Single-metal-cluster local imaging: polarized scattered electric field calculation compared to the field’s modulus and phase observed in the optical near-field |
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Authors: | S Grésillon R Lecaque L Williame JC Rivoal |
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Institution: | (1) ESPCI, Laboratoire de Spectroscopie en Lumiere Polarisee UPR5-CNRS and University P. et M. Curie, 10 rue Vauquelin, 75231 Paris Cedex 05, France |
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Abstract: | Simultaneous topographical and near-field optical imaging have been performed on single gold particles of diameters close
to 12 nm. The optical source is a linearly polarized laser diode operating at λ=780 nm away from the plasmon resonance of
the particles. The experimental optical image is recorded with an apertureless scanning near-field optical microscope (ASNOM)
operating in transmission mode. It is compared to the components of the polarized scattered electric field around a single
cluster calculated using Mie formalism. We show that the tip used in the experiments is sensitive to the axial component of
the scattered field, thus allowing us to obtain the amplitude and the phase of the local field. Our derivation brings out
new information, usually shaded when applied to an ensemble of particles. In particular, the dipole model widely used to describe
the scattered field by a spherical particle is not suitable to describe the three components of the scattered field in the
near zone. Our results are of interest for fundamental studies of the optical properties of single metal clusters and the
control of local phenomena such as enhancement, extinction, etc.
PACS 07.79.Fc; 78.67.Bf; 78.35.+c |
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