1. INFN, National Institute for Nuclear Physics, Frascati, Italy
2. Institute of Nanosciences CNR-NANO of Modena, Università di Modena and Reggio Emila, Modena, Italy
3. Loughborough University, Loughborough, U.K.
4. INRIM, Italy's National Metrology Institute, Torino, Italy
5. IFN-CNR, Institute for Photonics and Nanotechnologies, Rome, Italy
6. CNR-SPIN, Institute for Superconductivity, Innovative Materials and Devices, Pozzuoli, Italy
7. ISASI-CNR, Institute of Applied Sciences and Intelligent Systems, Pozzuoli, Italy
8. Ruhr-University Bochum, Bochum, Germany
9. Leibniz Institute of Photonic-Technology, Jena, Germany
10. Institute of Nanosciences CNR-NANO, Modena, Italy
11. DMF-Dipartimento di Matematica e Fisica Università della Campania “L. Vanvitelli”, Caserta, Italy
12. Karlsruhe Institute of Technology, Karlsruhe, Germany