in energy spectra as a function of the phase between fundamental and second harmonic. The comparison with time-dependent Schr\"{o}dinger equation and simple-man's model simulations shows excellent agreement. This allows us to define characteristic markers and use them to disentangle ionization from trajectory modifications, giving insight into the rescattering mechanism by the fundamental field alone and its modification by the second harmonic, in the nearfield and at the surface of a nanoscale needle tip. [Preview Abstract] |
Wednesday, June 3, 2020 3:12PM - 3:24PM Live |
J05.00007: Ultrafast Photoelectron Imaging of Energy Transfer Dynamics in Excited Doped Helium Nanodroplets Catherine Saladrigas, Christian Claudio, Nathan Helvy, Daniel M. Neumark, Oliver Gessner Doped helium nanodroplets are an excellent system to study solvent-dopant interactions. Droplets are a unique solvent that are both relatively simple in electronic structure, as compared to molecular solvents, and intriguing due to their superfluid ground state properties. We are interested in studying energy and charge transfer mechanisms from the excited droplet environment to dopant atoms and molecules, and how these mechanisms compete with internal droplet relaxation mechanisms. Energy transfer to a noble gas dopant in an electronically excited droplet has been observed in static experiments. With a sufficiently high droplet excitation energy, the energy transfer results in indirect ionization of the dopant. In a complimentary femtosecond time-resolved experiment, we want to gain a better understanding of the physics underlying the host-dopant energy transfer mechanisms. Using a high harmonic generated XUV pulse to electronically excite the droplet and a UV probe pulse to deplete the energy transfer signal, we can detect the photoelectrons produced from the energy transfer with velocity map imaging as a function of pump-probe time delay. Based on the modulation of the photoelectron spectrum at various time delays, we can gain information about the energy transfer mechanisms. [Preview Abstract] |
Wednesday, June 3, 2020 3:24PM - 3:36PM |
J05.00008: Enhancement of high-order harmonic generation from endohedrally confined atoms Turker Topcu, Erdi A. Bleda, Zikri Altun We describe a scheme in which by coupling exited atoms to fullerenes, one can demonstrably increase the harmonic conversion efficiency in HHG, adding to the toolbox of techniques used to increase photon intensities across the harmonic plateau. % We demonstrate this using an endohedrally confined hydrogen atom inside a C$_{60}$ cage, and consider three distinct physical situations in which the initial state is (1) entirely confined inside the C$_{60}$, (2) partially outside, and (3) mainly localized on the cage wall. We show that when the endofullerene system starts in a state with a classical turning point outside the C$_{60}$ shell, the high-harmonic photon yield can be enhanced up to 4 orders of magnitude. We will explain the underlying physical mechanisms in each case using fully three-dimensional quantum simulations. % We assess what fraction of the initial endofullerenes needs to survive the laser pulse in a macroscopic sample for a meaningful increase in the photon yield by propagating the generated harmonics through the mixed medium consisting of atoms and endofullerenes. [Preview Abstract] |
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