1. Institute of Electronic Structure and Laser (IESL), Foundation for Research and Technology Hellas (FORTH), P.O. Box 527, Vassilika Vouton, 711 10 Heraklion, Crete, Greece, National Institute for Lasers, Plasma and Radiation Physics (NILPRP), Romania, Department of Materials Science and Technology, University of Crete, Greece, Department of Physics, University of Crete, Greece, and Laser Zentrum Hannover e.V., Hollerithallee 8, D-30419 Hannover, Germany