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N Lilienfein, C Hofer, S Holzberger, C Matzer, P Zimmermann, M Trubetskov, V Pervak, I Pupeza
We address the challenge of increasing the bandwidth of high-finesse femtosecond enhancement cavities and demonstrate a broad spectrum spanning 1800  cm<sup>-1</sup> (195 nm) at -10  dB around a central wavelength of 1050 nm in an EC with an average finesse exceeding 300. This will benefit a host of spectroscopic applications, including transient absorption spectroscopy, direct frequency comb spectroscopy, and Raman spectroscopy. The pulse circulating in the EC is composed of only 5.4 optical cycles, at a kilowatt-level average power...
January 15, 2017: Optics Letters
Marcelo F Ciappina, J Perez-Hernandez, Alexandra Landsman, William Okell, Sergey Zherebtsov, Benjamin Förg, Johannes Schötz, Lennart Seiffert, Thomas Fennel, Tahir Shaaran, Tomas Zimmermann, Alexis Chacón, Roland Guichard, Amelle Zair, John Tisch, J Marangos, Tobias Witting, Avi Braun, Stefan Maier, Luis Roso, Michael Krüger, Peter Hommelhoff, Matthias Kling, Ferenc Krausz, Maciej Lewenstein
Recently two emerging areas of research, attosecond and nanoscale physics, have started to come together. Attosecond physics deals with phenomena occurring when ultrashort laser pulses, with duration on the femto- and sub-femtosecond time scales, interact with atoms, molecules or solids. The laser-induced electron dynamics occurs natively on a timescale down to a few hundred or even tens of attoseconds, which is comparable with the optical field. For comparison, the revolution of an electron on a 1s orbital of a hydrogen atom is 152 as...
January 6, 2017: Reports on Progress in Physics
Carlos Marante, Markus Klinker, Inés Corral, Jesús González-Vázquez, Luca Argenti, Fernando Martín
The theoretical description of observables in attosecond pump-probe experiments requires a good representation of the system's ionization continuum. For polyelectronic molecules, however, this is still a challenge, due to the complicated short-range structure of correlated electronic wave functions. Whereas quantum chemistry packages (QCP) implementing sophisticated methods to compute bound electronic molecular states are well-established, comparable tools for the continuum are not widely available yet. To tackle this problem, we have developed a new approach that, by means of a hybrid Gaussian-B-spline basis, interfaces existing QCPs with close-coupling scattering methods...
January 6, 2017: Journal of Chemical Theory and Computation
Sankhabrata Chandra, Atanu Bhattacharya
In general, charge migration can occur via pure electron-electron correlation and relaxation or via coupling with nuclear motion. We must understand both aspects of charge migration through the non-hydrogen noncovalent bonds to harness full potential of the halogen-, chalcogen-, pnicogen- and tetrel-bonded photosensitive functional materials. This feature article, however, is focused on the pure relaxation- and correlation-driven charge migration, subsequent charge localization, and finally on charge-directed reactivity in the non-hydrogen noncovalent bonded clusters...
December 29, 2016: Journal of Physical Chemistry. A
E W Larsen, S Carlström, E Lorek, C M Heyl, D Paleček, K J Schafer, A L'Huillier, D Zigmantas, J Mauritsson
The sub-cycle dynamics of electrons driven by strong laser fields is central to the emerging field of attosecond science. We demonstrate how the dynamics can be probed through high-order harmonic generation, where different trajectories leading to the same harmonic order are initiated at different times, thereby probing different field strengths. We find large differences between the trajectories with respect to both their sensitivity to driving field ellipticity and resonant enhancement. To accurately describe the ellipticity dependence of the long trajectory harmonics we must include a sub-cycle change of the initial velocity distribution of the electron and its excursion time...
December 19, 2016: Scientific Reports
L Cattaneo, J Vos, M Lucchini, L Gallmann, C Cirelli, U Keller
Recent progress in the generation of ultra-short laser pulses has enabled the measurement of photoionization time delays with attosecond precision. For single photoemission time delays the most common techniques are based on attosecond streaking and the reconstruction of attosecond beating by interference of two-photon transitions (RABBITT). These are pump-probe techniques employing an extreme-ultraviolet (XUV) single attosecond pump pulse for streaking or an attosecond pump pulse train for RABBITT, and a phase-locked infrared (IR) probe pulse...
December 12, 2016: Optics Express
Cheng Jin, Kyung-Han Hong, C D Lin
We numerically demonstrate the generation of intense, low-divergence soft X-ray isolated attosecond pulses in a gas-filled hollow waveguide using synthesized few-cycle two-color laser waveforms. The waveform is a superposition of a fundamental and its second harmonic optimized such that highest harmonic yields are emitted from each atom. We then optimize the gas pressure and the length and radius of the waveguide such that bright coherent high-order harmonics with angular divergence smaller than 1 mrad are generated, for photon energy from the extreme ultraviolet to soft X-rays...
December 8, 2016: Scientific Reports
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
No abstract text is available yet for this article.
December 16, 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...
December 16, 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
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