1. ETH Zurich, Department of Physics, Institute for Quantum Electronics, Optical Nanomaterial Group, 8093 Zurich, Switzerland
2. Univ. Lyon, CNRS, ECL, INSA Lyon, UCBL, CPE Lyon, INL, UMR 5270, 69130 Ecully, France
3. University of Technology Sydney, School of Mathematical and Physical Sciences, Ultimo, New South Wales 2007, Australia