[1] CNR, Inst Photon & Nanotechnol, IT-35131 Padua, Italy
[2] CNR, Inst Inorgan Methodol & Plasmas, IT-34149 Basovizza, TS, Italy
[3] Sincrotrone Trieste SCpA, I-34149 Basovizza, TS, Italy
[4] Politecn Milan, Dept Phys, IT-20133 Milan, Italy
[5] Univ Nova Gorica, Lab Quantum Opt, SI-5270 Ajdovscina, Slovenia