München 2004 – wissenschaftliches Programm

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Q: Quantenoptik und Photonik

Q 40: Laserspektroskopie

Q 40.2: Vortrag

Donnerstag, 25. März 2004, 16:45–17:00, HS 204

Towards single-molecule detection by absorption — •Jacqueline Y.P. Butter and Bert Hecht — Nano-Optics group, Institute for Physics, University of Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland

At cryogenic temperatures many temperature activated processes are frozen out, resulting in extremely sharp zero-phonon lines in fluorescence excitation spectra of certain molecule-matrix systems. The presence of sharp absorption lines is accompanied by the fact that the absorption cross section of a single molecule approaches the theoretical limit for an oscillating dipole. However, the spatial resolution in confocal microscopy is limited by the diffraction limit. Near-field excitation can be used to overcome this limit. Using near-field excitation, the light source can eventually be made smaller than the absorption cross section of a single molecule. The aim of our experiment is to look at the interaction of strongly confined light fields with single molecules. The set up we use, is a combination of a scanning confocal optical microscope and a scanning probe microscope, which is suitable for operation at both room and cryogenic temperature. A single-mode ring dye laser is used to excite the molecules and to perform spectroscopy at cryogenic temperature.