Hot carriers are energetic photoexcited carriers driving a large range of chemicophysical mechanisms. At the nanoscale, an efficient generation of these carriers is facilitated by illuminating plasmonic antennas. However, the ultrafast relaxation rate severally impedes their deployment in future hot-carrier based devices.
In this paper, we report on the picosecond relaxation dynamics of hot carriers in plasmonic monocrystalline gold nanoantennas. The ultrafast dynamics of the hot carriers is experimentally investigated by interrogating the nonlinear photoluminescence response of the antenna . From this investigation, we reveal some leverages to control the dynamics of such hot carriers within nano antenna. In particular, an increase by a factor up to five of this dynamics (from 0.5 ps to 2.5 ps) is observed for resonant nanoantenna compared to off-resonance antenna and when excitation power increases. By a two temperature model we model quantitatively the dynamics of hot carriers and we demonstrate the nonlinear generation of these carriers. The control over the carrier dynamics should allow to employ their energy more effieciently within physico-chemical processes.
In a second part, we investigate the hot carrier dynamics with a spectrally resolved two-pulse correlation configuration, and demonstrate that the relaxation of the photoexcited carriers depends of their energies relative to the Fermi level. We find a 60% variation in the relaxation rate for electron−hole pair energies ranging from ca. 0.2 to 1.8 eV. The quantitative relationship between hot-carrier energy and relaxation dynamics is an important finding for optimizing hot-carrier-assisted processes and shed new light on the intricacy of nonlinear photoluminescence in plasmonic .
 O. Demichel et al, ACS Photonics 3, 791 (2016)
 R. Méjard et al, ACS Photonics 3, 1482 (2016)
Electrically driven optical antennas are attracting much attention, in particular, due to necessity to develop integrated electrical source of surface plasmons for future plasmonic nanocircuitries. By default, this term denotes a metal nanostructure, in which electromagnetic oscillations at optical frequencies are excited by electrons, tunneling between metallic parts of the structure when a bias voltage is applied between them. Instead of relying on an inefficient inelastic light emission in a tunnel gap, we are suggesting to use ballistic nanoconstrictions as the feed element of an optical antennas in order to excite electromagnetic plasmonic modes. Similarly to tunneling structures, the voltage applied at the constriction falls over the contact of nanoscale length. Electron passing through the contact ballistically can gain the energy provided by the bias ~1eV and exchange it into an mode of the optical antenna. We discussed the underlying mechanisms responsible for the optical emission, and show that with nanoscale contact, one can reach quantum efficiency orders of magnitude larger than with standard tunneling structures.
This letter provides a brief summary on early work and developments on both controlling and studying the optical
properties of resonant metal nanoparticles and reports on all progress achieved since two years. Our approach is based on
controlled nanoscale photopolymerization triggered by local enhanced electromagnetic fields of silver nanoparticles
excited close to their dipolar plasmon resonance. By anisotropic polymerization, symmetry of the refractive index of the
surrounding medium was broken: C1v symmetry turned to C2v symmetry. This approach has overcome all the
difficulties faced by scanning probe methodologies to reproduce the form of the near field of the localized surface
plasmons and provides a new way to quantify its magnitude. Furthermore, this approach leads to the production of
polymer/metal hybrid nano-systems of new optical properties.
Waveguiding by dielectric-loaded surface plasmon-polaritons (DLSPP) structures are numerically and experimentally investigated. We used the effective index model to understand the influence of basic waveguide parameters such as width and thickness on the properties of the surface plasmon guided modes. A waveguide was fabricated
and experimentally studied. The effective indices of the modes supported by the waveguide and their propagation length are evaluated by leakage radiation microscopy in both the Fourier and imaging planes. Several excitation schemes were tested including surface plasmon coupling by diascopic or episcopic illumination as well as defectmediated excitation of guided modes. We found good agreement between theoretical values predicted by the effective index model and experimental values deduced from leakage radiation images.
In this paper we present an experimental apparatus capable of measuring the differential scattering cross sections of individual nanoparticles and arrangement of nanoparticles. We show that the mapping a partial differential scattering cross section, qualitative information about the electromagnetic local density of states dominated by evanescent modes scattered by the structure can be obtained.
The effect of field component perpendicular to the surface (longitudinal fields) on the photo-induced molecular
migration and surface deformations in azobenzene polymer films are investigated. Case of tip-enhanced near-field
illumination of the polymer surface is first discussed. In order to rule out the possible influence of mechanical
interaction between tip and polymer, tightly focused higher-order laser beams are then used. We demonstrate
that the surface topography is principally induced by longitudinal fields. Our findings can be explained by the
translational diffusion of isomerized chromophores when the constraining effect of the polymer-air interface is
Local surface plasmons resonances are widely accepted to be the basis for improving the efficiency of absorption and emission processes through a local electromagnetic field enhancement. Nonlinear processes in gold surfaces such as second harmonic generation or two-photon induced photoluminescence are particularly sensitive to this local effect due to their quadratic dependence on the intensity. Isolated regions of enhanced photoluminescence yield on rough gold surfaces were identified emphasizing the physical similarities with surface enhanced Raman scattering (SERS) substrates. 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 blue-shift of the photoluminescence peak wavelength with decreasing aspect ratio of the nanorods as well as an optically tuneable 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.
Plasmonics applications will benefit if reliable means to alter plasmon absorption and damping properties via external inputs are found. We are working towards this goal by functionalizing noble metal films with polarizable, excitonic molecular films. Examples include molecular j-aggregates, whose excitonic absorptions can be photobleached to modify plasmon absorption properties. We report two developments in this area. The first is the observation of coherent polarization coupling between the exciton of a molecular J-aggregate and the electronic polarization of noble metal nanoparticles. The second is a new far-field method to directly observe surface plasmon propagation, demonstrating that the lateral intensity decay length is affected by a change of the interface property. The method relies on the detection of the intrinsic lossy modes associated with plasmon propagation in thin films. We also uniquely introduce a method to excite a broad spectral distribution of surface plasmon simultaneously throughout the visible spectrum allowing surface plasmon based spectroscopy to be performed.
The surface plasmons of metal films and nanostructures are increasingly well-known for applications in sensor technologies and photonics applications. Their potential is largely due to the plasmons' characteristic as an interface phenomenon and the generation of an optical near-field at the interface. In many cases, the spatial dimensions of the near-field lie significantly below the diffraction limit of conventional optics in at least one dimension. This requires novel methods means for imaging their spatial profile and propagation properties. We present recent methods ongoing in our laboratory for imaging plasmonic features of metal nanostructures
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 surface plasmons with an area much smaller than their lateral decay length. We visualize directly the intensity distribution of the surface plasmons by detecting the intrinsic lossy modes associated with plasmon propagation in thin films. Our approach allowed us to excite simultaneously a broad spectral continuum of surface waves and to describe for the first time surface plasmon rainbow jets. We quantified the attenuation of the jet as a function of wavelength and film thickness and compared it to the different propagation damping mechanisms. We demonstrated the influence of the interface on the surface plasmon propagation length and demonstrated surface plasmon spectral filtering using molecular excitonic adsorbates.