Biomedical subjects

Joachim Burgdörfer

Publications and source records attributed to Joachim Burgdörfer.

6 recordsLinked to original sources

PubMed2006

Laser-cluster interaction: x-ray production by short laser pulses.

We investigate the heating of the quasifree electrons in large rare-gas clusters (N exceeding 10(5) atoms) by short laser pulses at moderate intensities (I approximately = 10(15) W cm(-2)). We identify elastic large-angle backscattering of electrons at ionic cores in the presence of a laser field as an efficient heating mechanism. Its efficiency as well as the effect of collective electron motion, electron-impact ionization, and cluster charging are studied employing a mean-field classical transport simulation. Results for the absolute x-ray yields are in surprisingly good quantitative agreement with recent experimental results.

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PubMed2005

Enhancement of low energy electron-ion recombination in a magnetic field: influence of transient field effects.

Electron-ion recombination observed in storage ring experiments shows a strong enhancement relative to what standard radiative recombination rates predict. We simulate the effect of a transient motional electric field induced by the merging of an electron and an ion beam in the electron cooler which opens an additional pathway for free-bound transitions of electrons. We show that the measured rate contains a significant contribution from radiative stabilization of Rydberg states formed by this transient motional electric field. The absolute excess recombination rates obtained are in good agreement with the experimental data. The scaling of the rate with the ion charge and the magnetic guiding field is analyzed.

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PubMed2005

Pseudopath semiclassical approximation to transport through open quantum billiards: Dyson equation for diffractive scattering.

We present a semiclassical theory for transport through open billiards of arbitrary convex shape that includes diffractively scattered paths at the lead openings. Starting from a Dyson equation for the semiclassical Green's function we develop a diagrammatic expansion that allows a systematic summation over classical and pseudopaths, the latter consisting of classical paths joined by diffractive scatterings ("kinks"). This renders the inclusion of an exponentially proliferating number of pseudopath combinations numerically tractable for both regular and chaotic billiards. For a circular billiard and the Bunimovich stadium the path sum leads to a good agreement with the quantum path length power spectrum up to long path length. Furthermore, we find excellent numerical agreement with experimental studies of quantum scattering in microwave billiards where pseudopaths provide a significant contribution.

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PubMed2005

Shot noise in the chaotic-to-regular crossover regime.

We investigate the shot noise for phase-coherent quantum transport in the chaotic-to-regular crossover regime. Employing the modular recursive Green's function method for both ballistic and disordered two-dimensional cavities, we find the Fano factor and the transmission eigenvalue distribution for regular systems to be surprisingly similar to those for chaotic systems. We argue that, in the case of regular dynamics in the cavity, diffraction at the lead openings is the dominant source of shot noise. We also explore the onset of the crossover from quantum-to-classical transport and develop a quasiclassical transport model for shot noise suppression which agrees with the numerical quantum data.

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PubMed2005

Time resolved Fano resonances.

Recent advances in the generation of sub-fs extreme ultraviolet pulses and attosecond metrology have opened up the possibility to trace the time evolution of electronic wave packets inside atoms in pump-probe experiments. We investigate the feasibility of observing the buildup of a Fano resonance in the time domain by attosecond streaking techniques. A time-resolved resonance is initialized by a sub-fs extreme ultraviolet-pump pulse in the presence of a synchronized phase-controlled probe laser pulse. The time evolution of the coherent superposition of resonant state and continuum is mapped onto a modulation of the electron spectrum as a function of the time delay between pump and probe pulse. (super-)Coster-Kronig transitions with lifetimes of approximately 400 asec( are identified as prime candidates.

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PubMed2003

Semiclassical theory for transmission through open billiards: convergence towards quantum transport.

We present a semiclassical theory for transmission through open quantum billiards which converges towards quantum transport. The transmission amplitude can be expressed as a sum over all classical paths and pseudopaths which consist of classical path segments joined by "kinks," i.e., diffractive scattering at lead mouths. For a rectangular billiard we show numerically that the sum over all such paths with a given number of kinks K converges to the quantum transmission amplitude as K--> infinity. Unitarity of the semiclassical theory is restored as K approaches infinity. Moreover, we find excellent agreement with the quantum path-length power spectrum up to very long path length.

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