1. Institute of Physics, Martin Luther University Halle-Wittenberg, Von-Danckelmann Platz 3, 06120 Halle, Germany
2. Fachbereich Physik and Landesforschungszentrum OPTIMAS, Rheinland-Pfälzische Technische Universität Kaiserslautern-Landau, 67663 Kaiserslautern, Germany
3. Department of Materials Science, School of Natural Sciences, University of Patras, 26504 Patras, Greece
4. Photonik Center Kaiserslautern, 67663 Kaiserslautern, Germany
5. National Institute of Materials Physics, Atomistilor 405A, 077125 Magurele, Romania
6. Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece