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M C E Galbraith, S Scheit, N V Golubev, G Reitsma, N Zhavoronkov, V Despré, F Lépine, A I Kuleff, M J J Vrakking, O Kornilov, H Köppel, J Mikosch
Observing the crucial first few femtoseconds of photochemical reactions requires tools typically not available in the femtochemistry toolkit. Such dynamics are now within reach with the instruments provided by attosecond science. Here, we apply experimental and theoretical methods to assess the ultrafast nonadiabatic vibronic processes in a prototypical complex system-the excited benzene cation. We use few-femtosecond duration extreme ultraviolet and visible/near-infrared laser pulses to prepare and probe excited cationic states and observe two relaxation timescales of 11 ± 3 fs and 110 ± 20 fs...
October 18, 2017: Nature Communications
Xin Tang, Shujing Chen, Chengyou Lin, Yingchun Ding
In this paper, we present a design method of broadband reflective circular polarizer (BRCP) in the extreme ultraviolet (EUV) region. By using this method, we designed three BRCPs with a 6, 12 and 18 eV bandwidth, respectively. Then, we investigated the performances of designed BRCPs in theory. The results indicated that the reflected lights of these BRCPs all showed a nearly 100% circular polarization degree and considerable circular reflection in their design band. In addition, we also studied the origin of high circular polarization degree by analyzing the phase shift and the reflectivity ratio between s- and p-polarized lights induced by the reflection of BRCPs...
September 18, 2017: Optics Express
Han-Zhen Li, Tong-Pu Yu, Li-Xiang Hu, Yan Yin, De-Bin Zou, Jian-Xun Liu, Wei-Quan Wang, Shun Hu, Fu-Qiu Shao
We propose a novel scheme to generate ultra-bright ultra-short γ-ray flashes and high-energy-density attosecond positron bunches by using multi-dimensional particle-in-cell simulations with quantum electrodynamics effects incorporated. By irradiating a 10 PW laser pulse with an intensity of 10(23) W/cm(2) onto a micro-wire target, surface electrons are dragged-out of the micro-wire and are effectively accelerated to several GeV energies by the laser ponderomotive force, forming relativistic attosecond electron bunches...
September 4, 2017: Optics Express
Jin-Bin Li, Xiao Zhang, Sheng-Jun Yue, Hong-Mei Wu, Bi-Tao Hu, Hong-Chuan Du
We theoretically investigate high-order harmonic generation (HHG) from solids in two-color fields. It is found that under the premise of maintaining the same amplitude, the intensity of the second plateau can be enhanced by two to three orders in a proper two-color field compared with the result in the monochromatic field with the same frequency as the driving pulse of the two-color field. This can be attributed to the fact that most excited electrons can be driven to the top of the first conduction band due to the larger vector potential of the two-color fields, which leads to the higher electron population of upper conduction bands...
August 7, 2017: Optics Express
Jie Li, Xiaoming Ren, Yanchun Yin, Kun Zhao, Andrew Chew, Yan Cheng, Eric Cunningham, Yang Wang, Shuyuan Hu, Yi Wu, Michael Chini, Zenghu Chang
Nature Communications 8:186 doi: 10.1038/s41467-017-00321-0 (2017); Article published online: 4 August 2017.
October 2, 2017: Nature Communications
Nicolas Tancogne-Dejean, Oliver D Mücke, Franz X Kärtner, Angel Rubio
The strong ellipticity dependence of high-harmonic generation (HHG) in gases enables numerous experimental techniques that are nowadays routinely used, for instance, to create isolated attosecond pulses. Extending such techniques to solids requires a fundamental understanding of the microscopic mechanism of HHG. Here we use first-principles simulations within a time-dependent density-functional framework and show how intraband and interband mechanisms are strongly and differently affected by the ellipticity of the driving laser field...
September 29, 2017: Nature Communications
Yong Sing You, Yanchun Yin, Yi Wu, Andrew Chew, Xiaoming Ren, Fengjiang Zhuang, Shima Gholam-Mirzaei, Michael Chini, Zenghu Chang, Shambhu Ghimire
High-harmonic generation in isolated atoms and molecules has been widely utilized in extreme ultraviolet photonics and attosecond pulse metrology. Recently, high-harmonic generation has been observed in solids, which could lead to important applications such as all-optical methods to image valance charge density and reconstruct electronic band structures, as well as compact extreme ultraviolet light sources. So far these studies are confined to crystalline solids; therefore, decoupling the respective roles of long-range periodicity and high density has been challenging...
September 28, 2017: Nature Communications
Federico J Furch, Tobias Witting, Achut Giree, Chao Luan, Felix Schell, Gunnar Arisholm, Claus P Schulz, Marc J J Vrakking
Noncollinear optical parametric amplifiers (NOPAs) have become the leading technique for the amplification of carrier-envelope phase (CEP)-stable, few-cycle pulses at high repetition rate and high average power. In this Letter, a NOPA operating at a repetition rate of 100 kHz delivering more than 24 W of average power before compression is reported. The amplified bandwidth supports sub-7 fs pulse durations and pulse compression close to the transform limit is realized. CEP stability after amplification is demonstrated...
July 1, 2017: Optics Letters
Joshua W Hollett, Wen Li
The relative momentum of electron pairs in atoms and small molecules is examined through calculation of the p1 · p2 probability distribution. The likelihood of aligned or antialigned momenta between paired electrons is determined from the calculated distributions. Coulomb correlation aligns the momenta of electron pairs, and the amount of alignment varies when considering momenta in specific directions in three-dimensional space. A static electric field is found to have competing effects on momentum alignment parallel and perpendicular to the electric field...
October 9, 2017: Journal of Physical Chemistry. A
Takuya Higuchi, Christian Heide, Konrad Ullmann, Heiko B Weber, Peter Hommelhoff
The ability to steer electrons using the strong electromagnetic field of light has opened up the possibility of controlling electron dynamics on the sub-femtosecond (less than 10(-15) seconds) timescale. In dielectrics and semiconductors, various light-field-driven effects have been explored, including high-harmonic generation, sub-optical-cycle interband population transfer and the non-perturbative change of the transient polarizability. In contrast, much less is known about light-field-driven electron dynamics in narrow-bandgap systems or in conductors, in which screening due to free carriers or light absorption hinders the application of strong optical fields...
October 12, 2017: Nature
L Ortmann, J A Pérez-Hernández, M F Ciappina, J Schötz, A Chacón, G Zeraouli, M F Kling, L Roso, M Lewenstein, A S Landsman
Studies of strong field ionization have historically relied on the strong field approximation, which neglects all spatial dependence in the forces experienced by the electron after ionization. More recently, the small spatial inhomogeneity introduced by the long-range Coulomb potential has been linked to a number of important features in the photoelectron spectrum, such as Coulomb asymmetry, Coulomb focusing, and the low energy structure. Here, we demonstrate using midinfrared laser wavelength that a time-varying spatial dependence in the laser electric field, such as that produced in the vicinity of a nanostructure, creates a prominent higher energy peak...
August 4, 2017: Physical Review Letters
Kevin M Dorney, Jennifer L Ellis, Carlos Hernández-García, Daniel D Hickstein, Christopher A Mancuso, Nathan Brooks, Tingting Fan, Guangyu Fan, Dmitriy Zusin, Christian Gentry, Patrik Grychtol, Henry C Kapteyn, Margaret M Murnane
High harmonics driven by two-color counterrotating circularly polarized laser fields are a unique source of bright, circularly polarized, extreme ultraviolet, and soft x-ray beams, where the individual harmonics themselves are completely circularly polarized. Here, we demonstrate the ability to preferentially select either the right or left circularly polarized harmonics simply by adjusting the relative intensity ratio of the bichromatic circularly polarized driving laser field. In the frequency domain, this significantly enhances the harmonic orders that rotate in the same direction as the higher-intensity driving laser...
August 11, 2017: Physical Review Letters
Fabian Siek, Sergej Neb, Peter Bartz, Matthias Hensen, Christian Strüber, Sebastian Fiechter, Miquel Torrent-Sucarrat, Vyacheslav M Silkin, Eugene E Krasovskii, Nikolay M Kabachnik, Stephan Fritzsche, Ricardo Díez Muiño, Pedro M Echenique, Andrey K Kazansky, Norbert Müller, Walter Pfeiffer, Ulrich Heinzmann
Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe2) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe2, the photoemission events are time ordered with rising initial-state angular momentum...
September 22, 2017: Science
Kai-Jun Yuan, André D Bandrauk
Exploring ultrafast charge migration is of great importance in biological and chemical reactions. We present a scheme to monitor attosecond charge migration in molecules by electron diffraction with spatial and temporal resolutions from ab initio numerical simulations. An ultraviolet pulse creates a coherent superposition of electronic states, after which a time-delayed attosecond X-ray pulse is used to ionize the molecule. It is found that diffraction patterns in the X-ray photoelectron spectra show an asymmetric structure, which is dependent on the time delay between the pump-probe pulses, encoding the information of molecular orbital symmetry and chemical bonding...
October 4, 2017: Physical Chemistry Chemical Physics: PCCP
A Moulet, J B Bertrand, T Klostermann, A Guggenmos, N Karpowicz, E Goulielmakis
The dynamic response of excitons in solids is central to modern condensed-phase physics, material sciences, and photonic technologies. However, study and control have hitherto been limited to photon energies lower than the fundamental band gap. Here we report application of attosecond soft x-ray and attosecond optical pulses to study the dynamics of core-excitons at the L2,3 edge of Si in silicon dioxide (SiO2). This attosecond x-ray absorption near-edge spectroscopy (AXANES) technique enables direct probing of the excitons' quasiparticle character, tracking of their subfemtosecond relaxation, the measurement of excitonic polarizability, and observation of dark core-excitonic states...
September 15, 2017: Science
Daniela Rupp, Nils Monserud, Bruno Langbehn, Mario Sauppe, Julian Zimmermann, Yevheniy Ovcharenko, Thomas Möller, Fabio Frassetto, Luca Poletto, Andrea Trabattoni, Francesca Calegari, Mauro Nisoli, Katharina Sander, Christian Peltz, Marc J Vrakking, Thomas Fennel, Arnaud Rouzée
Coherent diffractive imaging of individual free nanoparticles has opened routes for the in situ analysis of their transient structural, optical, and electronic properties. So far, single-shot single-particle diffraction was assumed to be feasible only at extreme ultraviolet and X-ray free-electron lasers, restricting this research field to large-scale facilities. Here we demonstrate single-shot imaging of isolated helium nanodroplets using extreme ultraviolet pulses from a femtosecond-laser-driven high harmonic source...
September 8, 2017: Nature Communications
Sampad Bag, Sankhabrata Chandra, Atanu Bhattacharya
Molecular attosecond science has already started contributing to our fundamental understanding of ultrafast purely electron dynamics in isolated molecules under vacuum. Extending attosecond science to the liquid phase is expected to offer new insight into the influence of a surrounding solvent environment on the attosecond electron dynamics in solvated molecules. A systematic theoretical investigation of the attochemistry of solvated molecules would help one design attosecond experiments under ambient conditions to explore the attochemistry in a liquid environment...
October 11, 2017: Physical Chemistry Chemical Physics: PCCP
J Schmidt, A Guggenmos, S H Chew, A Gliserin, M Högner, M F Kling, J Zou, C Späth, U Kleineberg
We present a newly developed high harmonic beamline for time-, angle-, and carrier-envelope phase-resolved extreme ultraviolet photoemission spectroscopy on solid targets for the investigation of ultrafast band structure dynamics in the low-fs to sub-fs time regime. The source operates at a repetition rate of 10 kHz and is driven by 5 fs few-cycle near-infrared laser pulses generating high harmonic radiation with photon energies up to 120 eV at a feasible flux. The experimental end station consists of a complementary combination of photoelectron detectors which are able to spectroscopically address electron dynamics both in real and in k-space...
August 2017: Review of Scientific Instruments
Rundong Zhao, Yanoar Pribadi Sarwono, Rui-Qin Zhang
The tunneling lifetime of an electron escaping from an atom is calculated using a projected Green's function method, combining with the radial potential of the atom which is obtained from density functional theory. Results of the calculated electron tunneling lifetimes in model systems such as a quantum dot are shown to be comparable with other theoretical studies. For the first time, we have obtained the tunneling lifetimes of electrons escaping from a series of atoms (He, Ne, Ar, Kr, H, Li, Na, K) under a static electric field...
August 14, 2017: Journal of Chemical Physics
Jakob Petersen, Eli Pollak
Attosecond ionization experiments have not resolved the question "What is the tunneling time?". Different definitions of tunneling time lead to different results. Second, a zero tunneling time for a material particle suggests that the nonrelativistic theory includes speeds greater than the speed of light. Chemical reactions, occurring via tunneling, should then not be considered in terms of a nonrelativistic quantum theory calling into question quantum dynamics computations on tunneling reactions. To answer these questions, we define a new experimentally measurable paradigm, the tunneling flight time, and show that it vanishes for scattering through an Eckart or a square barrier, irrespective of barrier length or height, generalizing the Hartman effect...
August 15, 2017: Journal of Physical Chemistry Letters
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