1. The Laser Zentrum Hannover e.V., 30419 Hannover, Germany
2. The Optical Sensors Laboratory, National Centre for Sensor Research, Dublin City University, Dublin 9, Ireland
3. Institute of Electronic Structure and Laser, Foundation for Research and Technology - Hellas, P.O. Box 1527, 711 10 Heraklion, Greece
4. Department of Physics, University of Crete, 71003 Heraklion, Crete, Greece
5. Department of Materials Science and Technology, University of Crete, 710 03 Heraklion, Crete, Greece