1. Department of Photonics Engineering, Technical University of Denmark, DK-4000 Roskilde, Denmark
2. DTU Nanolab, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
3. DTU Energy, Technical University of Denmark, DK-4000 Roskilde, Denmark
4. Department of Physics, University of Oslo, 0371 Oslo, Norway
5. DTU Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark