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Q: Quantenoptik
Q 413: Quanteneffekte III
Q 413.5: Talk
Thursday, March 7, 2002, 15:00–15:15, HS 01/E02
Towards controlled coupling between a high-Q whispering-gallery mode and a single nanoparticle — •Stephan Götzinger1, Vahid Sandoghdar2, and Oliver Benson1 — 1Humboldt-Universität zu Berlin, Institut für Physik, 10117 Berlin, Germany — 2Laboratorium für physikalische Chemie, ETH Zürich, 8093 Zürich, Switzerland
High-Q whispering-gallery modes (WGM) combined with single nanoparticles are promising candidates for controlled cavity-QED experiments or the realization of a single quantum emitter laser. In the experimental realization of such an experiment, it is very important to precisely control the coupling in order to achieve optimal coupling efficiency without degrading the Q-factor. We use in our experiment techniques common in Scanning Near-field Optical Microscopy to place a fiber tip in the evanescent field of a silica microsphere at a distance of approx. 10 nm to the sphere surface. This allows us to scan the sphere surface at constant height for mode identification and to place the fiber tip at any postion of the evanescent field of the WGM at will.
In a first step we investigated the influence of fiber tips with different diameters on the Q-factor of a fundamental WGM. We found that with an 80 nm tip placed in the intensity maximum of the mode it is possible to maintain a Q-factor as high as 108. Then we studied the coupling of active material. In order to do this we coated a microsphere with CdSe/ZnS nanocrystals and measured their photoluminescence spectrum. A strong modulation of the emission spectrum was observed which demonstrates the coupling of the nanocrystals to the WGMs.