Bulletin of the American Physical Society
47th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 61, Number 8
Monday–Friday, May 23–27, 2016; Providence, Rhode Island
Session P7: Novel Light Sources and Imaging Techniques |
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Chair: Thomas Allison, Stony Brook University Room: 553AB |
Thursday, May 26, 2016 2:00PM - 2:12PM |
P7.00001: X-ray holography in-flight Tais Gorkhover, Anatoli Ulmer, Ken Ferguson, Max Bucher, Tomas Ekeberg, Max Hantke, Benedikt Daurer, Carl Nettelblad, Johan Bielecki, Guila Faigel, Dirk Hasse, Andrew Morgan, Kerstin Mühlig, Marvin Seibert, Henry Chapman, Janos Hajdu, Filipe Maia, Thomas Moeller, Christoph Bostedt The advent of X-ray free-electron lasers, delivering ultra intense femtosecond X-ray flashes, opens the door for structure determination of single nanoparticles and biosamples with single shots. The first X-ray diffraction imaging experiments at LCLS delivered promising results on samples in the gas phase. However, the reconstruction of non-periodic structures is still challenging due to the loss of phase information. Meanwhile, X-ray holographic approaches allow for recording the phase directly into the diffraction image. In my talk, I will present the first successful proof-of-principle experiment for ``in-flight''-holography with free viruses.~Our experiments pave the way for unique studies on levitating~nanospecimen that are of central interest in several scientific communities including atmosphere research, chemistry, material sciences, and studies on matter under extreme conditions. [Preview Abstract] |
Thursday, May 26, 2016 2:12PM - 2:24PM |
P7.00002: Imaging plasmonic fields near gold nanospheres in attosecond time-resolved streaked photoelectron spectra Jianxiong Li, Uwe Thumm To study time-resolved photoemission from gold nanospheres, we introduce a quantum-mechanical approach, including the plasmonic near-field-enhancement of the streaking field at the surface of the nanosphere. We use Mie theory to calculate the plasmonically enhanced fields near 10 to 200 nm gold nanospheres, driven by incident near infrared (NIR) or visible laser pulses. We model the gold conduction band in terms of a spherical square well potential. Our simulated streaked photoelectron spectra reveal a plasmonic amplitude enhancement and phase shift related to calculations that exclude the induced plasmonic field. The phase shift is due to the plasma resonance. This suggests the use of streaked photoelectron spectroscopy for imaging the dielectric response and plasmonic field near nanoparticles. [Preview Abstract] |
Thursday, May 26, 2016 2:24PM - 2:36PM |
P7.00003: Mixed-Color Multiphoton Transitions as Additional Quantum Channels for Electron Photoemission Wayne Huang, Maria Becker, Joshua Beck, Herman Batelaan We demonstrate mixed-color electron photoemission from tungsten nanotips. In the experiment, second-harmonic photons were introduced to modify the multiphoton emission process. A twofold increase in quantum efficiency results from the opening up of an additional three-photon quantum channel. The super-additive photoelectron signal can be controlled by input power, field polarization, and pulse overlap. The results of our study provide new prospects for quantum photonics, multiphoton microscopy, and spin-polarized electron sources.\\ We acknowledge supports from NSF, Grant Number 1306565, 1430519. [Preview Abstract] |
Thursday, May 26, 2016 2:36PM - 2:48PM |
P7.00004: Imaging population transfer in atoms with ultrafast electron pulses Hua-Chieh Shao, Anthony F. Starace Ultrafast electron diffraction and microscopy have made significant progress recently in investigating atomic-scale structural dynamics in gas-phase and condensed materials. With these advances, direct imaging of electronic motions in atoms and molecules by ultrafast electron diffraction is anticipated. We propose imaging a laser-driven coherent population transfer in lithium atoms by femtosecond ultrafast electron pulses. Valuable information and insight can be obtained from studying such a system in order to refine ultrafast electron techniques and to interpret experimental results. Adiabatic passage by level crossing is used to transfer the electron population from the $2s$ to the $2p$ state. Our simulations demonstrate the ability of ultrafast electron diffraction to image this population transfer, as the time-dependent diffraction images reflect the electronic motion in the scattering intensity and angular distribution. Furthermore, asymmetric diffraction patterns indicate that even the relative phases of the electronic wave function can be resolved, provided there is sufficient temporal resolution. [Preview Abstract] |
Thursday, May 26, 2016 2:48PM - 3:00PM |
P7.00005: Coherence effects in the ultra-intense laser-induced ultrafast response of complex atoms Yongqiang Li, Jianmin Yuan Both coherent pumping and energy relaxation play important roles in understanding physical processes of ultra-intense coherent light-matter interactions. Here, using a large-scale quantum master equation approach, we describe dynamical processes of practical open quantum systems driven by both coherent and stochastic interactions. As examples, two typical cases of light-matter interactions are studied. First, we investigate coherent dynamics of inner-shell electrons of a neon gas irradiated by a high intensity X-ray laser along with vast number of decaying channels. In these single-photon dominated processes, we find that, due to coherence-induced Rabi oscillations and power broadening effects, the photon absorptions of a neon gas can be suppressed resulting in differences in ionization processes and final ion-stage distributions. Second, we take helium as an example of multi-photon and multichannel interference dominated electron dynamics, by investigating the transient absorption of an isolated atto-second pulse in the presence of a femto-second infrared laser pulse.. [Preview Abstract] |
Thursday, May 26, 2016 3:00PM - 3:12PM |
P7.00006: Simulation for radiative transfer of ultra-intense x-ray pulses through a solid-density aluminum plasma Cheng Gao, Jiaolong Zeng, Jianmin Yuan Radiative transfer of ultra-intense x-ray pulses through a 1 um thick solid-density aluminium sample is investigated theoretically by solving a one-dimensional radiative transfer equation. The populations of quantum states are obtained by solving a time-dependent rate equation based on collisional-radiative approximation, which are used to determine the absorption and emission coefficients of the aluminium sample.T ransmission of the ultra-intense x-ray pulses as a function of photon energy is calculated and compared with a recent experiment, where good agreement is found and saturable absorption is evidently observed. [Preview Abstract] |
Thursday, May 26, 2016 3:12PM - 3:24PM |
P7.00007: High harmonics from solids probe Angstrom scale structure Yong Sing You, David Reis, Shambhu Ghimire The basic microscopic mechanism for the high harmonics generation (HHG) in isolated atoms and molecules has been understood in the 90's. Since then the gas harmonics have been utilized widely in ultrafast x-ray science, from attosecond pulse generation to imaging molecular orbitals of the target molecule [1]. In contrast, the solid-state harmonic generation mechanism is currently being investigated [2,3,4,5,6] following the recent experimental discovery in zinc oxide crystal [7]. In particular, because of the fundamental differences, attributed to the high density and periodicity of the crystal, it was not clear if the solid-state harmonics could be used to reveal bonding structures in crystals. Here we report our experimental results on generation of XUV harmonics in single crystal MgO subjected to the field strengths on the order of 1V/{\AA} without damage. High harmonics in MgO show strong crystal orientation dependence as well as a strong laser ellipticity dependence. By exploiting these unique characteristics, we demonstrate that XUV harmonics from bulk crystals can probe Angstrom scale electronic structure of the crystal. \textbf{References} [1] Itatani, J. \textit{et al.,} Nature 432, 867--871 (2004).~ [2] Vampa, G\textit{. et al}., Phys. Rev. Lett.113, (2014) [3] Schubert O \textit{et al}., Nature Photonics 8,119-123 (2014) [4] Luu, T. T. \textit{et al}. Nature 521, 498--502 (2015). [5] Higuchi, T. \textit{et al}., Phys. Rev. Lett. 113, (2014). [6] Wu, M. \textit{et al.}, Phys. Rev. A 91, (2015). [7] Ghimire, S. \textit{et al.} \textit{Nat. Phys.} 7, 138--141 (2011). [Preview Abstract] |
Thursday, May 26, 2016 3:24PM - 3:36PM |
P7.00008: Correlated Terahertz and High Harmonic Generation from Aligned Nitrogen Molecules Yindong Huang, Chao Meng, Xiaowei Wang, Zhihui Lv, Dongwen Zhang, Wenbo Chen, Jing Zhao, Jianmin Yuan, Zengxiu Zhao When laser beams are focused on atoms and molecules, wide spectral range of photons can be radiated from the source. In the region of high energy, high harmonic generation (HHG), covering tens to hundreds electron volts, emit within the attosecond timescale. In the low energy region, terahertz wave generation (TWG) can also be generated. Synchronizing TWG with HHG is to take snapshot of the electronic dynamics with time-scale spanning over 6 orders of magnitudes. In this abstract, we report the joint measurements on TWG and HHG from pre-aligned molecules. By calibrating the angular ionization rates with the alignment dependent TWG, we reconstruct the photoionization cross section (PICS) of nitrogen in one run of experiment. The measured PICS is found to be consistent with theoretical predications, although some discrepancies exist. This all-optical method provides a new alternative for investigating molecular structures( Yindong Huang, et.al , Phys. Rev. Lett., 115, 123002, 2015). [Preview Abstract] |
Thursday, May 26, 2016 3:36PM - 3:48PM |
P7.00009: Ultrafast XUV Pulses at High Repetition Rate for Time Resolved Photoelectron Spectroscopy of Surface Dynamics Christopher Corder, Peng Zhao, Xinlong Li, Amanda R. Muraca, Matthew D. Kershis, Michael G. White, Thomas K. Allison Ultrafast photoelectron studies of surface dynamics are often limited by low repetition rates. At Stony Brook we have built a cavity-enhanced high-harmonic generation XUV source that delivers ultrafast pulses to a surface science apparatus for photoelectron spectroscopy. We begin with a Ytterbium fiber laser at a repetition rate of 78 MHz and up to 90 W of average power. After compression the pulses have $\mu$J's of energy with $<180$ fs pulse width. We then use an enhancement cavity with a finesse of a few hundred to build up to the peak intensity required for high harmonic generation. The enhancement cavity is a six mirror double folded bow-tie geometry with a focus of ~15 $\mu$m at a Krypton gas jet, followed by a Sapphire crystal at Brewster's angle for the fundamental to allow outcoupling of the harmonics. A single harmonic is selected using a time-preserving monochromator to maintain the short pulses, and is sent to an ultra high vacuum chamber with sample preparation and diagnostic tools as well as an electron energy spectrometer. This allows us to study the electronic dynamics of semiconductor surfaces and their interfaces with adsorbed molecules which enable various charge transfer effects. [Preview Abstract] |
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