Referierte Publikationen

2012

B. Döbrich, H. Gies, N. Neitz, and F. Karbstein
Magnetically Amplified Tunneling of the Third Kind as a Probe of Minicharged Particles
Phys. Rev. Lett., 109 :131802 (September 2012)
Abstract:
We show that magnetic fields significantly enhance a new tunneling mechanism in quantum field theories with photons coupling to fermionic minicharged particles (MCPs). We propose a dedicated laboratory experiment of the light-shining-through-walls type that can explore a parameter regime comparable to and even beyond the best model-independent cosmological bounds. With present-day technology, such an experiment is particularly sensitive to MCPs with masses in and below the meV regime as suggested by new-physics extensions of the standard model.
J. Körner, C. Vorholt, H. Liebetrau, M. Kahle, D. Klöpfel, R. Seifert, J. Hein, and M.C. Kaluza
Measurement of temperature-dependent absorption and emission spectra of Yb:YAG, Yb:LuAG, and Yb:CaF_2 between 20 °C and 200 °C and predictions on their influence on laser performance
J. Opt. Soc. Am. B, 29 :2493 (September 2012)
Abstract:
Accurate values of the emission and absorption cross sections of Yb:YAG, Yb:LuAG, and Yb:CaF_2 as a function of temperature between room temperature and 200 °C are presented. For this purpose, absorption and fluorescence spectra were measured using a setup optimized to reduce the effect of radiation trapping. From these data, emission cross sections were retrieved by combining the Fuchtbauer–Ladenburg equation and the reciprocity method. Based on our measurements, simple estimations illustrate the effect of temperature shifts that are likely to occur in typical laser setups. Our results show that even minor temperature variations can have significant impact on the laser performance using Yb:YAG and Yb:LuAG as an active medium, while Yb:CaF_2 appears to be rather insensitive.
A. V. Maiorova, A. Surzhykov, S. Tashenov, V. M. Shabaev, and T. Stöhlker
Production and diagnostics of spin-polarized heavy ions in sequential two-electron radiative recombination
Phys. Rev. A, 86 :032701 (September 2012)
Abstract:
In the present work we investigate the sequential radiative recombination (RR) of initially bare ions colliding with two spatially separated electron targets. It is shown that magnetic sublevel population of the hydrogenlike ions, produced by the electron capture from the first target, depends on the emission direction of the (first) RR photon. This population, which can be expressed in terms of the polarization parameters, affects then the angular and polarization properties of the radiation emitted in the collision with the second target. The coincidence measurements of two subsequent RR photons may allow one to understand, therefore, the production and diagnostics of the ion spin polarization. In order to describe this polarization production and diagnostic scheme we derive the general expression for the γ-γ correlation function. Detailed calculations for the dependence of this function on the geometry of photon emission and collision energy are performed for the radiative recombination of bare uranium ions.
A. Paz, S. Kuschel, C. Rödel, M. Schnell, O. Jäckel, M.C. Kaluza, and G.G. Paulus
Thomson backscattering from laser-generated, relativistically moving high-density electron layers
New J. Phys., 14 :093018 (September 2012)
Abstract:
We show experimentally that extreme ultraviolet radiation is produced when a laser pulse is Thomson backscattered from sheets of relativistic electrons that are formed at the rear surface of a foil irradiated on its front side with a high-intensity laser. An all-optical setup is realized using the Jena titanium:sapphire ten-terawatt laser system with an enhanced amplified spontaneous emission background of 10^−12. The main pulse is split into two: one of them accelerates electrons from thin aluminium foil targets to energies of the order of some MeV and the other, counterpropagating probe pulse Thomson-backscatters off these electrons when they exit the target rear side. The process produced photons within a wide spectral range of some tens of eV as a result of the broad electron energy distribution. The highest scattering intensity is observed when the probe pulse arrives at the target rear surface 100 fs after irradiation of the target front side by the pump pulse, corresponding to the maximum flux of hot electrons at the interaction region. These results can provide time-resolved information about the evolution of the rear-surface electron sheath and hence about the dynamics of the electric fields responsible for the acceleration of ions from the rear surface of thin, laser-irradiated foils.
M. Vogel, W. Quint, G.G. Paulus, and T. Stöhlker
A Penning trap for advanced studies with particles in extreme laser fields
Nucl. Instr. Meth. Phys. Res. B, 285 :65 (August 2012)
Abstract:
We present a Penning trap as a tool for advanced studies of particles in extreme laser fields. Particularly, trap-specific manipulation techniques allow control over the confined particles’ localization and spatial density by use of trap electrodes as ‘electrostatic tweezers’ and by application of a ‘rotating wall’, respectively. It is thereby possible to select and prepare well-defined ion ensembles and to optimize the laser–particle interaction. Non-destructive detection of reaction educts and products with up to single-ion sensitivity supports advanced studies by maintaining the products for further studies at extended confinement times of minutes and above. The trap features endcaps with conical openings for applications with strongly focused lasers. We show that such a modification of a cylindrical trap is possible while harmonicity and tunability are maintained.
S. Keppler, M. Hornung, R. Bödefeld, M. Kahle, J. Hein, and M.C. Kaluza
All-reflective, highly accurate polarization rotator for high-power short-pulse laser systems
Opt. Express, 20 :20742 (August 2012)
Abstract:
We present the setup of a polarization rotating device and its adaption for high-power short-pulse laser systems. Compared to conventional halfwave plates, the all-reflective principle using three zero-phase shift mirrors provides a higher accuracy and a higher damage threshold. Since plan-parallel plates, e.g. these halfwave plates, generate postpulses, which could lead to the generation of prepulses during the subsequent laser chain, the presented device avoids parasitic pulses and is therefore the preferable alternative for high-contrast applications. Moreover the device is easily scalable for large beam diameters and its spectral reflectivity can be adjusted by an appropriate mirror coating to be well suited for ultra-short laser pulses.
A. Willner, A. Hage, R. Riedel, I. Grguraš, A. Simoncig, M. Schulz, T. Dzelzainis, H. Höppner, S. Huber, M. J. Prandolini, B. Dromey, M. Zepf, A. L. Cavalieri, and F. Tavella
Coherent spectral enhancement of carrier-envelope-phase stable continua with dual-gas high harmonic generation
Opt. Lett., 37 :3672 (August 2012)
Abstract:
Attosecond science is enabled by the ability to convert femtosecond near-infrared laser light into coherent harmonics in the extreme ultraviolet spectral range. While attosecond sources have been utilized in experiments that have not demanded high intensities, substantially higher photon flux would provide a natural link to the next significant experimental breakthrough. Numerical simulations of dual-gas high harmonic generation indicate that the output in the cutoff spectral region can be selectively enhanced without disturbing the single-atom gating mechanism. Here, we summarize the results of these simulations and present first experimental findings to support these predictions.
S. Fritzsche, A. Surzhykov, A. Gumberidze, and T. Stöhlker
Electron emission from highly charged ions - signatures of magnetic interactions and retardation in strong fields
New J. Phys., 14 :083018 (August 2012)
Abstract:
The electron emission of highly charged ions has been reanalyzed with the goal of separating the magnetic and retardation contributions to the electron-electron (e-e) interaction from the static Coulomb repulsion in strong fields. A remarkable change in the electron angular distribution due to the relativistic terms in the e-e interaction is found, especially for the autoionization of beryllium-like projectiles, following a 1s → 2p_(3/2) Coulomb excitation in collision with some target nuclei. For low-energetic, high-Z projectiles with Tp ≤ 10 MeV u^(−1), a diminished (electron) emission in the forward direction as well as oscillations in the electron angular distribution due to the magnetic and retarded interactions are predicted for the autoionization of the 1s 2s^(2) 2p_(3/2) 3^P_2 resonance into the 1s^2 2s^2 S_(1/2) ground and the 1s^2 2p^2P_(1/2) excited levels of the finally lithium-like ions, and in contrast to a pure Coulomb repulsion between the bound and emitted electrons. The proposed excitation-autoionization process can be observed at existing storage rings and will provide a novel insight into the dynamics of electrons in strong fields.
G. R. Plateau, C. G. R. Geddes, D. B. Thorn, M. Chen, C. Benedetti, E. Esarey, A. J. Gonsalves, N. H. Matlis, K. Nakamura, C. B. Schroeder, S. Shiraishi, T. Sokollik, J. van Tilborg, C. Toth, S. Trotsenko, T. S. Kim, M. Battaglia, T. Stöhlker, and W. P. Leemans
Low-Emittance Electron Bunches from a Laser-Plasma Accelerator Measured using Single-Shot X-Ray Spectroscopy
Phys. Rev. Lett., 109 :064802 (August 2012)
Abstract:
X-ray spectroscopy is used to obtain single-shot information on electron beam emittance in a low-energy-spread 0.5 GeV-class laser-plasma accelerator. Measurements of betatron radiation from 2 to 20 keV used a CCD and single-photon counting techniques. By matching x-ray spectra to betatron radiation models, the electron bunch radius inside the plasma is estimated to be ~0.1  μm. Combining this with simultaneous electron spectra, normalized transverse emittance is estimated to be as low as 0.1 mm mrad, consistent with three-dimensional particle-in-cell simulations. Correlations of the bunch radius with electron beam parameters are presented.
A. Gopal, T. May, S. Herzer, A. Reinhard, S. Minardi, M. Schubert, U. Dillner, B. Pradarutti, J. Polz, T. Gaumnitz, M.C. Kaluza, O. Jäckel, S. Riehemann, W. Ziegler, H.-P. Gemünd, H.-G. Meyer, and G.G. Paulus
Observation of energetic terahertz pulses from relativistic solid density plasmas
New J. Phys., 14 :083012 (August 2012)
Abstract:
We report the first experimental observation of terahertz (THz) radiation from the rear surface of a solid target while interacting with an intense laser pulse. Experimental and two-dimensional particle-in-cell simulations show that the observed THz radiation is mostly emitted at large angles to the target normal. Numerical results point out that a large part of the emission originates from a micron-scale plasma sheath at the rear surface of the target, which is also responsible for the ion acceleration. This opens a perspective for the application of THz radiation detection for on-site diagnostics of particle acceleration in laser-produced plasmas.
M. Harmand, C. D. Murphy, C. R. D. Brown, M. Cammarata, T. Döppner, S. Düsterer, D. Fritz, E. Förster, E. Galtier, J. Gaudin, S. H. Glenzer, S. Göde, G. Gregori, V. Hilbert, D. Hochhaus, T. Laarmann, H. J. Lee, H. Lemke, K. -H. Meiwes-Broer, A. Moinard, P. Neumayer, A. Przystawik, H. Redlin, M. Schulz, S. Skruszewicz, F. Tavella, T. Tschentscher, T. White, U. Zastrau, and S. Toleikis
Plasma switch as a temporal overlap tool for pump-probe experiments at FEL facilities
J. Instrum., 7 :P08007 (August 2012)
Abstract:
We have developed an easy-to-use and reliable timing tool to determine the arrival time of an optical laser and a free electron laser (FEL) pulses within the jitter limitation. This timing tool can be used from XUV to X-rays and exploits high FELs intensities. It uses a shadowgraph technique where we optically (at 800 nm) image a plasma created by an intense XUV or X-ray FEL pulse on a transparent sample (glass slide) directly placed at the pump - probe sample position. It is based on the physical principle that the optical properties of the material are drastically changed when its free electron density reaches the critical density. At this point the excited glass sample becomes opaque to the optical laser pulse. The ultra-short and intense XUV or X-ray FEL pulse ensures that a critical electron density can be reached via photoionization and subsequent collisional ionization within the XUV or X-ray FEL pulse duration or even faster. This technique allows to determine the relative arrival time between the optical laser and the FEL pulses in only few single shots with an accuracy mainly limited by the optical laser pulse duration and the jitter between the FEL and the optical laser. Considering the major interest in pump-probe experiments at FEL facilities in general, such a femtosecond resolution timing tool is of utmost importance.
B. B. Pollock, J. Meinecke, S. Kuschel, J. S. Ross, J. L. Shaw, C. Stoafer, L. Divol, G. R. Tynan, and S. H. Glenzer
Simultaneous imaging electron- and ion-feature Thomson scattering measurements of radiatively heated Xe
Rev. Sci. Instrum., 83 :10E348 (August 2012)
Abstract:
Uniform density and temperature Xe plasmas have been produced over > 4 mm scale-lengths using x-rays generated in a cylindrical Pb cavity. The cavity is 750 μm in depth and diameter, and is heated by a 300 J, 2 ns square, 1054 nm laser pulse focused to a spot size of 200 μm at the cavity entrance. The plasma is characterized by simultaneous imaging Thomson scattering measurements from both the electron and ion scattering features. The electron feature measurement determines the spatial electron density and temperature profile, and using these parameters as constraints in the ion feature analysis allows an accurate determination of the charge state of the Xe ions. The Thomson scattering probe beam is 40 J, 200 ps, and 527 nm, and is focused to a 100 μm spot size at the entrance of the Pb cavity. Each system has a spatial resolution of 25 μm, a temporal resolution of 200 ps (as determined by the probe duration), and a spectral resolution of 2 nm for the electron feature system and 0.025 nm for the ion feature system. The experiment is performed in a Xe filled target chamber at a neutral pressure of 3–10 Torr, and the x-rays produced in the Pb ionize and heat the Xe to a charge state of 20 ± 4 at up to 200 eV electron temperatures.
G. Maleshkov, P. Hansinger, N. Dimitrov, A. Dreischuh, and G. Paulus
Branching optical signals by fractional vortex dipoles
Opt. Commun., 285 :3529 (July 2012)
Abstract:
We study the evolution and interaction of semi-infinite dark beams carrying phase dislocations, where step- and screw-like phase profiles are combined. Similar to dark beams with a finite length, semi-infinite dark beams tend to move in transversal direction with respect to their background beam. In addition, they develop a snake-like instability and optical vortices detach from their bending ends. We are looking for appropriate conditions to control the process of concatenating and crossing the ends of several such semi-infinite dark beams in a way suitable for probe-beam branching and routing in self-defocusing Kerr nonlinear media. Colinear and perpendicular probe beam propagations in the optically-induced guiding structures are modeled and analyzed with respect to the branching efficiency to respective virtual output channels.
S. Zherebtsov, F. Süssmann, C. Peltz, J. Plenge, K. J. Betsch, I. Znakovskaya, A. S. Alnaser, N. G. Johnson, M. Kübel, A. Horn, V. Mondes, C. Graf, S. A. Trushin, A. Azzeer, M. J. J. Vrakking, G.G. Paulus, F. Krausz, E. Rühl, T. Fennel, and M. F. Kling
Carrier-envelope phase-tagged imaging of the controlled electron acceleration from SiO2 nanospheres in intense few-cycle laser fields
New J. Phys., 14 :075010 (July 2012)
Abstract:
Waveform-controlled light fields offer the possibility of manipulating ultrafast electronic processes on sub-cycle timescales. The optical lightwave control of the collective electron motion in nanostructured materials is key to the design of electronic devices operating at up to petahertz frequencies. We have studied the directional control of the electron emission from 95 nm diameter SiO_2 nanoparticles in few-cycle laser fields with a well-defined waveform. Projections of the three-dimensional (3D) electron momentum distributions were obtained via single-shot velocity-map imaging (VMI), where phase tagging allowed retrieving the laser waveform for each laser shot. The application of this technique allowed us to efficiently suppress background contributions in the data and to obtain very accurate information on the amplitude and phase of the waveform-dependent electron emission. The experimental data that are obtained for 4 fs pulses centered at 720 nm at different intensities in the range (1 - 4) × 10^13 W cm^(−2) are compared to quasi-classical mean-field Monte-Carlo simulations. The model calculations identify electron backscattering from the nanoparticle surface in highly dynamical localized fields as the main process responsible for the energetic electron emission from the nanoparticles. The local field sensitivity of the electron emission observed in our studies can serve as a foundation for future research on propagation effects for larger particles and field-induced material changes at higher intensities.
I. Hofmann, J. Meyer-ter-Vehn, X. Yan, and H. Al-Omari
Chromatic energy filter and characterization of laser-accelerated proton beams for particle therapy
Nucl. Instr. Meth. Phys. Res. A, 681 :44 (July 2012)
Abstract:
The application of laser accelerated protons or ions for particle therapy has to cope with relatively large energy and angular spreads as well as possibly significant random fluctuations. We suggest a method for combined focusing and energy selection, which is an effective alternative to the commonly considered dispersive energy selection by magnetic dipoles. Our method is based on the chromatic effect of a magnetic solenoid (or any other energy dependent focusing device) in combination with an aperture to select a certain energy width defined by the aperture radius. It is applied to an initial 6D phase space distribution of protons following the simulation output from a Radiation Pressure Acceleration model. Analytical formula for the selection aperture and chromatic emittance are confirmed by simulation results using the TRACEWIN code. The energy selection is supported by properly placed scattering targets to remove the imprint of the chromatic effect on the beam and to enable well-controlled and shot-to-shot reproducible energy and transverse density profiles.
J. Seres, E. Seres, and C. Spielmann
Classical model of strong-field parametric amplification of soft x rays
Phys. Rev. A, 86 :013822 (July 2012)
Abstract:
We present a detailed theoretical description of laser driven x-ray parametric amplification, which has been experimentally demonstrated by Seres et al. [Nature Phys. 6 455 (2010)] together with a supporting basic model. The process is based on the parametric interaction of an x-ray photon with a laser accelerated electron in a Coulomb field. With the extended model we are able to estimate the gain cross section also for a finite energy distribution of the interacting electrons as well as to consider dephasing between the electrons and the x-ray field. The improved model is capable of describing the recent experimental findings much more accurately.
T. Schlegel, and V. Tikhonchuk
Classical radiation effects on relativistic electrons in ultraintense laser fields with circular polarization
New J. Phys., 14 :073034 (July 2012)
Abstract:
The propagation of a relativistic electron with initial energy ≥ 100 MeV in a number of simple one-dimensional laser field configurations with circular polarization is studied by solving the relativistic equation of motion in the Landau–Lifschitz approach to account for the radiation friction force. The radiation back-reaction on the electron dynamics becomes visible at dimensionless field amplitudes a ≥ 10 at these high particle energies. Analytical expressions are derived for the energy and the longitudinal momentum of the electron, the frequency shift of the light scattered by the electron and the particle trajectories. These findings are compared with the numerical solutions of the basic equations. A strong radiation damping effect results in reduced light scattering, forming at the same time a broad quasi-continuous spectrum. In addition, the electron dynamics in the strong field of a quasistationary laser piston is investigated. Analytical solutions for the electron trajectories in this complex field pattern are obtained and compared with the numerical solutions. The radiation friction force may stop a relativistic electron after propagation over several laser wavelengths at high laser field strengths, which supports the formation of a stable piston.
M. Möller, Y. Cheng, S. Khan, B. Zhao, K. Zhao, M. Chini, G.G. Paulus, and Z. Chang
Dependence of high-order-harmonic-generation yield on driving-laser ellipticity
Phys. Rev. A, 86 :011401 (July 2012)
Abstract:
High-order-harmonic-generation yield is remarkably sensitive to driving laser ellipticity, which is interesting from a fundamental point of view as well as for applications. The most well-known example is the generation of isolated attosecond pulses via polarization gating. We develop an intuitive semiclassical model that makes use of the recently measured initial transverse momentum of tunneling ionization. The model is able to predict the dependence of the high-order-harmonic yield on driving laser ellipticity and is in good agreement with experimental results and predictions from a numerically solved time-dependent Schrödinger equation.
H.-J. Otto, F. Stutzki, F. Jansen, T. Eidam, C. Jauregui, J. Limpert, and A. Tünnermann
Temporal dynamics of mode instabilities in high-power fiber lasers and amplifiers
Opt. Express, 20 :15710 (July 2012)
Abstract:
The temporal behavior of mode instabilities in active large mode area fibers is experimentally investigated in detail. Thus, apart from the onset threshold of mode instabilities, the output beam is characterized using both high-speed camera measurements with 20,000 frames per second and photodiode traces. Based on these measurements, an empiric definition of the power threshold of mode instabilities is introduced. Additionally, it is shown that the temporal dynamics show a transition zone between the stable and the unstable regimes where well-defined periodic temporal fluctuations on ms-timescale can be observed. Finally, it is experimentally shown that the larger the mode-field area, the slower the mode-instability fluctuation is. The observations support the thermal origin of mode instabilities.
B. Döbrich, and A. Eichhorn
Can we see quantum gravity? Photons in the asymptotic-safety scenario
J. High Energ. Phys., 156 :1 (June 2012)
Abstract:
In the search for a quantum theory of gravity it is crucial to find experimental access to quantum gravitational effects. Since these are expected to be very small at observationally accessible scales it is advantageous to consider processes with no tree-level contribution in the standard model, such as photon-photon scattering. We examine the implications of asymptotically safe quantum gravity in a setting with extra dimensions for this case, and point out that various near-future photon-collider setups, employing either electron or muon colliders, or even a purely laser-based setup, could provide a first observational window into the quantum gravity regime.
J. Bierbach, C. Rödel, M. Yeung, B. Dromey, T. Hahn, A. Pour, S. Fuchs, A. E. Paz, S. Herzer, S. Kuschel, O. Jäckel, M.C. Kaluza, G. Pretzler, M. Zepf, and G.G. Paulus
Generation of 10 µW relativistic surface high-harmonic radiation at a repetition rate of 10 Hz
New J. Phys., 14 :065005 (June 2012)
Abstract:
Experimental results on relativistic surface HHG at a repetition rate of 10 Hz are presented. Average powers in the 10 μW range are generated in the spectral range of 51 to 26 nm (24 - 48 eV). The surface harmonic radiation is produced by focusing the second-harmonic of a high-power laser onto a rotating glass surface to moderately relativistic intensities of 3 × 10^19 W cm^−2. The harmonic emission exhibits a divergence of 26 mrad. Together with absolute photon numbers recorded by a calibrated spectrometer, this allows for the determination of the extreme ultraviolet (XUV) yield. The pulse energies of individual harmonics are reaching up to the μJ level, equivalent to an efficiency of 10^−5. The capability of producing stable and intense high-harmonic radiation from relativistic surface plasmas may facilitate experiments on nonlinear ionization or the seeding of free-electron lasers.
C. Jauregui, T. Eidam, H.-J. Otto, F. Stutzki, F. Jansen, J. Limpert, and A. Tünnermann
Physical origin of mode instabilities in high-power fiber laser systems
Opt. Express, 20 :12912 (June 2012)
Abstract:
Mode instabilities, i.e. the rapid fluctuations of the output beam of an optical fiber that occur after a certain output power threshold is reached, have quickly become one of the most limiting effects for the further power scaling of fiber laser systems. Even though much work has been done over the last year, the exact origin of the temporal dynamics of this phenomenon is not fully understood yet. In this paper we show that the origin of mode instabilities can be explained by taking into account the interplay between the temporal evolution of the three-dimensional temperature profile inside of the active fiber and the related waveguide changes that it produces via the thermo-optical effect. In particular it is proposed that non-adiabatic waveguide changes play an important role in allowing energy transfer from the fundamental mode into the higher order mode. As it is discussed in the paper, this description of mode instabilities can explain many of the experimental observations reported to date.
R. Märtin, G. Weber, R. Barday, Y. Fritzsche, U. Spillmann, W. Chen, R. D. DuBois, J. Enders, M. Hegewald, S. Hess, A. Surzhykov, D. B. Thorn, S. Trotsenko, M. Wagner, D. F. A. Winters, V. A. Yerokhin, and T. Stöhlker
Polarization Transfer of Bremsstrahlung Arising from Spin-Polarized Electrons
Phys. Rev. Lett., 108 :26480 (June 2012)
Abstract:
We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. By means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. For the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy.
M. Baumgartl, C. Lecaplain, A. Hideur, J. Limpert, and A. Tünnermann
66 W average power from a microjoule-class sub-100 fs fiber oscillator
Opt. Lett., 37 :1640 (May 2012)
Abstract:
Performance scaling of passively mode-locked ultrashort-pulse fiber oscillators in terms of average power, peak power, and pulse energy is demonstrated. A very-large-mode-area fiber laser in an all-positive group-velocity-dispersion ring cavity configuration with intracavity spectral filter, mode-locked by nonlinear polarization evolution, emits 66 W of average power at 76 MHz repetition rate, corresponding to 0.9 μJ pulse energy. The pulses are dechirped to 91 fs outside the cavity with an average power of 60 W remaining after the compressor. The generated pulse peak power is as high as 7 MW.
B. Bergues, M. Kübel, N. Johnson, B. Fischer, N. Camus, K. Betsch, O. Herrwerth, A. Senftleben, A. Sayler, T. Rathje, T. Pfeifer, I. Ben-Itzhak, R. Jones, G. Paulus, F. Krausz, R. Moshammer, J. Ullrich, and M. Kling
Attosecond tracing of correlated electron-emission in non-sequential double ionization
Nat. Commun., 3 :813 (May 2012)
Abstract:
Despite their broad implications for phenomena such as molecular bonding or chemical reactions, our knowledge of multi-electron dynamics is limited and their theoretical modelling remains a most difficult task. From the experimental side, it is highly desirable to study the dynamical evolution and interaction of the electrons over the relevant timescales, which extend into the attosecond regime. Here we use near-single-cycle laser pulses with well-defined electric field evolution to confine the double ionization of argon atoms to a single laser cycle. The measured two-electron momentum spectra, which substantially differ from spectra recorded in all previous experiments using longer pulses, allow us to trace the correlated emission of the two electrons on sub-femtosecond timescales. The experimental results, which are discussed in terms of a semiclassical model, provide strong constraints for the development of theories and lead us to revise common assumptions about the mechanism that governs double ionization.