1. Photonics and Optoelectronics
Group and CeNS, Department of Physics, Ludwig-Maximilians Universität München, 80799 München,
Germany
2. Institute of Physics
and Institute
of Micro- and Nanotechnologies, Ilmenau University of Technology, 98684 Ilmenau, Germany
3. Institute of Applied Physics, Johannes Kepler Universität, 4040 Linz, Austria