1. Départment de Physique, Université Libre de Bruxelles (ULB), CP 231, Campus Plaine, Bruxelles 1050, Belgium
2. Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Colom 11, Terrassa 08222 (Barcelona), Spain
3. Brussels Photonics Team, Department of Applied Physics and Photonics (B-PHOT TONA), Vrije Unversiteit Brussels, Pleinlaan 2, Brussels 1050, Belgium
4. Institute of Solid State Physics, 72 Tzarigradsko Chaussee Boulevard, Sofia 1784, Bulgaria
5. Weierstrass Institute, Mohrenstrasse 39, Berlin 10117, Germany
6. Departamento de Física, FCFM, Universidad de Chile, Blanco Encalada 2008, Santiago, Chile