[1] LudwigMaximilians Univ Munchen, Fac Phys, Nanoinst Munich, Chair Hybrid Nanosyst, D-80539 Munich, Germany
[2] Imperial Coll London, Dept OfPhys, London SW7 2AZ, England
[3] Macquarie Univ, MQ Photon Res Ctr, Dept Phys & Astron, N Ryde, NSW, Australia