D. Bauer

Max Planck Institute for Nuclear Physics, Heidelburg, Baden-Württemberg, Germany

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Publications (31)52 Total impact

  • P. Mulser, D. Bauer
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    ABSTRACT: Superintense laser beam absorption in dense matter is governed by collisionless processes. During the last two decades various attempts have been made to explain the high degrees of absorption found in experiments and computer simulations and partial successes have been achieved. Here we present the model of anharmonic resonance and show its capability to explain the underlying physics of collisionless absorption in all its essential aspects, in particular the origin of the phase shift between driver field and induced current and the origin of prompt fast electrons.
    Proceedings of the The 2nd International Conference on ultra-intense laser interaction science, AIP, 75-78 (2010). 02/2010;
  • P Mulser, D Bauer
    01/2010; Springer-Verlag Berlin.
  • P. Mulser, D. Bauer
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    ABSTRACT: Collisionless absoption of ultrashort intense laser pulses in overdense matter and clusters is shown to be accomplished by anharmonic resonance. It is capable of explaining all basic absorption characteristics (phase shifts, high efficiency, fast electrons, polarization differences) and of making valuable predictions for applications.
    Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest (2009). 08/2009;
  • P Mulser, D Bauer, H Ruhl
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    ABSTRACT: After two decades of experiments with intense fs laser pulses the physical mechanism of collisionless absorption in overdense matter is still not understood. We show that anharmonic resonance in the self-generated plasma potential at a steep ion density profile may represent the leading physical absorption mechanism. Resonance provides for the phase shift of the free electron current which is compulsory for laser beam energy transfer to any medium and is capable of explaining the prompt generation of fast electrons with maximum energies exceeding many times their quiver energy, and the polarization dependence.
    Physical Review Letters 12/2008; 101(22):225002. · 7.73 Impact Factor
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    P. Mulser, D. Bauer, H Ruhl
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    ABSTRACT: Two decades after the invention of chirped pulse amplification the physical mechanism of collisionless absorption of intense laser radiation in overdense matter is still not sufficiently well understood. We show that anharmonic resonance in the self-generated plasma potential of the single plasma layers (cold plasma model) or of the individual electrons (warm plasma), respectively, constitutes the leading physical mechanism of collisionless absorption in an overdense plasma. Analogously to collisions, resonance provides for the finite phase shift of the free electron current relative to the driving laser field which is compulsory for energy transfer from the laser beam to any medium. An efficient new scenario of wave breaking is also indicated.
    06/2008;
  • D. Bauer, P. Mulser
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    ABSTRACT: The crossing of the narrow skin layer in solid targets by electrons in a time shorter than a laser cycle represents one of the numerous collisionless absorption mechanisms of intense laser-matter interaction. This kinetic effect is studied at normal and oblique laser beam incidence and particle injection by a test particle approach in an energy interval extending into the relativistic domain. Three main results obtained are the strong dependence of the energy gain by the single particle on the instant of injection relative to the phase of the light wave, the reflection of the particles primarily contributing to absorption well in front of the target rather than in the Debye layer, and the low degree of absorption hardly exceeding the 10% limit. The simulation results offer a more unambiguous interpretation of the absorption mechanism often referred to as “vacuum heating.” In particular, it is clearly revealed that the absorption in the vacuum region prevails on that originating from the skin layer. Relativistic ponderomotive effects are also tested, however their contribution to absorption is not significant.
    Physics of Plasmas 02/2007; 14(2):023301-023301-11. · 2.38 Impact Factor
  • P. Mulser, D. Bauer
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    ABSTRACT: The leading physical mechanism responsible for collisionless absorption of intense laser radiation in overdense matter (solids, liquids, clusters, aerosols) is addressed and discussed in detail. It is shown that the plasma layers become anharmonic oscillators with variable eigenfrequency under the strong driving field and can therefore enter into resonance with it. Already existing collisionless absorption models are discussed in the light of the new mechanism. © 2006 American Institute of Physics
    AIP Conference Proceedings. 04/2006; 827(1):15-25.
  • P. Mulser, D. Bauer, Tatjana Muth
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    ABSTRACT: The status of present understanding of collisionless absorption of intense laser pulses out of linear resonance is discussed in Sec. 1. In Sec. 2 skin layer absorption is modelled in a test particle picture and it is shown that the energy gained by a single particle depends strongly on the injection phase relative to the laser field and that electron reflection is not localized at the target boundary. To provide for adequate absorption an energetic component must be present. The main achievement of this paper is contained in Sec. 3. We show that most of collective (collisionless) absorption is by anharmonic resonance of electron bunches in their own space charge field. In Sec. 4 basic considerations on electron acceleration by laser beams in vacuum are outlined and a summary of the main achievements by wake field acceleration in tenuous plasmas is presented.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    02/2006;
  • D Bauer, P Mulser
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    ABSTRACT: A particle can gain appreciable irreversible energy ("absorption") from linear or nonlinear oscillations only by ballistic excitation ("collision") or, if excited by an adiabatic pulse of constant frequency, by undergoing resonance. For the linear oscillator it is shown that the transition from ballistic to adiabatic behavior out of resonance occurs for sin2-pulses 2–4 eigenperiod long. In the case of a linear oscillator with time-varying eigenfrequency it is shown that Cornu's double spiral represents an attractor, either for zero energy gain out of resonance or finite gain by transiting through resonance. One of the remarkable properties of nonlinear oscillators is that resonance depends on the level of excitation. It is this property which opens a new access to understanding the dominant heating process at high laser intensities, the so-called collisionless absorption phase in solids, extended cluster media, dusty plasmas, and sprays, well guaranteed by experiments and computer simulations but hitherto not well understood in physical terms.
    Journal of Physics Conference Series 07/2005; 11(1):169.
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    D Bauer
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    ABSTRACT: The interaction of short laser pulses with small rare gas clusters is investigated by using a microscopic, semi-classical model with an explicit treatment of the inner-atomic dynamics. Field and collisional ionization as well as recombination are incorporated self-consistently so that the use of rates for these processes could be avoided. The laser absorption and ionization mechanisms in clusters at near-infrared (800 nm) and VUV wavelengths (100 nm) are analysed.
    Journal of Physics B Atomic Molecular and Optical Physics 07/2004; 37(15):3085. · 2.03 Impact Factor
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    ABSTRACT: The generation of harmonics by atoms interacting with two laser fields having coplanar circular polarizations and an integral frequency ratio is addressed through ab initio numerical simulations. A detailed characterization of a few specific harmonics is given. In particular, the two different cases where the total energy absorbed through photons is far off or close to the energy gap between different atomic states are investigated. It is found that the conversion efficiency in the harmonic generation is strongly dependent on the inner atomic structure and in certain specific cases it can be significantly enhanced within a small frequency range.
    Applied Physics B 04/2004; 78(7):851-854. · 1.78 Impact Factor
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    D. Bauer
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    ABSTRACT: Semi-classical molecular dynamics simulations of small rare gas clusters in short laser pulses of 100nm wavelength were performed. For comparison, the cluster response to 800nm laser pulses was investigated as well. The inner ionization dynamics of multi-electron atoms inside the cluster was treated explicitly. The simulation results underpin the belief that at XUV (extreme ultraviolet) wavelengths collisions play an important role in the energy absorption. The generation of the surprisingly high charge states of Xe atoms inside clusters, as they were observed in a free-electron laser experiment at DESY, Hamburg, Germany by Wabnitz et al. is due to the reduced ionization potential of atoms inside charged clusters, the ionization ignition mechanism, and collisions.
    Applied Physics B 04/2004; 78(7):801-806. · 1.78 Impact Factor
  • P.  MULSER , D.  BAUER 
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    ABSTRACT: The concept of fast ignition of precompressed pellets for inertial confinement fusion is presented and the main approaches are discussed. Numerical simulations of fast coronal ignition and the peculiarities of this scheme are considered in detail. Particular attention is devoted to the energy transport in the pellet corona. It is shown that fast coronal ignition will be successful only if the energy deposition by the fast electrons is anomalous over a sufficiently extended overdense region. Alternative schemes are briefly discussed.
    Laser and Particle Beams 02/2004; 22(01):5 - 12. · 2.02 Impact Factor
  • D.  BAUER 
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    ABSTRACT: Optical field ionization is the earliest and fastest plasma-generating process during the interaction of intense laser light with matter. By using short and rapidly rising laser pulses, the free electron density may turn from being transparent for an incoming laser pulse to reflective in less than half a laser cycle, that is, on a subfemtosecond timescale. Extremely nonlinear optical effects arise as a consequence of this. In this article, the basics of optical field ionization that are relevant in analytical or numerical studies of intense laser–matter interactions are reviewed. Several macroscopic effects of field ionization in the interaction of intense laser pulses with solid targets are briefly surveyed.
    Laser and Particle Beams 09/2003; 21(04):489 - 495. · 2.02 Impact Factor
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    D. Bauer, A. Macchi
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    ABSTRACT: The electron dynamics of rare gas clusters in laser fields is investigated quantum mechanically by means of time-dependent density functional theory. The mechanism of early inner and outer ionization is revealed. The formation of an electron wave packet inside the cluster shortly after the first removal of a small amount of electron density is observed. By collisions with the cluster boundary the wave packet oscillation is driven into resonance with the laser field, hence leading to higher absorption of laser energy. Inner ionization is increased because the electric field of the bouncing electron wave packet adds up constructively to the laser field. The fastest electrons in the wave packet escape from the cluster as a whole so that outer ionization is increased as well. Comment: 8 pages, revtex4, PDF-file with high resolution figures is available from http://mitarbeiter.mbi-berlin.de/bauer/publist.html, publication no. 24. Accepted for publication in Phys. Rev. A
    Physical Review A 04/2003; · 3.04 Impact Factor
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    ABSTRACT: The generation of harmonics by atoms or ions in a two-color, coplanar field configuration with commensurate frequencies is investigated through both, an analytical calculation based on the Lewenstein model and the numerical ab initio solution of the time-dependent Schroedinger equation of a two-dimensional model ion. Through the analytical model, selection rules for the harmonic orders in this field configuration, a generalized cut-off for the harmonic spectra, and an integral expression for the harmonic dipole strength is provided. The numerical results are employed to test the predictions of the analytical model. The scaling of the cut-off as a function of both, one of the laser intensities and frequency ratio $\eta$, as well as entire spectra for different $\eta$ and laser intensities are presented and analyzed. The theoretical cut-off is found to be an upper limit for the numerical results. Other discrepancies between analytical model and numerical results are clarified by taking into account the probabilities of the absorption processes involved. Comment: 8 figures
    Physical Review A 11/2002; · 3.04 Impact Factor
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    ABSTRACT: Computational studies of many-electron systems in strong laser fields are presented. The ionization and nonlinear dipole response of the ball-shaped C60 fullerene molecule are investigated with a time-dependent density functional approach and a jellium approximation for the ionic background. We find that C60 ionization at 800 nm wavelength occurs multiphoton-like rather than via excitation of a “giant” resonance. Harmonic generation from the interaction of a circularly polarized laser field and a molecule with a discrete rotational symmetry is also studied, and spectra and selection rules are interpreted via a general group theory approach. © 2002 American Institute of Physics.
    AIP Conference Proceedings. 04/2002; 611(1):276-281.
  • P. Mulser, H. Ruhl, S. Hain, D. Bauer
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    ABSTRACT: An alternative scheme of fast ignition is proposed and the key issue of dense matter heating, common to all fast ignition schemes, is discussed. .
    01/2002;
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    ABSTRACT: We discuss harmonic generation in the case of laser field-dressed Hamiltonians that are invariant under so-called dynamical symmetry operations. Examples for such systems are molecules which exhibit a discrete rotational symmetry of order N (e.g. benzene with N=6) interacting with a circularly polarized laser field and single atoms in a bichromatic field, with the two lasers having circular polarizations. Within a general group theory approach we study the harmonics one obtains from the interaction of a laser pulse and a circular molecule. When the system is in a pure field-dressed state the known selection rule kN \pm 1, k=1,2,3, ... results. However, other lines are observed when recombinations with states of a symmetry different from the initial one become important. This is the case for realistic laser pulses (i.e., with a finite duration). In particular when the fundamental laser frequency (or one of its multiples) is resonant with a transition between field-dressed states. Numerical ab initio simulations, confirming our analytical calculations and illustrating the power of the group theory approach, are presented. Comment: Submitted to Journal of Physics B
    Journal of Physics B Atomic Molecular and Optical Physics 07/2001; · 2.03 Impact Factor
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    ABSTRACT: We study the interaction of strong femtosecond laser pulses with the C$_{60}$ molecule employing time-dependent density functional theory with the ionic background treated in a jellium approximation. The laser intensities considered are below the threshold of strong fragmentation but too high for perturbative treatments such as linear response. The nonlinear response of the model to excitations by short pulses of frequencies up to 45eV is presented and analyzed with the help of Kohn-Sham orbital resolved dipole spectra. In femtosecond laser pulses of 800nm wavelength ionization is found to occur multiphoton-like rather than via excitation of a ``giant'' resonance. Comment: 14 pages, including 1 table, 5 figures
    Physical Review A 06/2001; · 3.04 Impact Factor

Publication Stats

374 Citations
52.00 Total Impact Points

Institutions

  • 2005–2008
    • Max Planck Institute for Nuclear Physics
      Heidelburg, Baden-Württemberg, Germany
  • 1998–2004
    • Technical University Darmstadt
      • Institut für Angewandte Physik
      Darmstadt, Hesse, Germany
  • 2000
    • Università di Pisa
      • Department of Physics "E.Fermi"
      Pisa, Tuscany, Italy