Affiliation: | a Max-Planck Institut für Mikrostrukturphysik, Weinberg 2, 06120, Halle, Germany b Nanophotonic Materials Group, Department of Physics, University of Paderborn, Paderborn, Germany c INFM and Dipartimento di Fisica A. Volta, Università di Pavia, Via Bassi 6, 27100, Pavia, Italy d DLR Stuttgart, Institut für Technische Physik, Theoretische Quantenelektronik, Pfaffenwaldring 38-40, 70569, Stuttgart, Germany e Advanced Technology Institute, School of Electronics and Physical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK |