@article{CzerniukBrueggemannTepperetal.2014,
  author    = {Czerniuk, T. and Br{\"u}ggemann, C. and Tepper, J. and Brodbeck, S. and Schneider, C. and Kamp, M. and H{\"o}fling, S. and Glavin, B. A. and Yakovlev, D. R. and Akimov, A. V. and Bayer, M.},
  title     = {Lasing from active optomechanical resonators},
  series = {Nature Communications},
  volume    = {5},
  journal   = {Nature Communications},
  doi       = {10.1038/ncomms5038},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-121559},
  pages     = {4038},
  year      = {2014},
  abstract  = {Planar microcavities with distributed Bragg reflectors (DBRs) host, besides confined optical modes, also mechanical resonances due to stop bands in the phonon dispersion relation of the DBRs. These resonances have frequencies in the 10- to 100-GHz range, depending on the resonator's optical wavelength, with quality factors exceeding 1,000. The interaction of photons and phonons in such optomechanical systems can be drastically enhanced, opening a new route towards the manipulation of light. Here we implemented active semiconducting layers into the microcavity to obtain a vertical-cavity surface-emitting laser (VCSEL). Thereby, three resonant excitations--photons, phonons and electrons--can interact strongly with each other providing modulation of the VCSEL laser emission: a picosecond strain pulse injected into the VCSEL excites long-living mechanical resonances therein. As a result, modulation of the lasing intensity at frequencies up to 40 GHz is observed. From these findings, prospective applications of active optomechanical resonators integrated into nanophotonic circuits may emerge.},
  language  = {en}
}
@article{Graetz2021,
  author    = {Graetz, Jonas},
  title     = {Simulation study towards quantitative X-ray and neutron tensor tomography regarding the validity of linear approximations of dark-field anisotropy},
  series = {Scientific Reports},
  volume    = {11},
  journal   = {Scientific Reports},
  doi       = {10.1038/s41598-021-97389-y},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-261844},
  year      = {2021},
  abstract  = {Tensor tomography is fundamentally based on the assumption of a both anisotropic and linear contrast mechanism. While the X-ray or neutron dark-field contrast obtained with Talbot(-Lau) interferometers features the required anisotropy, a preceding detailed study of dark-field signal origination however found its specific orientation dependence to be a non-linear function of the underlying anisotropic mass distribution and its orientation, especially challenging the common assumption that dark-field signals are describable by a function over the unit sphere. Here, two approximative linear tensor models with reduced orientation dependence are investigated in a simulation study with regard to their applicability to grating based X-ray or neutron dark-field tensor tomography. By systematically simulating and reconstructing a large sample of isolated volume elements covering the full range of feasible anisotropies and orientations, direct correspondences are drawn between the respective tensors characterizing the physically based dark-field model used for signal synthesization and the mathematically motivated simplified models used for reconstruction. The anisotropy of freely rotating volume elements is thereby confirmed to be, for practical reconstruction purposes, approximable both as a function of the optical axis' orientation or as a function of the interferometer's grating orientation. The eigenvalues of the surrogate models' tensors are found to exhibit fuzzy, yet almost linear relations to those of the synthesization model. Dominant orientations are found to be recoverable with a margin of error on the order of magnitude of 1 degrees. Although the input data must adequately address the full orientation dependence of dark-field anisotropy, the present results clearly support the general feasibility of quantitative X-ray dark-field tensor tomography within an inherent yet acceptable statistical margin of uncertainty.},
  language  = {en}
}
@article{MaassBentmannSeibeletal.2016,
  author    = {Maaß, Henriette and Bentmann, Hendrik and Seibel, Christoph and Tusche, Christian and Eremeev, Sergey V. and Peixoto, Thiago R.F. and Tereshchenko, Oleg E. and Kokh, Konstantin A. and Chulkov, Evgueni V. and Kirschner, J{\"u}rgen and Reinert, Friedrich},
  title     = {Spin-texture inversion in the giant Rashba semiconductor BiTeI},
  series = {Nature Communications},
  volume    = {7},
  journal   = {Nature Communications},
  doi       = {10.1038/ncomms11621},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173769},
  year      = {2016},
  abstract  = {Semiconductors with strong spin-orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices. Unveiling the full spin texture in momentum space for such materials and its relation to the microscopic structure of the electronic wave functions is experimentally challenging and yet essential for exploiting spin-orbit effects for spin manipulation. Here we employ a state-of-the-art photoelectron momentum microscope with a multichannel spin filter to directly image the spin texture of the layered polar semiconductor BiTeI within the full two-dimensional momentum plane. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the valence and conduction band electrons in BiTeI have spin textures of opposite chirality and of pronounced orbital dependence beyond the standard Rashba model, the latter giving rise to strong optical selection-rule effects on the photoelectron spin polarization. These observations open avenues for spin-texture manipulation by atomic-layer and charge carrier control in polar semiconductors.},
  language  = {en}
}