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M Klaiber, K Z Hatsagortsyan, J Wu, S S Luo, P Grugan, B C Walker
Recollision for a laser driven atomic system is investigated in the relativistic regime via a strong field quantum description and Monte Carlo semiclassical approach. We find the relativistic recollision energy cutoff is independent of the ponderomotive potential U_{p}, in contrast to the well-known 3.2U_{p} scaling. The relativistic recollision energy cutoff is determined by the ionization potential of the atomic system and achievable with non-negligible recollision flux before entering a "rescattering free" interaction...
March 3, 2017: Physical Review Letters
Nils Raabe, Tianli Feng, Mark Mero, Haochen Tian, Youjian Song, Wolfgang Hänsel, Ronald Holzwarth, Alexander Sell, Armin Zach, Günter Steinmeyer
Attosecond spectroscopy and precision frequency metrology depend on the stabilization of the carrier-envelope phase (CEP) of mode-locked lasers. Unfortunately, the phase of only a few types of lasers can be stabilized to jitters in the few-hundred millirad range. In a comparative experimental study, we analyze a femtosecond Ti:sapphire laser and three mode-locked fiber lasers. We numerically demodulate recorded time series of the free-running carrier-envelope beat note. Our analysis indicates a correlation between amplitude and frequency fluctuations at low Fourier frequencies for essentially all lasers investigated...
March 15, 2017: Optics Letters
Xiaofan Zhang, Xiaosong Zhu, Xi Liu, Dian Wang, Qingbin Zhang, Pengfei Lan, Peixiang Lu
We propose and theoretically demonstrate a method to generate attosecond XUV pulses with tunable ellipticity from aligned molecules irradiated by a bichromatic counterrotating circularly polarized (BCCP) driving laser field. By rotating the BCCP field, the attoseond XUV pulse varies from being left elliptically polarized to right elliptically polarized. The rotation of the BCCP field can be easily achieved by adjusting the relative phases between the two circularly polarized components. This scheme will benefit a broad range of applications, including the exploration of chiral-sensitive properties of the light-matter interaction and time-resolved imaging of magnetic structures...
March 15, 2017: Optics Letters
Kevin F Lee, Xiaoyan Ding, T J Hammond, M E Fermann, G Vampa, P B Corkum
High harmonic generation in solids presents the possibility for bringing attosecond techniques to semiconductors and a simple source for frequency comb spectroscopy in the vacuum ultraviolet. We generate up to the seventh harmonic of a Tm fiber laser by focusing in silicon or zinc oxide. The harmonics are strong and stable, with no indication of material damage. Calculations show the potential for generating nineteenth harmonic photons at 12 eV photons of energy.
March 15, 2017: Optics Letters
Morgane Vacher, Michael J Bearpark, Michael A Robb, João Pedro Malhado
Knowledge about the electronic motion in molecules is essential for our understanding of chemical reactions and biological processes. The advent of attosecond techniques opens up the possibility to induce electronic motion, observe it in real time, and potentially steer it. A fundamental question remains the factors influencing electronic decoherence and the role played by nuclear motion in this process. Here, we simulate the dynamics upon ionization of the polyatomic molecules paraxylene and modified bismethylene-adamantane, with a quantum mechanical treatment of both electron and nuclear dynamics using the direct dynamics variational multiconfigurational Gaussian method...
February 24, 2017: Physical Review Letters
Alex Turpin, Laura Rego, Antonio Picón, Julio San Román, Carlos Hernández-García
We investigate theoretically the generation of extreme-ultraviolet (EUV) beams carrying fractional orbital angular momentum. To this end, we drive high-order harmonic generation with infrared conical refraction (CR) beams. We show that the high-order harmonic beams emitted in the EUV/soft x-ray regime preserve the characteristic signatures of the driving beam, namely ringlike transverse intensity profile and CR-like polarization distribution. As a result, through orbital and spin angular momentum conservation, harmonic beams are emitted with fractional orbital angular momentum, and they can be synthesized into structured attosecond helical beams -or "structured attosecond light springs"- with rotating linear polarization along the azimuth...
March 10, 2017: Scientific Reports
F Schlaepfer, A Ludwig, M Lucchini, L Kasmi, M Volkov, L Gallmann, U Keller
Attosecond pump-probe measurements are typically performed by combining attosecond pulses with more intense femtosecond, phase-locked infrared (IR) pulses because of the low average photon flux of attosecond light sources based on high-harmonic generation (HHG). Furthermore, the strong absorption of materials at the extreme ultraviolet (XUV) wavelengths of the attosecond pulses typically prevents the use of transmissive optics. As a result, pump and probe beams are typically recombined geometrically with a center-hole mirror that reflects the larger IR beam and transmits the smaller XUV, which leads to an annular beam profile of the IR...
February 20, 2017: Optics Express
Roland E Mainz, Giulio Maria Rossi, Giovanni Cirmi, Yudong Yang, Oliver D Mücke, Franz X Kärtner
We introduce a simple all-inline variation of a balanced optical cross-correlator (BOC) that allows to measure the arrival time difference (ATD), over the full Nyquist bandwidth, with increased common-mode rejection and long-term stability. An FPGA-based signal processing unit allows for real-time signal normalization and enables locking to any setpoint with an unprecedented accuracy of 0.07 % within an increased ATD range of more than 400 fs, resulting in attosecond resolution locking. The setup precision is verified with an out-of-loop measurement to be less than 80 as residual jitter paving the way for highly demanding applications such as parametric waveform synthesizers...
February 20, 2017: Optics Express
Ines Corral, Jesús González-Vázquez, Fernando Martin
The theoretical description of core-hole and core-hole excited (shake-up) states resulting from the interaction of a molecule with X-ray free electron lasers, attosecond pulses and synchrotron radiation is a challenging task, as these states lie in the ionization continuum and, therefore, are subject to variational collapse. Although much effort has been devoted in the past to describe core-hole states in the Franck Condon (FC) region, very few attempts, even less for shake up states, have been reported near the dissociation threshold, where multistate degeneracy introduces additional complications...
February 27, 2017: Journal of Chemical Theory and Computation
Henry Timmers, Yuki Kobayashi, Kristina F Chang, Maurizio Reduzzi, Daniel M Neumark, Stephen R Leone
Femtosecond laser pulses lasting only a few optical periods hold the potential for probing and manipulating the electronic degrees of freedom within matter. However, the generation of high-contrast, few-cycle pulses in the high power limit still remains nontrivial. In this Letter, we present the application of ammonium dihydrogen phosphate (ADP) as an optical medium for compensating for the higher-order dispersion of a carrier-envelope stable few-cycle waveform centered at 735 nm. The ADP crystal is capable of removing the residual third-order dispersion present in the spectral phase of an input pulse, resulting in near-transform-limited 2...
February 15, 2017: Optics Letters
Huihui Wang, Sergey I Bokarev, Saadullah G Aziz, Oliver Kühn
Recent advances in attosecond physics provide access to the correlated motion of valence and core electrons on their intrinsic timescales. For valence excitations, processes related to the electron spin are usually driven by nuclear motion. For core-excited states, where the core hole has a nonzero angular momentum, spin-orbit coupling is strong enough to drive spin flips on a much shorter time scale. Here, unprecedented short spin crossover is demonstrated for L-edge (2p→3d) excited states of a prototypical Fe(II) complex...
January 13, 2017: Physical Review Letters
M Kozák, J McNeur, K J Leedle, H Deng, N Schönenberger, A Ruehl, I Hartl, J S Harris, R L Byer, P Hommelhoff
The temporal resolution of ultrafast electron diffraction and microscopy experiments is currently limited by the available experimental techniques for the generation and characterization of electron bunches with single femtosecond or attosecond durations. Here, we present proof of principle experiments of an optical gating concept for free electrons via direct time-domain visualization of the sub-optical cycle energy and transverse momentum structure imprinted on the electron beam. We demonstrate a temporal resolution of 1...
January 25, 2017: Nature Communications
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
M F Ciappina, J A Pérez-Hernández, A S Landsman, W A Okell, S Zherebtsov, B Förg, J Schötz, L Seiffert, T Fennel, T Shaaran, T Zimmermann, A Chacón, R Guichard, A Zaïr, J W G Tisch, J P Marangos, T Witting, A Braun, S A Maier, L Roso, M Krüger, P Hommelhoff, M F Kling, F Krausz, M 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 (1 attosecond  =  1 as  =  10(-18) s), 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
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