1. Department of Physics, University of Calabria, via P. Bucci, 31C, 87036 Rende, Cosenza, Italy
2. CNR Nanotec UOS Rende, via P. Bucci, 31D, 87036 Rende, Cosenza, Italy
3. Istituto Italiano di Tecnologia, via Morego 30, 16163 Genova (GE), Italy
4. CNR-ICAR, Institute for High Performance and Networking, via P. Bucci 8-9c, 87036 Rende, Cosenza, Italy
5. Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsarigradsko Chaussee Blvd, 1784 Sofia, Bulgaria
6. CNR-INO and European Laboratory for Non Linear Spectroscopy (LENS), Via Nello Carrara, 1, Sesto Fiorentino, 50019 Firenze (FI), Italy