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Intense local fields around engineered metallic nanostructures are currently of a great interest for many different applications including sensing or enhanced spectroscopy. The resonances characteristics can be tuned by the size, shape, optical frequency and the incident polarization. Recent studies have reported on different designs able to combine strong confinement and enhancement of the electromagnetic field [1,2].
Passive probing of the local field around such structures is not easily achievable due to the high sensitivity of their resonances to their surrounding. In this work we combine different techniques [3]; near field optical scanning microscopy (NSOM) and single fluorescent molecules probing, to investigate gold dimers and nano-antennas [4], fabricated by e-beam lithography.
While, NSOM measurements provide information on the near field components of the local field, the probe interaction needs to be taken into account. A confocal setup with integrated single molecule detection is also used to first image the luminescence of individual dimers. Next, we exploit single fluorescent molecules as non-perturbative vectorial point detectors to map the local 3D field enhancement, with nanometric precision [5]. Individual fluorphores are spread over the sample and are studied in terms of molecular position, orientation, fluorescence brightness and lifetime. Recent results will be presented.
[1] P. Ghenuche, et al, Opt. Lett. 30, 1882 (2005).
[2] C. E. Talley, et al, Nanoletters 5, 1569 (2005).
[3] A.L. Lereu, et al, J. Microsc. Special NFO9 issue (2007).
[4] S. Enoch, et al, Opt. Express 12, 3422 (2004).
[5] N.F. van Hulst, et al, J. Chem. Phys. 112, 7799 (2000).
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