1. Dipartimento di Ingegneria “Enzo Ferrari,” Università di Modena e Reggio Emilia, via P. Vivarelli 10, 41125 Modena, Italy
2. IOM-CNR Institute, Area Science Park, SS 14 Km, 163.5, Basovizza, 34149 Trieste, Italy
3. Department of Physics, Centre for Photonics and Photonic Materials (CPPM), University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
4. Material and Chemical Characterisation Facility (MC2), University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
5. Dipartimento di Scienze, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146 Roma, Italy
6. Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa