1. DTU Fotonik, Technical University of Denmark, Ørsteds Plads 343, DK-2800 Kongens Lyngby, Denmark
2. National Physical Laboratory, Hampton Road, Teddington TW11 0LW, U.K.
3. Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
4. Capres A/S, Diplomvej 373, DK-2800 Kongens Lyngby, Denmark