1. Department of Physics, Pisa University, Largo Bruno Pontecorvo 3, Pisa 56127, Italy
2. CNR — National Institute of Optics, Largo Enrico Fermi 6, 50125 Florence, Italy
3. CNRS, CPT, Université de Toulon, Aix Marseille University, Marseille, France
4. CNR — Institute of Biophysics, Area di Ricerca San Cataldo, Via G. Moruzzi, 1, Pisa 56124, Italy