Karsten Holldack

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The rapidly increasing information density required of modern magnetic data storage devices raises the question of the fundamental limits in bit size and writing speed. At present, the magnetization reversal of a bit can occur as quickly as 200 ps (ref. 1). A fundamental limit has been explored by using intense magnetic-field pulses of 2 ps duration leading(More)
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(More)
Frequency domain Fourier transform THz electron paramagnetic resonance (FD-FT THz-EPR) based on coherent synchrotron radiation (CSR) is presented as a novel tool to ascertain very large zero field splittings in transition metal ion complexes. A description of the FD-FT THz-EPR at the BESSY II storage ring providing CSR in a frequency range from 5 cm(-1) up(More)
We have investigated the single-molecule magnets [Mn(III)2 (5-Brsalen)2 (MeOH)2 M(III) (CN)6 ]NEt4 (M=Os (1) and Ru (2); 5-Brsalen=N,N'-ethylenebis(5-bromosalicylidene)iminate) by frequency-domain Fourier-transform terahertz electron paramagnetic resonance (THz-EPR), inelastic neutron scattering, and superconducting quantum interference device (SQUID)(More)
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(More)
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(More)
Irradiating a ferromagnet with a femtosecond laser pulse is known to induce an ultrafast demagnetization within a few hundred femtoseconds. Here we demonstrate that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently. We optically excite a(More)
Photon beams of 99 eV energy carrying orbital angular momentum (OAM) have been observed in the 2nd harmonic off-axis radiation of a helical undulator at the 3rd generation synchrotron radiation light source BESSY II. For detection, the OAM carrying photon beam was superimposed with a reference beam without OAM. The interference pattern, a spiral intensity(More)