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Chris J Milne, Peter M Weber, Markus Kowalewski, Jon P Marangos, Allan S Johnson, Ruaridh Forbes, Hans Jakob Wörner, Daniel Rolles, Dave Townsend, Oliver Schalk, Sebastian Mai, Morgane Vacher, R J Dwayne Miller, Martin Centurion, Ágnes Vibók, Wolfgang Domcke, Raluca Cireasa, Kiyoshi Ueda, Filippo Bencivenga, Daniel M Neumark, Albert Stolow, Artem Rudenko, Adam Kirrander, Danielle Dowek, Fernando Martín, Misha Ivanov, Jan Marcus Dahlström, Nirit Dudovich, Shaul Mukamel, Alvaro Sanchez-Gonzalez, Michael P Minitti, Dane R Austin, Victor Kimberg, Zdenek Masin
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November 30, 2016: Faraday Discussions
Sandeep Kumar, Yong Woon Parc, Alexandra S Landsman, Dong Eon Kim
Attosecond metrology using laser-based high-order harmonics has been significantly advanced and applied to various studies of electron dynamics in atoms, molecules and solids. Laser-based high-order harmonics have a limitation of low power and photon energies. There is, however, a great demand for even higher power and photon energy. Here, we propose a scheme for a terawatt attosecond (TW-as) X-ray pulse in X-ray free-electron laser controlled by a few cycle IR pulse, where one dominant current spike in an electron bunch is used repeatedly to amplify a seeded radiation to a terawatt level...
November 28, 2016: Scientific Reports
S Beaulieu, S Camp, D Descamps, A Comby, V Wanie, S Petit, F Légaré, K J Schafer, M B Gaarde, F Catoire, Y Mairesse
We investigate the role of excited states in high-order harmonic generation by studying the spectral, spatial, and temporal characteristics of the radiation produced near the ionization threshold of argon by few-cycle laser pulses. We show that the population of excited states can lead either to direct extreme ultraviolet emission through free induction decay or to the generation of high-order harmonics through ionization from these states and recombination to the ground state. By using the attosecond lighthouse technique, we demonstrate that the high-harmonic emission from excited states is temporally delayed by a few femtoseconds compared to the usual harmonics, leading to a strong nonadiabatic spectral redshift...
November 11, 2016: Physical Review Letters
Kai-Jun Yuan, André D Bandrauk
We propose a method to monitor coherent electron wave packet (CEWP) excitation dynamics with two-color attosecond laser pulses. Simulations are performed on aligned H2(+) by numerically solving the three-dimensional time-dependent Schrödinger equation with combinations of a resonant linearly polarized λl= 100/70 nm pump pulse and a circularly polarized λc=5 nm attosecond probe pulse. It is found that time dependent diffraction patterns in molecular frame photoelectron angular distributions (MFPADs) produced by the circular probe pulse exhibit sensitivity to the molecular alignments and time-dependent geometry of the CEWPs during and after the coherent excitation between the ground and excited states induced by the linear pump pulse...
November 21, 2016: Journal of Chemical Physics
Benoit Mignolet, Basile F E Curchod, Todd J Martínez
Attoscience is an emerging field where attosecond pulses or few cycle IR pulses are used to pump and probe the correlated electron-nuclear motion of molecules. We present the trajectory-guided eXternal Field Ab Initio Multiple Spawning (XFAIMS) method that models such experiments "on-the-fly," from laser pulse excitation to fragmentation or nonadiabatic relaxation to the ground electronic state. For the photoexcitation of the LiH molecule, we show that XFAIMS gives results in close agreement with numerically exact quantum dynamics simulations, both for atto- and femtosecond laser pulses...
November 21, 2016: Journal of Chemical Physics
Li-Qiang Feng, Hang Liu, Wenliang Li, Rich-Samuel Castle
Molecular high-order harmonic generation (HHG) spectra from H2(+) and its application to the generation of the isolated attosecond pulses (IAPs) have been numerically investigated. Results show that (i) the 7th harmonic order is enhanced with the nuclei around the equilibrium internuclear, and as the internuclear distance increased, this enhanced harmonic produces a red-shift (even disappearance). Theoretical analyses show that the electronic transition between the ground and the 1st excited states is responsible for the red-shift enhanced harmonic...
December 2016: Journal of Molecular Modeling
K Veyrinas, V Gruson, S J Weber, L Barreau, T Ruchon, J-F Hergott, J-C Houver, R R Lucchese, P Salières, D Dowek
Due to the intimate anisotropic interaction between an XUV light field and a molecule resulting in photoionization (PI), molecular frame photoelectron angular distributions (MFPADs) are most sensitive probes of both electronic/nuclear dynamics and the polarization state of the ionizing light field. Consequently, they encode the complex dipole matrix elements describing the dynamics of the PI transition, as well as the three normalized Stokes parameters s1, s2, s3 characterizing the complete polarization state of the light, operating as molecular polarimetry...
November 17, 2016: Faraday Discussions
Nobuyuki Takei, Christian Sommer, Claudiu Genes, Guido Pupillo, Haruka Goto, Kuniaki Koyasu, Hisashi Chiba, Matthias Weidemüller, Kenji Ohmori
Many-body correlations govern a variety of important quantum phenomena such as the emergence of superconductivity and magnetism. Understanding quantum many-body systems is thus one of the central goals of modern sciences. Here we demonstrate an experimental approach towards this goal by utilizing an ultracold Rydberg gas generated with a broadband picosecond laser pulse. We follow the ultrafast evolution of its electronic coherence by time-domain Ramsey interferometry with attosecond precision. The observed electronic coherence shows an ultrafast oscillation with a period of 1 femtosecond, whose phase shift on the attosecond timescale is consistent with many-body correlations among Rydberg atoms beyond mean-field approximations...
November 16, 2016: Nature Communications
V Gruson, L Barreau, Á Jiménez-Galan, F Risoud, J Caillat, A Maquet, B Carré, F Lepetit, J-F Hergott, T Ruchon, L Argenti, R Taïeb, F Martín, P Salières
The dynamics of quantum systems are encoded in the amplitude and phase of wave packets. However, the rapidity of electron dynamics on the attosecond scale has precluded the complete characterization of electron wave packets in the time domain. Using spectrally resolved electron interferometry, we were able to measure the amplitude and phase of a photoelectron wave packet created through a Fano autoionizing resonance in helium. In our setup, replicas obtained by two-photon transitions interfere with reference wave packets that are formed through smooth continua, allowing the full temporal reconstruction, purely from experimental data, of the resonant wave packet released in the continuum...
November 11, 2016: Science
Sha Li, R R Jones
Electrons ejected from atoms and subsequently driven to high energies in strong laser fields enable techniques from attosecond pulse generation to imaging with rescattered electrons. Analogous processes govern strong-field electron emission from nanostructures, where long wavelength radiation and large local field enhancements hold the promise for producing electrons with substantially higher energies, allowing for higher resolution time-resolved imaging. Here we report on the use of single-cycle terahertz pulses to drive electron emission from unbiased nano-tips...
November 10, 2016: Nature Communications
G Ernotte, P Lassonde, F Légaré, B E Schmidt
Generating mid infrared (MIR) pulses by difference frequency generation (DFG) is often a trade-off between the maximum stability given by all-inline intra-pulse arrangements and the independent control of pulse parameters with inter-pulse pump-probe like scenarios. We propose a coalescence between both opposing approaches by realizing an all-inline inter-pulse DFG scheme employing a 4-f setup. This allows independent manipulation of the amplitude, delay and polarization of the two corresponding spectral side bands of a supercontinuum source while maintaining 20 attoseconds jitter without any feedback stabilization...
October 17, 2016: Optics Express
Yang Li, Yueming Zhou, Mingrui He, Min Li, Peixiang Lu
Backscattering photoelectron hologram (BPH) originating from direct and backward-rescattering electrons encodes important structural information and ultrafast dynamics of the underlying processes. However, the BPH is usually overshadowed by other interference structures in the photoelectrons momentum spectra, preventing a direct extraction of information using BPH. Here we theoretically demonstrate disentanglement of the BPH from other types of interference with the orthogonal two-color field, where a weak orthogonal component is used to streak the BPH...
October 17, 2016: Optics Express
Piero Decleva, Nicola Quadri, Aurelie Perveaux, David Lauvergnat, Fabien Gatti, Benjamin Lasorne, Gábor J Halász, Ágnes Vibók
Recently we reported a series of numerical simulations proving that it is possible in principle to create an electronic wave packet and subsequent electronic motion in a neutral molecule photoexcited by a UV pump pulse within a few femtoseconds. We considered the ozone molecule: for this system the electronic wave packet leads to a dissociation process. In the present work, we investigate more specifically the time-resolved photoelectron angular distribution of the ozone molecule that provides a much more detailed description of the evolution of the electronic wave packet...
November 7, 2016: Scientific Reports
Takashi Tanaka, Yong Woon Parc, Yuichiro Kida, Ryota Kinjo, Chi Hyun Shim, In Soo Ko, Byunghoon Kim, Dong Eon Kim, Eduard Prat
A method is proposed to generate an isolated attosecond X-ray pulse in free-electron lasers, using irregularly spaced current peaks induced in an electron beam through interaction with an intense short-pulse optical laser. In comparison with a similar scheme proposed in a previous paper, the irregular arrangement of current peaks significantly improves the contrast between the main and satellite pulses, enhances the attainable peak power and simplifies the accelerator layout. Three different methods are proposed for this purpose and achievable performances are computed under realistic conditions...
November 1, 2016: Journal of Synchrotron Radiation
Hirofumi Yanagisawa, Sascha Schnepp, Christian Hafner, Matthias Hengsberger, Dong Eon Kim, Matthias F Kling, Alexandra Landsman, Lukas Gallmann, Jürg Osterwalder
Illuminating a nano-sized metallic tip with ultrashort laser pulses leads to the emission of electrons due to multiphoton excitations. As optical fields become stronger, tunnelling emission directly from the Fermi level becomes prevalent. This can generate coherent electron waves in vacuum leading to a variety of attosecond phenomena. Working at high emission currents where multi-electron effects are significant, we were able to characterize the transition from one regime to the other. Specifically, we found that the onset of laser-driven tunnelling emission is heralded by the appearance of a peculiar delayed emission channel...
October 27, 2016: Scientific Reports
M Garg, M Zhan, T T Luu, H Lakhotia, T Klostermann, A Guggenmos, E Goulielmakis
The frequency of electric currents associated with charge carriers moving in the electronic bands of solids determines the speed limit of electronics and thereby that of information and signal processing. The use of light fields to drive electrons promises access to vastly higher frequencies than conventionally used, as electric currents can be induced and manipulated on timescales faster than that of the quantum dephasing of charge carriers in solids. This forms the basis of terahertz (10(12) hertz) electronics in artificial superlattices, and has enabled light-based switches and sampling of currents extending in frequency up to a few hundred terahertz...
October 19, 2016: Nature
Nariyuki Saito, Nobuhisa Ishii, Teruto Kanai, Shuntaro Watanabe, Jiro Itatani
Long-wavelength lasers have great potential to become a new-generation drive laser for tabletop coherent light sources in the soft X-ray region. Because of the significantly low conversion efficiency from a long-wavelength light field to high-order harmonics, their pulse characterization has been carried out by measuring the carrier-envelope phase and/or spatial dependences of high harmonic spectra. However, these photon detection schemes, in general, have difficulty in obtaining information on the spectral phases, which is crucial to determine the temporal structures of high-order harmonics...
October 18, 2016: Scientific Reports
Ke Hu, Hui-Chun Wu
We study x-ray production by coherent nonlinear Thomson scattering of few-cycle laser pulses from relativistic electron sheets. For an electron sheet thicker than the wavelength of the x-ray, the scattering efficiency is found to increase by two orders of magnitude for single-cycle laser pulses, as compared with longer pulses. This enhancement is attributed to the suppression of the destructive interference during the scattering process, as well as the frequency downshift related to the ultrabroad spectra of single-cycle pulses...
October 1, 2016: Optics Letters
Anatoli S Kheifets, Alexander W Bray, Igor Bray
We study the time delay in the primary photoemission channel near the opening of an additional channel and compare it with the Wigner time delay in elastic scattering of the photoelectron near the corresponding inelastic threshold. The photoemission time delay near threshold is significantly enhanced, to a measurable 40 as, in comparison to the corresponding elastic scattering delay. The enhancement is due to the different lowest order of interelectron interaction coupling the primary and additional photoemission channels...
September 30, 2016: Physical Review Letters
Barry D Bruner, Zdeněk Mašín, Matteo Negro, Felipe Morales, Danilo Brambila, Michele Devetta, Davide Faccialà, Alex G Harvey, Misha Ivanov, Yann Mairesse, Serguei Patchkovskii, Valeria Serbinenko, Hadas Soifer, Salvatore Stagira, Caterina Vozzi, Nirit Dudovich, Olga Smirnova
High harmonic generation (HHG) spectroscopy has opened up a new frontier in ultrafast science, where electronic dynamics can be measured on an attosecond time scale. The strong laser field that triggers the high harmonic response also opens multiple quantum pathways for multielectron dynamics in molecules, resulting in a complex process of multielectron rearrangement during ionization. Using combined experimental and theoretical approaches, we show how multi-dimensional HHG spectroscopy can be used to detect and follow electronic dynamics of core rearrangement on sub-laser cycle time scales...
September 26, 2016: Faraday Discussions
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