Search

Remote excitation and emission of two-photon luminescence and second-harmonic generation are observed in micrometer long gold rod optical antennas upon local illumination with a tightly focused near-infrared femtosecond laser beam. We show that the nonlinear radiations can be emitted from the entire antenna and the measured far-field angular patterns bear the information regarding the nature and origins of the respective nonlinear processes. We demonstrate that the nonlinear responses are transported by the propagating surface plasmon at excitation frequency, enabling thereby polariton-mediated tailoring and design of nonlinear responses., Comment: 6 pages, 4 figures

International audience; For their capability to localize and redirect electromagnetic field, metal nanoparticles have been recently viewed as efficient nanoantenna operating in the optical regime. In this article, we experimentally investigated the optical responses of coupled gold antenna pairs and measured the critical parameters defining antenna characteristics: resonant frequencies and bandwidths, detuning and gains, and radiation patterns.

International audience; We report on surface-plasmon propagation along coupled coplanar cavities periodically distributed in an otherwise unperturbed plasmonic crystal. We show that the dispersion of particular Bloch modes can exhibit multiple energy gaps that can be adjusted by choosing the cavity size. For resonant sizes, the composite crystals composed of juxtaposed cavities can support plasmon modes at frequencies within the gap of the unperturbed grating. In this case, we demonstrate that the surface-plasmon propagation relies on a hopping mechanism.

The excitation of surface plasmon polaritons in a thin metal film is extremely sensitive to the surrounding dielectric environment. We introduce here a far-field method to directly observe surface plasmon propagation and demonstrate that the lateral intensity decay length is affected by a change of the interface properties. The method relies on the detection of the intrinsic lossy modes associated with plasmon propagation in thin films. We also introduce a method to excite a broad spectral distribution of surface plasmons simultaneously throughout the visible spectrum allowing a unique form of surface plasmon-based spectroscopy.

A broad visible and infrared photoluminescence continuum is detected from surface-plasmon-enhanced transitions in gold nanostructures. We find that the ratio of generated infrared to visible emission is much stronger for gold nanostructures than for smooth gold films. While visible emission is well explained by interband transitions of d-band electrons into the conduction band and subsequent radiative recombination, the strong infrared emission cannot be accounted for by the same mechanism. We propose that the infrared emission is generated by intraband transitions mediated by the strongly confined fields near metal nanostructures (localized surface plasmons). These fields possess wave numbers that are comparable to the wave numbers of electrons in the metal, and the associated field gradients give rise to higher-order multipolar transitions. We compare photoluminescence spectra for single gold spheres, smooth and rough gold films, and sharp gold tips and demonstrate that the infrared signal is only present for surfaces with nanometer-scale roughness.

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.

Excitation and propagation of surface plasmons in silver films structured with narrow straight grooves were visualized in unprecedented detail by means of near-field optical techniques. Reflectivity, transmissivity, and scattering loss of the grooves are demonstrated. Their values are determined semiquantitatively. The surface plasmon attenuation are found to be dominated by material and surface/interface imperfections.