Biomedical subjects
Publications and source records attributed to K Holldack.
At the 1.7-GeV electron storage ring BESSY II, a first source of synchrotron radiation with 100 fs pulse duration, variable (linear and circular) polarization, tunable photon energy (300 to 1400 eV), and excellent signal-to-background ratio was constructed and is now in routine operation.
Femtosecond far-infrared radiation pulses in the THz spectral range were observed as a consequence of the energy modulation of 1.7 GeV electrons by femtosecond laser pulses in the BESSY storage ring in order to generate femtosecond x-ray pulses ("femtoslicing"). In addition to being crucial for diagnostics of the laser-electron interaction, the THz radiation itself is useful for experiments where intense ultrashort THz pulses of well-defined temporal and spectral characteristics are required.
We present a model describing high power stable broadband coherent synchrotron radiation (CSR) in the terahertz frequency region in an electron storage ring. The model includes distortion of bunch shape from the synchrotron radiation (SR), which enhances higher frequency coherent emission, and limits to stable emission due to an instability excited by the SR wakefield. It gives a quantitative explanation of several features of the recent observations of CSR at the BESSY II storage ring. We also use this model to optimize the performance of a source for stable CSR emission.
A new technology for generating steady state, brilliant, broadband, coherent, far-infrared (FIR) radiation in electron storage rings is presented, suitable for FIR spectroscopy. An FIR power increase of up to 100 000 compared to the normal, incoherent synchrotron radiation in the range of approximately 5 to approximately 40 cm(-1) could be achieved. The source is up to 1000 times more brillant compared to a standard Hg arc lamp. The coherent synchrotron radiation is produced in a "low alpha" optics mode of the synchrotron light source BESSY, by bunch shortening and non-Gaussian bunch deformation.
At BESSY II it is demonstrated that far-infrared coherent synchrotron radiation (CSR) can be generated by a controlled, steady-state process at storage rings. As an indication for coherent emission, the radiated power grows with the square of the beam current. The spectrum was analyzed by an interferometer in the 1-mm to 0.3-mm wavelength range. The CSR was enhanced more than 3000 times above background; the incoherent radiation remained below the background level. Steady-state and bursting CSR were discriminated by time resolved analysis from micro seconds to seconds.
For BESSY II, synchrotron radiation beam diagnostics will be incorporated in both the insertion-device front ends and the dipole-beamline front ends. In order to gain a complete picture of the source characteristics, a diagnostic front end has been designed and tested for dipole radiation. This consists of (i) a pinhole array imaging system, (ii) a double-blade system for the determination of the vertical center of gravity of the synchrotron radiation fan, and (iii) a Bragg-Fresnel multilayer system for the most precise image information about the source size and shape.
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The appearance of carotid atrial sounds has been observed in 6 out of 19 patients with stroke. It is assumed that these patients have obstructions in the carotid-subclavian area. Further studies to prove this working hypothesis are in progress.
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By means of clinical studies the frequency of cerebral embolic incidents after myocardial infarction was clarified. It is referred to the importance of some risk factors. The value of long time anticoagulant therapy is discussed.
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