1. University College Cork, Department of Electrical and Electronic Engineering, Ireland
2. University of Pennsylvania, Department of Physics and Astronomy, 209 S 33rd Street, Philadelphia, PA 19104, USA.
3. Gesellschaft für Schwerionenforschung, Planckstr. 1, D-64291, Darmstadt, Germany
4. Centre National de la Recherche Scientifique, Laboratory for Photonics and Nanostructures, Route de Nozay, F-91460 Marcoussis, France
5. Université d’Évry Val d’Essonne, Laboratoire MPI, Bd. François Mitterrand, F-91025 Évry, France