1. Max Planck Institute for the Science of Light , Erlangen, Germany.
2. Institute for Optics, Information and Photonics, University Erlangen-Nürnberg , Erlangen, Germany.
3. SAOT, School in Advanced Optical Technologies , Erlangen, Germany.
4. Department of Physics, University of Otago , Dunedin, New Zealand.
5. Department of Physics, Technical University of Denmark , Lyngby, Denmark.