Biomedical subjects

A Bouhelier

Publications and source records attributed to A Bouhelier.

7 recordsLinked to original sources

PubMed2005

Surface plasmon characteristics of tunable photoluminescence in single gold nanorods.

Light emission resulting from two-photon excited gold nanoparticles has been proposed to originate from the radiative decay of surface plasmon resonances. In this vein, we investigated luminescence from individual gold nanorods and found that their emission characteristics closely resemble surface plasmon behavior. In particular, we observed spectral similarities between the scattering spectra of individual nanorods and their photoluminescence emission. We also measured a blueshift of the photoluminescence peak wavelength with decreasing aspect ratio of the nanorods as well as an optically tunable shape-dependent spectrum of the photoluminescence. The emission yield of single nanorods strongly depends on the orientation of the incident polarization consistent with the properties of surface plasmons.

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PubMed2005

Surface plasmon rainbow jets.

A new method for optically exciting and visualizing surface plasmons in thin metal films is described. The technique relies on the use of a high-numerical-aperture objective lens to locally launch a broad wavelength spectrum of surface waves and to detect the leaky radiative modes associated with them. We used this approach to obtain a direct visualization of the plasmon intensity distributions, e.g., rainbow jets, and to quantify their propagation lengths throughout the visible spectrum.

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PubMed2004

Applications of field-enhanced near-field optical microscopy.

Metal nanostructures such as sharp tips can enhance emission yields through shape-induced local field enhancement. The enhancement originates from two mechanisms: surface plasmons and electrostatic lightening rod effects. We present fluorescence imaging using the strong local field created at the apex of a gold tip and demonstrate optical resolution of 25 nm. The enhancement effect gives also rise to photoemission from the tip itself. Measured spectra of the tip emission show a broad band continuum together with a second-harmonic peak. Both continuum and second-harmonic are confined at the apex of the tip. We find that, depending on the spectral position, the photoluminescence originates either from intraband or from interband transitions. The nonlinear response can be described by a single dipole oscillating at the second-harmonic frequency and oriented along the tip axis. These unique properties can be used to map focal fields distributions.

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PubMed2003

Near-field second-harmonic generation induced by local field enhancement.

The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally verified by imaging the spatial field distribution of strongly focused laser modes.

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PubMed2003

Plasmon-coupled tip-enhanced near-field optical microscopy.

Near the cut-off radius of a guided waveguide mode of a metal-coated glass fibre tip it is possible to couple radiation to surface plasmons propagating on the outside surface of the metal coating. These surface plasmons converge toward the apex of the tip and interfere constructively for particular polarization states of the initial waveguide mode. Calculations show that a radially polarized waveguide mode can create a strong field enhancement localized at the apex of the tip. The highly localized enhanced field forms a nanoscale optical near-field source.

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PubMed2001

Propagation and diffraction of locally excited surface plasmons.

With the use of optical near-field techniques, it is now possible to excite or observe surface plasmons with high lateral resolution. A theoretical study is presented of surface plasmon excitation by near-field optical probes and the influence of well-defined structures on surface plasmon propagation and surface plasmon detection in the far field. The generation and the diffraction of the surface plasmon is calculated by using a theoretical scheme founded upon a first-order perturbation expansion of the Rayleigh-Fano method. A very good agreement is obtained between numerical and experimental results. The theoretical tools used should prove a useful guideline for future experiments of nanooptics with surface plasmons.

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PubMedDate not supplied

Plasmon transmissivity and reflectivity of narrow grooves in a silver film.

Surface plasmon (SP) reflectivity and transmissivity of narrow grooves in silver films are studied. The SP source is the probe of a scanning near-field optical microscope. Locally detected leakage radiation from the SP provides detailed information on the paths of SP propagation, in particular the influence of perturbations. Global detection provides representative average data on the SP properties of a given metal film and its structures. A groove of 200 nm width, for instance, reflects/transmits about 15%/80% of 'blue-green' SP radiation at normal incidence.

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