12.septembril 2013 kell 14.15
Ettekanne: Prof. S.K. Sekatskii
Laboratoire de Physique de la Matière Vivante, IPSB, Ecole Polytechnique Fédérale de Lausanne, Lausanne, CH 1015, Switzerland
Fluorescence Resonance Energy Transfer Scanning Near-field Optical Microscopy: from spatial superresolution to quantum computing
In recent years, a few groups presented first Fluorescence Resonant Energy Transfer Scanning Near-field Optical Microscopy (FRET SNOM) images. However, to realize all advantages of the method , truly single – molecule FRET SNOM images should be obtained: the task which proved to be difficult due to the limiting photostability of the fluorescent centers and rapid damage of the “FRET – active” SNOM probes. Here we present what we believe are the first FRET SNOM single molecule images obtained using CdSe nanocrystals as donors (these are spin – coated onto glass slide surface) and AlexaFluor 594 or Texas Red dye molecules as acceptors (these are incorporated into the “self sharpening pencil - type” probes based on thin polystyrene layers stained with dye molecules deposited onto SNOM tip apex) . Very rapid scanning available with our new SNOM exploring “double-resonant montage” of a fiber probe onto the tuning fork was used (SNOM image of an area with the sizes of 200 – 300 nm is recorded during 10 - 30 seconds), which enables to overcome the photostability problem. Additional advantage consists in the following. Such a fast scanning rate for standard 256 x 256 or 128 x 128 pixel images corresponds to expositions of the order of 0.1 – 2 ms/pixel, hence for typical noise level less than 1000 counts/s we obtain essentially “completely dark background area” (the most pixels contain zero counts) which enables to distinguish isolated single molecules as “extended non-dark spots”. Spatial resolution of the order of 10 – 20 nm is achieved .
We also present first experimental results obtained in the field related with coherent FRET SNOM quantum computing [3, 4]. Low temperature (4 – 8 K) pump – probe laser spectroscopy of resonantly interacting trivalent neodymium ions in calcium fluoride crystal (so called M-centers; these are nothing else than donor – acceptor pairs subject to coherent FRET interaction with the decoherence time of ca. 6 ns which is longer than laser pulse duration) reveals the preparation of Bell’s fully entangled vacuum – single exciton and vacuum – double exciton states.
Finally, in relation with the SCOPES grant under the preparation, our recent results concerning ultrasensitive Photon Crystal Electromagnetic waves – based optical detector [5, 6] and its relation with SNOM technique will be briefly presented.
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