Bulletin of the American Physical Society
50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 64, Number 4
Monday–Friday, May 27–31, 2019; Milwaukee, Wisconsin
Session V03: FOCUS: Ultrafast processes in Condensed Matter, Nano-structures, and Clusters |
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Chair: Marco Taucer, National Research Council Canada Room: Wisconsin Center 101CD |
Friday, May 31, 2019 8:00AM - 8:30AM |
V03.00001: Photoemission from solid surfaces and nanoparticles with attosecond-nanometer spatiotemporal resolution. Invited Speaker: Uwe Thumm Attosecond time-resolved spectroscopy applies ultrashort attosecond XUV pulses (or pulse trains) to emit electrons into the field of delayed IR laser pulses. Over the past two decades this technique has matured to a powerful method for investigating the electronic dynamics in atoms [1] and is now being transferred to the scrutiny of electronic excitations, electron propagation, and collective electronic effects in solids [1-4] and plasmonic nanoparticles [1,5-7]. Compared with photoemission from isolated gaseous atoms, numerical simulations of such experiments on complex targets require, in addition, the adequate modeling of (i) the target's electronic band structure [1-4], (ii) elastic and inelastic scattering of released photoelectrons inside the solid [2-6], (iii) surface and bulk collective electronic excitations [5-7], (iv) the screening and reflection of the assisting IR-laser field at the solid surface [4], (v) the influence of equilibrating residual charge distributions on emitted photoelectrons [1], and (vi) the effect of spatially inhomogeneous plasmonic fields on the photoemission process [3,5-7]. I will address the extent to which photoelectron propagation in matter and the plasmonic response of nanostructures can be (a) represented in classical [1,6] and quantum mechanical [1-5] simulations and (b) retrieved in IR-streaked XUV [3,6-7] and IR-XUV two-photon interference (RABBITT) [2,4] photoemission spectra. [1] U. T. et al., in: Handbook of Photonics, Vol. 1, (Wiley 2015). [2] C. Chen et al., Proc. Natl. Acad. Sci. 114, E5300 (2017). L. Kasmi et al., Optica 4, 1492 (2017). [3] Q. Liao, and U. T., Phys. Rev. A 89, 033849 (2014); ibid. 92, 031401(R) (2015). [4] M. J. Ambrosio and U. T., Phys. Rev. A 96, 051403 (2017); ibid. 97, 043431 (2018). [5] J. Li, E. Saydanzad, and U. T., Phys. Rev. A 94, 051401(R) (2016); ibid. 95, 043423 (2017). L. Seifert et al., Nat. Phys. 13, 766 (2017). [6] E. Saydanzad, J. Li, and U. T., Phys. Rev. A 95, 053406 (2017); 98, 063422 (2018). [7] J. Li, E. Saydanzad, and U. T., Phys. Rev. Lett. A 120, 223903 (2018). [Preview Abstract] |
Friday, May 31, 2019 8:30AM - 9:00AM |
V03.00002: Nanoscale control of high-harmonic generation from solids Invited Speaker: Giulio Vampa Borrowing concepts from gas-phase experiments, high-harmonic emission from solids is thought to benefit from the high density of the target. However, high density comes at the price of high absorption of above-bandgap high-harmonics – the absorption length can be as short as few nanometers. As a result, high-harmonics have an extremely short emission depth: of the hundreds of microns that generate high-harmonics, only a tiny fraction (a few nanometers!) contributes to the measured high-harmonic signal. We have been using nanoscale structured surfaces to extract high-harmonics from deeper in the material, thereby overcoming the major limitation to the flux of above-bandgap high-harmonics.\\ \\ In my talk I will show how to shape the material at the nanoscale to extract high-harmonics from depths as high as 1 um – currently limited by the sample thickness, a great improve over 10 nm of the bulk material. I’ll show that our structures generate a high-harmonic flux which exceeds that of the un-patterned surface, at any incident power up to the damage threshold. Our structures are currently made of Si to exploit the extensive expertise in nanofabrication methods. We measure and control high-harmonics up to 8 eV photon energies. I’ll present ways that the same ideas can be applied to dielectric materials which are suitable to generate high-harmonics beyond 10 eV.\\ \\ Future work will aim at finding distinct features of phase-matching effects, which are absent in absorption-limited harmonics from homogeneous materials. Our demonstration allows brighter nanoscale solid-state high-harmonic sources, that we plan to implement for superresolution microscopy. [Preview Abstract] |
Friday, May 31, 2019 9:00AM - 9:12AM |
V03.00003: High harmonic generation (HHG) in solids. Francisco Navarrete, Marcelo Ciappina, Uwe Thumm While HHG from gaseous atoms is relatively well understood [1], catalyzed by recent experiments [2], mechanisms for and the characteristics of HHG in solids are currently debated [3-6]. We will discuss our analysis of intra- and inter-band HHG for crystalline model solids based on a single-active-electron numerical model. For ZnO and MgO crystals these simulations show that initial states over an extended crystal-momentum interval around the $\Gamma $ point contribute noticeably to the HH yield. The extent of this interval depends on the driving-field intensity and can be determined analytically. The comparison of even and odd HHG as a function of the crystal momentum and driving-field intensity allows us to characterize calculated HHG spectra with the help of simplified analytical expressions [6]. [1] Plaja and L. Roso-Franco, Phys. Rev. B 45, 8334 (1992). [3] Le, et al., Phys. Rev. A 80, 013401 (2009). [2] Ghimire et al., Nat. Phys. 7, 138 (2011). [4] Wu, et al., Phys. Rev. A 91, 043839 (2015). [5] Vampa, et al., Phys. Rev. Lett. 113, 073901 (2014). [6] In preparation of publication. [Preview Abstract] |
Friday, May 31, 2019 9:12AM - 9:24AM |
V03.00004: Role of Symmetry Properties in Polarization of High-order Harmonics in ZnO Shima Gholam-Mirzaei, Shicheng Jiang, Erin Crites, John E. Beetar, Mamta Singh, C. D. Lin, Michael Chini Polarization-resolved measurements of high-order harmonic generation (HHG) from solids have been used to study the role of inversion symmetry in determining the harmonic spectrum. Here, we study the orientation dependent parallel- and perpendicularly-polarized HHG from ZnO. We found experimentally that the polarization states of all odd harmonics and all even harmonics depend on the crystal orientation in the same way, but that odd and even harmonics behave differently from one another. More specifically, for laser polarization parallel to the mirror plane, no perpendicular even and odd harmonics are emitted, and for the laser polarization perpendicular to the mirror plane, parallel even harmonics and perpendicular odd harmonics disappear. We further determine the ellipticity of emitted harmonics and identify features in the orientation-dependent harmonic spectrum which arise due to birefringence in the bulk crystal. Contrary to prior studies, we conclude that the universal polarization behavior observed in solid-state HHG is dictated largely by symmetry properties of the target. [Preview Abstract] |
Friday, May 31, 2019 9:24AM - 9:36AM |
V03.00005: Theoretical investigation of spatial and temporal properties of HHG in solids Lun Yue, Christopher Abadie, Mengxi Wu, Mette Gaarde High-order harmonic generation (HHG) in solids has attracted extensive interest in recent years, partly due to its potential as an avenue towards bright and compact extreme ultraviolet radiation. We present a theoretical study of the spatio-temporal properties of the harmonic radiation from a model solid interacting with a focused laser beam. We show in particular that the contributions from the interband and the intraband currents have different spatiotemporal properties. We also explore the consequences of starting from a full valence band, as opposed to a single (Gamma) point in the Brillouin zone, and the influence of dephasing and decay on the harmonic radiation. Finally, we discuss the advantages and drawbacks of the different theoretical methods that exists today for investigation of HHG in solids, ranging from the numerical solution of the time-dependent Schroedinger equation to semiconductor Bloch equations. [Preview Abstract] |
Friday, May 31, 2019 9:36AM - 9:48AM |
V03.00006: High-order harmonic generation in doped and imperfect band-gap materials Lars Bojer Madsen, Chuan Yu, Kenneth Hansen We predict by time-dependent density functional theory simulations and rationalize by a three-step model of high-order harmonic generation (HHG) that a donor-doped band-gap material can enhance the overall HHG efficiency by several orders of magnitude, compared with undoped and acceptor-doped materials. This enhancement originates from the highest-occupied impurity state which has an isolated energy located within the band gap. The donor-type doping results in a harmonic cutoff different from that in the undoped and acceptor-doped cases, explained by semiclassical analysis for the impurity-state HHG. In the case of an imperfect crystal, we find that disordered systems emit suppressed harmonics in the first plateau region and enhanced harmonics in the second plateau region. The suppression of harmonics in the first plateau becomes less pronounced when introducing a lower level of disorder, while the enhancement in the second plateau region seems insensitive to the level of disorder. The universality of our findings is demonstrated for many disordered sample systems and for different laser field strengths. In addition, a time-frequency profile of HHG spectra shows that the emission of harmonics is less regular in time domain for a disordered system. [Preview Abstract] |
Friday, May 31, 2019 9:48AM - 10:00AM |
V03.00007: Topological effects in high-harmonic generation by planar sheets Helena Drueeke, Dieter Bauer Previous studies [1,2] have found interesting topological effects in the high-harmonic generation (HHG) spectra of finite, one-dimensional, periodic structures. This research expands upon these results by investigating a two-dimensional system with topological edge states. Calculations were performed with a self-consistent time-dependent density functional theory (TDDFT) approach. [1] Dieter Bauer and Kenneth K. Hansen, \emph{High-harmonic generation in solids with and without topological edge states}, Phys. Rev. Lett. 120, 177401 (2018) [2] Helena Dr\"ueke and Dieter Bauer, \emph{Robustness of topologically sensitive harmonic generation in laser-driven linear chains}, arXiv:1901.01437 [Preview Abstract] |
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