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 Q05: Strong Field Physics Involving Soft and Condensed Matter |
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Chair: Shambhu Ghimire, Stanford University Room: Grand E |
Thursday, May 31, 2018 8:00AM - 8:12AM |
Q05.00001: Direct interferometric measurement of coherence properties of high-harmonics from crystals Jian Lu, Eric Cunningham, YongSing You, David Reis, Shambhu Ghimire High-order harmonic generation in solids has emerged as a promising route to generate attosecond pulses and to probe electronic structure of bulk materials. The underlying dynamics are being debated in the form of relative role of inter- and intra-band electron dynamics. While the high density of solid-state media presents the potential for high efficiency, it also involves strong propagation effects to the driving laser pulse. As a result, the spatiotemporal properties of high-harmonics could be altered in a non-trivial manner. Here, we employ a robust homodyne spectroscopic method and measure coherence properties of extreme-ultraviolet high-harmonics from bulk MgO crystals. We record phase-stable interferograms of high-harmonics with good visibility, when two sources are identical. We watch how fringes move as we change the relative intensities. We perform measurements in both reflection and transmission geometry such that we can quantify propagation effects. From the fringe shift, we retrieve intensity-dependent emission phase of individual harmonics, consistent to the inter-band model. Our results provide solid foundation for attosecond pulse metrology based on a novel high-harmonic generation technique. [Preview Abstract] |
Thursday, May 31, 2018 8:12AM - 8:24AM |
Q05.00002: High-harmonic generation in solids with and without topological edge states Dieter Bauer, Kenneth Hansen, Helena Dr\"ueke High-harmonic generation (HHG) in the two topological phases of a finite, one-dimensional, periodic structure is investigated using a self-consistent time-dependent density functional theory (TDDFT) approach. For harmonic photon energies smaller than the band gap, the harmonic yield is found to differ up to fourteen orders of magnitude for the two topological phases. This giant topological effect is explained by the degree of destructive interference in the harmonic emission of all valence-band (and edge-state) electrons, which strongly depends on whether topological edge states are present or not. The combination of strong-field laser physics with topological condensed matter opens up new possibilities to control electronically strong-field-based light or particle sources or---vice versa---to steer by all optical means topological electronics. [Preview Abstract] |
Thursday, May 31, 2018 8:24AM - 8:36AM |
Q05.00003: Anisotropic Polarization Dependence of High Harmonic Generation in BaTiO$_{\mathrm{3}}$ Shima Gholam Mirzaeimoghadar, Erin Crites, John Beetar, Aiping Chen, Michael Chini Following the first observation of high-order harmonic generation (HHG) from bulk ZnO at 2011, it has become clear that the properties of the solid can strongly influence the generated harmonics. For example, the generation of even harmonics has been investigated in non-centrosymmetric crystals, and anisotropy in the polarization states of emitted harmonics has been observed in both asymmetric and symmetric crystals. Here, we study mid-IR driven high harmonic generation from the ferroelectric crystal BaTiO$_{\mathrm{3}}$, for which external field control of the spontaneous polarization may allow control over the harmonic generation process. We observe anomalous behavior in both the yield and the polarization states of odd and even harmonics when rotating the input polarization relative to the crystal axes, potentially suggesting an important role of the crystal's Berry curvature on the HHG process. [Preview Abstract] |
Thursday, May 31, 2018 8:36AM - 8:48AM |
Q05.00004: THz enhanced surface Second Harmonic Generation Sanjay Khatri, Robert Jones When a material is exposed to an intense laser field, the absence of inversion symmetry at the surface can result in the formation of a non-linear surface polarization and surface second harmonic (SSH) emission. We find that the SSH yield from a metal can be dramatically influenced by the presence of an additional THz field. In the experiments, collinear 100fs 780nm laser and 2ps single-cycle THz beams are focused at grazing incidence along a gold surface. The SSH yield is measured as a function of the THz intensity, relative laser-THz delay, and laser/THz polarizations relative to the surface normal. The yield from an optically flat gold mirror increases by as much as a factor of three in the presence of a 50kV/cm THz field. Interestingly, the SSH enhancement for the same THz field is as large as a factor of 15 if the gold mirror is replaced by a gold-coated diffraction grating, apparently due to either a local THz field enhancement or increased sensitivity of the non-linear polarization to the THz field near grating micro-structures. We are exploring the use of THz-enhanced SSH emission to characterize the THz-field enhancement and/or response of micro-structured metal surfaces with other geometries. [Preview Abstract] |
Thursday, May 31, 2018 8:48AM - 9:00AM |
Q05.00005: Imaging plasmonic fields with atomic spatiotemporal resolution Jianxiong Li, Erfan Saydanzad, Uwe Thumm We propose a scheme for the reconstruction of plasmomic fields at isolated nanoparticles from infrared-streaked extreme-ultraviolett photoemission spectra. Based on quantum-mechanically modeled spectra [1,2], we demonstrate and analyze the accurate imaging of the IR-streaking-pulse-induced transient plasmonic fields at gold nanospheres with sub-femtosecond temporal and sub-nanometer spatial resolution [3]. [1] J. Li, E. Saydanzad, and U. Thumm, Phys. Rev. A \textbf{94}, 051401(R) (2016). [2] J. Li, E. Saydanzad, and U. Thumm, Phys. Rev. A \textbf{95}, 043423 (2017). [3] J. Li, E. Saydanzad, and U. Thumm, submitted. [Preview Abstract] |
Thursday, May 31, 2018 9:00AM - 9:12AM |
Q05.00006: Spatiotemporal imaging of plasmonic fields near metallic nanoparticles beyond the diffraction limit Erfan Saydanzad, Jianxiong Li, Uwe Thumm Optically induced collective conduction electron oscillations can generate intense plasmonic field near nanoparticles [1, 2]. Based on simulated streaked photoemission spectra, we suggest a method for reconstructing nanoplasmonic fields near metal nanospheres with nm spatial and sub-fs temporal resolution. We apply this imaging scheme to Au nanospheres and scrutinize the accuracy of the spatiotemporally reconstructed plasmonic near-field distributions in comparison with a directly calculated plasmonic field using Mie theory [3]. [1] E. Saydanzad, J. Li, and U. Thumm, Phys. Rev. A \textbf{95}, 053406 (2017) [2] J. Li, E. Saydanzad, and U. Thumm, Phys. Rev. A \textbf{94}, 051401(R) (2016); Phys. Rev. A \textbf{95}, 043423 (2017). [3] E. Saydanzad, J. Li, and U. Thumm, in preparation. [Preview Abstract] |
Thursday, May 31, 2018 9:12AM - 9:24AM |
Q05.00007: Photoelectron emission from metal and dielectric nanoparticles in intense laser fields Jeffrey Powell, Seyyed Javad Robatjazi, Adam Summers, Matthias Kling, Artem Rudenko Nanoparticles provide a unique platform to study the mechanisms of light interactions with complex systems, in particular, the motion of electrons driven by strong fields and excitation of plasmonic resonances. Here we report on the systematic analysis of the photoelectron emission from single, isolated, gas-phase, spherical nanoparticles as a function of particle size, composition and laser intensity. Gold, silica (SiO$_{\mathrm{2}})$, and silica core/gold shell nanoparticles ranging in size from 5nm to 750nm were irradiated by 800nm, 25fs laser pulses at 0.2-20 TW/cm$^{\mathrm{2}}$ peak intensities. A high energy velocity-map imaging spectrometer was used to determine the cutoff photoelectron energy for each sample and intensity. Nanoparticle size and composition influence the electron cutoff energy, which provides insight into photoelectron trajectories and rescattering dynamics, both of which are affected by near-field enhancement and plasmonic excitation. In particular, we observe that photoelectrons emitted from gold nanoparticles are much more energetic than those from silica, which, in turn, are much faster than those from isolated atoms or molecules exposed to the same light pulses. [Preview Abstract] |
Thursday, May 31, 2018 9:24AM - 9:36AM |
Q05.00008: Time-resolved photoelectron spectroscopy of Ag(111) and Au(111) surfaces Marcelo Ambrosio, Uwe Thumm Upon illumination of transition metal surfaces with an XUV pulse train and a time-delayed phase-coherent IR pulse, recent experiments [1-3] have applied the RABBITT (reconstruction of attosecond beating by interference of two-photon transitions) technique to provide time-resolved information about the photoemission processes on surfaces. We simulated RABBITT spectra within a quantum-mechanical model, calculating the transition matrix element in the non-dipole velocity gauge between tight-binding initial and a modified-Volkov final states [4] and adjusting the substrate parameters to measured energy-resolved spectra for normal emission [5]. We compare our numerically modeled RABBITT spectra with experimental spectra obtained by Locher \textit{et al}. [1] for Ag(111) and Au(111) surfaces, accounting for electrons scattered through the substrate during the emission process by including a delay-independent photoelectron background [6]. [1] R. Locher \textit{et al.}, Optica \textbf{2}, 405 (2015). [2] Z. Tao \textit{et al.}, Science \textbf{353}, 62 (2016). [3] M. Lucchini \textit{et al.,} Phys. Rev. Lett. \textbf{115}, 137401 (2015). [4] M. J. Ambrosio and U. Thumm, Phys. Rev. A \textbf{96}, 051403 (2017). [5] F. Roth \textit{et al.} J. Electron. Spectrosc. Relat. Phenom., in press (2017). [6] M. J. Ambrosio and U. Thumm, in preparation. [Preview Abstract] |
Thursday, May 31, 2018 9:36AM - 9:48AM |
Q05.00009: A theoretical model of the ``Transverse Optical Magnetism" phenomenon Chitra Rangan, Christopher Diloreto In famous scattering experiments [1,2], high-intensity, short-duration, electromagnetic pulses were scattered off dielectric liquids such as water and carbon tetrachloride. The observed pattern of the scattered light led the authors to propose that there was magnetic dipole radiation generated. They called this phenomenon ``transverse optical magnetism". There has been no satisfactory theoretical explanation for this phenomenon. We have recently demonstrated that a dense ensemble of two-level atoms driven by an electromagnetic field can be modelled by an effective single quantum system that has a time-varying decoherence rate [3]. We use this model to provide an elegant theoretical explanation for the experiments. We show that the radiation pattern suggestive of magnetic dipole scattering occurs naturally when the inter-particle interactions caused due to spontaneous emission from individual atoms are taken into account in 3-dimensions. Our effective single particle model's predictions match very well with experimental data. [1] S.L. Oliveira and S. C. Rand, Phys. Rev. Lett. 98:093901, 2007. [2] S. C. Rand, W.M. Fisher, and S. L. Oliveira, J. Opt. Soc. Am B 25:1106, 2008. [3] C. S. DiLoreto and C. Rangan, Phys. Rev. A 97: 013812, 2018. [Preview Abstract] |
Thursday, May 31, 2018 9:48AM - 10:00AM |
Q05.00010: Ultrafast Dynamics of Ionized Tryptophan in Aqueous Solution via Few-Femtosecond Transient Absorption Spectroscopy Muhammad Shafiq Bin Mohd Yusof, Tushar Debnath, Zhi Heng Loh Few-femtosecond optical transient absorption spectroscopy elucidates ionization-induced vibrational coherences and ultrafast dynamics of small biomolecules in aqueous solution. Strong-field ionization of tryptophan (Trp) in basic medium by intense, few-cycle ($\sim$ 6-fs) laser pulses yields the tryptophan radical and the hydrated electron. The tryptophan radical appears at $\sim$ 580 nm in the transient absorption spectrum, overlapping with the broad absorption of the hydrated electron in the visible region. The ultrafast dynamics and vibrational coherences of the tryptophan radical will be presented. [Preview Abstract] |
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