1. Optical
Nanomaterial Group, Institute for Quantum Electronics, Department
of Physics, ETH Zurich, August-Piccard-Hof 1, 8093 Zurich, Switzerland
2. Institute
of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University, Max-Wien-Platz 1, 07743 Jena, Germany
3. Nonlinear
Physics Center, Research School of Physics and Engineering, Australian National University, Canberra, ACT 0200, Australia