0000000000862712
AUTHOR
Gérard Colas Des Francs
showing 33 related works from this author
Generalized bloch equations for optical interactions in confined geometries
2005
By combining the field-susceptibility technique with the optical Bloch equations, a general formalism is developed for the investigation of molecular photophysical phenomena triggered by nanometer scale optical fields in the presence of complex environments. This formalism illustrate the influence of the illumination regime on the fluorescence signal emitted by a single molecule in a complex environment. In the saturated case, this signal is proportional to the optical local density of states, while it is proportional to the near-field intensity in the non-saturated case. (C) 2005 Elsevier B.V. All rights reserved.
Nonlinear photon-assisted tunneling transport in optical gap antennas.
2014
International audience; We introduce strongly coupled optical gap antennas to interface optical radiation with current-carrying electrons at the nanoscale. The transducer relies on the nonlinear optical and electrical properties of an optical gap antenna operating in the tunneling regime. We discuss the underlying physical mechanisms controlling the conversion involving d-band electrons and demonstrate that a simple two-wire optical antenna can provide advanced optoelectronic functionalities beyond tailoring the electromagnetic response of a single emitter. Interfacing an electronic command layer with a nanoscale optical device may thus be facilitated by the optical rectennas discussed here.
Relationship between scanning near-field optical images and local density of photonic states
2001
From numerical calculations based on Green's dyadic formalism, we show that a scanning near-field optical microscope (SNOM) working with a point-like illuminating probe delivers images that contain features directly related to the local density of photonic states (LDOS). More precisely, an unambiguous identification of the partial LDOSs (x, y or z polarized) can be made in the SNOM images when the solid angle of detection reaches 2π sr.
Molecular quenching and relaxation in a plasmonic tunable system
2008
Molecular fluorescence decay is significantly modified when the emitting molecule is located near a plasmonic structure. When the lateral sizes of such structures are reduced to nanometer-scale cross sections, they can be used to accurately control and amplify the emission rate. In this Rapid Communication, we extend Green's dyadic method to quantitatively investigate both radiative and nonradiative decay channels experienced by a single fluorescent molecule confined in an adjustable dielectric-metal nanogap. The technique produces data in excellent agreement with current experimental work.
Delocalization of Nonlinear Optical Responses in Plasmonic Nanoantennas
2015
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.
Determinant role of the edges in defining surface plasmon propagation in stripe waveguides and tapered concentrators
2012
International audience; In this paper, we experimentally show the effect of waveguide discontinuity on the propagation of the surface plasmon in metal stripes and tapered terminations. Dual-plane leakage microscopy and near-field microscopy were performed on Au stripes with varied widths to imag29e the surface plasmon intensity distribution in real and reciprocal spaces. We unambiguously demonstrate that edge diffraction is the limiting process determining the cutoff conditions of the surface plasmon mode. Finally, we determine the optimal tapered geometry leading to the highest transmission.
Measuring the differential scattering cross-section of gold nanoparticles - art. no. 70321E
2008
International audience; 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.
Evaluating plasmonic transport in current-carrying silver nanowires
2013
cited By 1; International audience; Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support1,2,3. In this context, metal nanowires are especially desirable for realizing dense routing networks4. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons5 in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires6 randomly distributed on a glass substrate7. The positions of the nanowire ends …
Near-field properties of plasmonic nanostructures with high aspect ratio
2014
International audience; Using the Green's dyad technique based on cuboidal meshing, we compute the electromagnetic field scattered by metal nanorods with high aspect ratio. We investigate the effect of the meshing shape on the numerical simulations. We observe that discretizing the object with cells with aspect ratios similar to the object's aspect ratio improves the computations, without degrading the convergency. We also compare our numerical simulations to finite element method and discuss further possible improvements.
Theory of Near‐field Optical Imaging with a Single Molecule as Light Source
2002
Scanning near-field optical microscopes (SNOM) illuminate a sample in the very near-field using a nanometer sized tip. Ideally, the light source should be point-like and many efforts have been made to optimize tip efficiency (see, for example, the article of Heimel et al in this issue). Very recently, Sandoghdar et al have realized a molecular probe tip in which a terrylene molecule inserted in a paraterphenyl microcrystal is attached at the extremity of the probe tip [1]. The excited molecule behaves as a point-like light source which is raster scanned over an aluminium patterned structure. We propose here an analysis of this experiment based on the field-susceptibility formalism (also cal…
Manipulating and squeezing the photon local density of states with plasmonic nanoparticle networks
2010
International audience; In this Brief Report, we show that when interconnected networks of gold particles are deposited onto a clean planar surface, they strongly modify the photonic local density of states LDOS in the immediate proximity of the self-assembled nanoparticles. They represent unique architectures for the subwavelength patterning of initially flat photonic LDOS. Moreover, we show that their local spectral signatures are well suited for the generation of sites able to enhance molecular fluorescence intensity.
Imaging Surface Plasmons
2012
Controlling surface plasmons is at the heart of plasmonics. Advances in this field are to a large extent triggered by our ability to visualize surface plasmons in their different forms. In this chapter, we provide a review of the different techniques capable of imaging and visualizing surface plasmons. We have divided these techniques in three distinct families: proximal probe techniques, far-field microscopies, and electron imaging. We review here their principal characteristics, advantages, and limitations and illustrate the discussion with images taken from the literature.
Effect of quantized conductivity on the anomalous photon emission radiated from atomic-size point contacts
2019
We observe anomalous visible to near-infrared electromagnetic radiation emitted from electrically driven atomic-size point contacts. We show that the number of photons released strongly depends on the quantized conductance steps of the contact. Counter-intuitively, the light intensity features an exponential decay dependence with the injected electrical power. We propose an analytical model for the light emission considering an out-of-equilibrium electron distribution. We treat photon emission as bremsstrahlung process resulting from hot electrons colliding with the metal boundary and a find qualitative accord with the experimental data.
Two-Color Single Hybrid Plasmonic Nanoemitters with Real Time Switchable Dominant Emission Wavelength
2015
International audience; We demonstrate two-color nanoemitters that enable the selection of the dominant emitting wavelength by varying the polarization of excitation light. The nanoemitters were fabricated via surface plasmon-triggered two-photon polymerization. By using two polymerizable solutions with different quantum dots, emitters of different colors can be positioned selectively in different orientations in the close vicinity of the metal nanoparticles. The dominant emission wavelength of the metal/polymer anisotropic hybrid nanoemitter thus can be selected by altering the incident polarization.
Electrostatic Control over Optically Pumped Hot Electrons in Optical Gap Antennas
2020
International audience; We investigate the influence of a static electric field on the incoherent nonlinear response of an unloaded electrically contacted nanoscale optical gap antenna. Upon excitation by a tightly focused near-infrared femtosecond laser beam, a transient elevated temperature of the electronic distribution results in a broadband emission of nonlinear photoluminescence (N-PL). We demonstrate a modulation of the yield at which driving photons are frequency up-converted by means of an external control of the electronic surface charge density. We show that the electron temperature and consequently the N-PL intensity can be enhanced or reduced depending on the command polarity a…
Strongly directional scattering from dielectric nanowires
2017
It has been experimentally demonstrated only recently that a simultaneous excitation of interfering electric and magnetic resonances can lead to uni-directional scattering of visible light in zero-dimensional dielectric nanoparticles. We show both theoretically and experimentally, that strongly anisotropic scattering also occurs in individual dielectric nanowires. The effect occurs even under either pure transverse electric or pure transverse magnetic polarized normal illumination. This allows for instance to toggle the scattering direction by a simple rotation of the incident polarization. Finally, we demonstrate that directional scattering is not limited to cylindrical cross-sections, but…
Optical analogy to electronic quantum corrals.
2000
We describe full multiple-scattering calculations of localized surface photonic states set up by lithographically designed nanostructures made of a finite number of dielectric pads deposited on a planar surface. The method is based on a numerical solution of the dyadic Dyson's equation. When the pads are arranged to form a closed circle, we find field patterns that look like the electronic charge density recently observed above quantum corrals. We propose two experimental techniques that could be used to observe these electromagnetic modes in direct space.
Quantum plasmonics with multi-emitters: application to stimulated Raman adiabatic passage
2018
We construct a mode-selective effective model describing the interaction of the localised surface plasmon polaritons (LSPs) supported by a spherical metal nanoparticle (MNP) with N quantum emitters (QEs) in an arbitrary geometric arrangement. Simplifying previously presented procedures, we develop a formulation in which the field response in the presence of the MNP can be decomposed into orthogonal modes, expanding the Green tensor of the system in the spherical vector harmonics basis and using the generalized global Löwdin orthogonalization algorithm. We investigate the possibility of using the LSPs as mediators of an efficient control of population transfer between two QEs. We show that a…
Fano-resonances in High Index Dielectric Nanowires for Directional Scattering
2018
High refractive index dielectric nanostructures provide original optical properties thanks to the occurrence of size- and shape-dependent optical resonance modes. These modes commonly present a spectral overlap of broad, low-order modes (\textit{e.g}. dipolar modes) and much narrower, higher-order modes. The latter are usually characterized by a rapidly varying frequency-dependent phase, which - in superposition with the lower order mode of approximately constant phase - leads to typical spectral features known as Fano resonances. Interestingly, such Fano resonances occur in dielectric nanostructures of the simplest shapes. In spheroidal nanoparticles, interference between broad magnetic di…
Sorting of Single Biomolecules based on Fourier Polar Representation of Surface Enhanced Raman Spectra
2016
AbstractSurface enhanced Raman scattering (SERS) spectroscopy becomes increasingly used in biosensors for its capacity to detect and identify single molecules. In practice, a large number of SERS spectra are acquired and reliable ranking methods are thus essential for analysing all these data. Supervised classification strategies, which are the most effective methods, are usually applied but they require pre-determined models or classes. In this work, we propose to sort SERS spectra in unknown groups with an alternative strategy called Fourier polar representation. This non-fitting method based on simple Fourier sine and cosine transforms produces a fast and graphical representation for sor…
Discerning the Origins of the Amplitude Fluctuations in Dynamic Raman Nanospectroscopy
2012
International audience; We introduce a novel experimental and analytical method for discerning rare surface-enhanced Raman scattering (SERS) events observable at the nanoscale. We show that the kinetics of the Raman activity recorded on an isolated nanostructure is punctuated by intense and rare events of large amplitude and spectral variations. The fluctuations of thousands of SERS spectra were analyzed statistically in terms of power density functions, and the occurrence of the rare events was quantified by a wavenumber statistics. Our analysis enables one to extract valuable and unique spectroscopic signature of Raman variations usually hidden in time-average or space-average measurement…
Silencing and enhancement of second-harmonic generation in optical gap antennas
2012
International audience; Amplifying local electromagnetic fields by engineering optical interactions between individual constituents of an optical antenna is considered fundamental for efficient nonlinear wavelength conversion in nanometer-scale devices. In contrast to this general statement we show that high field enhancement does not necessarily lead to an optimized nonlinear activity. In particular, we demonstrate that second-harmonic responses generated at strongly interacting optical gap antennas can be significantly suppressed. Numerical simulations are confirming silencing of second-harmonic in these coupled systems despite the existence of local field amplification. We then propose a…
Excitation of a one-dimensional evanescent wave by conical edge diffraction of surface plasmon
2011
International audience; The experimental observation of a one-dimensional evanescent wave supported by a 90◦ metal edge is reported. Through a measurement of in-plane momenta, we clearly demonstrate the dimensional character of this surface wave and show that it is non-radiative in the superstrate. Excitation conditions, lateral extension and polarization properties of this wave are discussed. Finally, we explore the effect of the surrounding dielectric medium and demonstrate that a single edge can sustain distinct excitations.
Modal and wavelength conversions in plasmonic nanowires
2021
We show that plasmonic nanowire-nanoparticle systems can perform nonlinear wavelength and modal conversions and potentially serve as building blocks for signal multiplexing and novel trafficking modalities. When a surface plasmon excited by a pulsed laser beam propagates in a nanowire, it generates a localized broadband nonlinear continuum at the nanowire surface as well as at active locations defined by sites where nanoparticles are absorbed (enhancement sites). The local response may couple to new sets of propagating modes enabling a complex routing of optical signals through modal and spectral conversions. Different aspects influencing the optical signal conversions are presented, includ…
Differential method for modelling dielectric-loaded surface plasmon polariton waveguides
2008
International audience; This paper demonstrates the efficiency of the differential method, a conventional grating theory, to investigate dielectric loaded surface plasmon polariton waveguides (DLSPPWs), known to be a potential solution for optical interconnects. The method is used to obtain the mode effective indices (both real and imaginary parts) and the mode profiles. The results obtained with the differential method are found to be in good agreement with those provided by the effective index method or finite elements. The versatility of the differential method is demonstrated by considering complex configurations such as trapezoidal waveguides or DLSPPWs lying on a finite width metal st…
Modelling resonant coupling between microring resonators addressed by optical evanescent waves
2004
In this paper we study the properties of microring resonator structures fabricated with high-index-of-refraction dielectric material. These structures concentrate light and can produce very strong optical potential gradients. They are of great interest for the trapping, manipulation and transport of cold atoms near surfaces. The study consists of two parts: in the first part we investigate the symmetry properties of the resonator response for simple models of the microring structures. In the second part we present detailed numerical calculations of the actual spectra for realistic microfabricated structures. We employ the direct space integral equation method (DSIEM). This method, based on …
Coupling of a dipolar emitter into one-dimensional surface plasmon.
2013
Quantum plasmonics relies on a new paradigm for light-matter interaction. It benefits from strong confinement of surface plasmon polaritons (SPP) that ensures efficient coupling at a deep subwavelength scale, instead of working with a long lifetime cavity polariton that increases the duration of interaction. The large bandwidth and the strong confinement of one dimensional SPP enable controlled manipulation of a nearby quantum emitter. This paves the way to ultrafast nanooptical devices. However, the large SPP bandwidth originates from strong losses so that a clear understanding of the coupling process is needed. In this report, we investigate in details the coupling between a single emitte…
Spatial Distribution of the Nonlinear Photoluminescence in Au Nanowires
2019
When gold nanowires are excited with a tightly focused femtosecond laser a distributed nonlinear photoluminescence (N-PL) develops throughout the entire structure. A complete spaced-resolved analysis of the spectral signature of the nanowire nonlinear response is carried out to understand the origin of the distributed nonlinear response. We discuss various mechanisms to explain the experimental data and unambiguously demonstrate that the spatial and spectral extension of the N-PL in the nanowire are mainly dictated by the propagation of a surface plasmon excited at the pump wavelength. We also present experimental signature of near-field excitation of a broadband continuum of surface plasmo…
Surface plasmon routing in dielectric-loaded surface plasmon polariton waveguides - art. no. 70330S
2008
International audience; 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 defect-mediated …
Dipolar and quadrupolar plasmon LASER modes for core-shell
2012
International audience; Spasers are based on a combination of the localized plasmon field properties of the metallic material with an amplification medium [1]. The optical properties of these compound systems are based on a compensation of the metallic losses trough the optical gain of the amplification medium. Recently it was demonstrated experimentally that coating a gold nanoparticle with a silica shell containing Oregon Green 488 allows to overcome the loss-of-surface plasmon resonance [2]. One of the consequences of the compensation of the losses is an extremely large enhancement of the local field amplitudes (giant resonances). Rising the gain leads to a singularity stricking the tran…
PLASMONIQUE MOLÉCULAIRE : SPECTROSCOPIE SUR SURFACE MÉTALLIQUE ET MATÉRIAUX HYBRIDES POUR LA PHOTONIQUE INTÉGRÉE
2009
Ce document synthétise mes travaux de recherches sur la période 2002-2009. Les axes majeurs de mon activité portent sur le couplage de molécules avec des particules métalliques, supportant des modes plasmons (SPP) : - Microscopie et spectroscopie optiques en champ proche, - Relaxation moléculaire par couplage aux plasmons, en particulier, la possibilité de modifier les propriétés d'émission de molécules par couplage avec des structures métalliques, – Composants plasmoniques pour la photonique intégrée, où, à l'inverse, l'ingéniérie de matériaux optiques (polymères dop´es, non linéaire, . . .) permet de contrôler la propagation de SPPs le long de films métalliques. Finalement, je démontrerai…
Two-color nanoemiter
2015
International audience
Two-color hybrid nano-emitters
2015
International audience