1. Department of Electrical and Photonics Engineering Technical University of Denmark Roskilde 4000 Denmark
2. Horiba France SAS Palaiseau 91120 France
3. Department of Health Technology Nanoprobes Technical University of Denmark Kongens Lyngby 2800 Denmark
4. Center for Nanophase Materials Sciences and Materials Science and Technology Division Oak Ridge National Laboratory Oak Ridge TN 37830 USA
5. Department of Physics Technical University of Denmark Kongens Lyngby 2800 Denmark