0000000000042486
AUTHOR
G. Colas Des Francs
showing 36 related works from this author
Surface-plasmon hopping along coupled coplanar cavities
2007
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.
Measuring the magnetic dipole transition of single nanorods by spectroscopy and Fourier microscopy
2020
International audience; Rare-earth doped nanocrystals possess optical transitions with significant either electric or magnetic dipole characters. They are of considerable interest for understanding and engineering light-matter interactions at the nanoscale with numerous applications in nanophotonics. Here, we study the 5 D 0 → 7 F 1 transition dipole vector in individual NaYF 4 : Eu 3+ nanorod crystals by Fourier and confocal micro-scopies. A single-crystal host matrix leads to narrow emission lines at room temperature that permit separation of the Stark sublevels resulting from the crystal-field splitting. We observe a fully magnetic transition and low variability of the transition dipole …
Leakage radiation microscopy of surface plasmon coupled emission: investigation of gain-assisted propagation in an integrated plasmonic waveguide.
2010
International audience; Using a single-mode dielectric-loaded surface plasmon polariton waveguide doped with quantum dots, we were able to slightly increase the propagation length of the mode by stimulated emission of plasmon. We analyse the amplification phenomenon in the visible range by combining leakage radiation microscopy and surface plasmon coupled emission techniques.
Spatiotemporal properties of nanoshell plasmonic response for strong-field experiments
2015
International audience; Field enhancement behavior of a SiO 2 /Au nanoshell is studied in the framework of strong-field physics. Localized plasmonic fields induce local electric field enhancement with the potential to lead to the strong-field regime without the use of costly amplified lasers. In this framework, electrons are tunnel ionized from the nanoshell and accelerated by the local field being spatially inhomogeneous in terms of spectral and polarization properties. These processes are happening within a single laser shot, and thermal effects are therefore neglected. We show that the localized response to ultrashort femtosecond pulses can be investigated by extending Mie theory to mult…
Differential method for modeling dielectric-loaded surface plasmon polariton waveguides
2008
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 stripe.
Submicrometer in-plane integrated surface plasmon cavities.
2007
International audience; The optical properties of in-plane integrated surface plasmon polariton (SPP) cavities comprised of a thin film area sandwiched between two one-dimensional Bragg SPP mirrors are investigated numerically and experimentally. We discuss the resonance condition of these cavities, and we analyze in details the physical origin of the dispersion of this resonance. On the basis of numerical results, we show that in-plane SPP cavities can be used to achieve local SPP field enhancement and antireflecting SPP layers. The numerical results are compared to near-field optical images recorded by operating a photon scanning tunneling microscope. From the near-field images recorded o…
Enhanced light confinement in a triangular aperture: Experimental evidence and numerical calculations
2005
We have recently demonstrated that the electric near-field emerging from a triangular aperture at the tip of a metal-coated tetrahedron of glass exhibits a highly confined and intense spot when the light incident from within the glass body is polarized perpendicularly to one edge of the aperture [Naber et al., Phys. Rev. Lett. 89, 210801 (2002)]. Here we present additional experimental material and a theoretical confirmation of this near-field optical effect. Based on the model of a triangular aperture in a planar metal film, we studied the influence of aperture size and film material on the field distribution. Even though our theoretical model is rather simplified as compared to the experi…
Optical gain, spontaneous and stimulated emission of surface plasmon polaritons in confined plasmonic waveguide
2010
International audience; We develop a theoretical model to compute the local density of states in a confined plasmonic waveguide. Based on this model, we derive a simple formula with a clear physical interpretation for the lifetime modification of emitters embedded in the waveguide. The gain distribution within the active medium is then computed following the formalism developed in a recent work [Phys. Rev. B 78, 161401 (2008)], by taking rigorously into account the pump irradiance and emitters lifetime modifications in the system. We finally apply this formalism to describe gain–assisted propagation in a dielectric–loaded surface plasmon polariton waveguide.
Photon antibunching in the optical near field
2010
International audience; We show that a combination of the field-susceptibility technique with the optical Bloch equations gives access to the temporal evolution of the populations and coherences of any quantum system placed in the optical near field of a nanostructure. In particular, we show that the near-field evanescent states, confined around dielectric or plasmonic particles, can be used to modify and control the photon statistics of the quantum system. This theoretical scheme leads to second-order autocorrelation functions in good agreement with recent experimental measurements performed with nitrogen-vacancy center in diamond nanocrystals placed in interaction with gold nanoparticles.
Electron-induced limitation of surface plasmon propagation in silver nanowires
2013
Plasmonic circuitry is considered as a promising solution-effective technology for miniaturizing and integrating the next generation of optical nano-devices. A key element is the shared metal network between electrical and optical information enabling an efficient hetero-integration of an electronic control layer and a plasmonic data link. Here, we investigate to what extend surface plasmons and current-carrying electrons interfere in such a shared circuitry. By synchronously recording surface plasmon propagation and electrical output characteristics of single chemically-synthesized silver nanowires we determine the limiting factors hindering the co-propagation of electrical current and sur…
Single-molecule controlled emission in planar plasmonic cavities
2014
International audience; We study the fluorescence emission from single dye molecules in coplanar plasmonic cavities composed of a thin gold film surrounded by two in-plane surface plasmon Bragg mirrors. We first discuss the effect of the presence of Bragg mirrors on the radiation diagram of surface plasmon coupled emission. Then, we investigate the role of the planar cavity size by single-molecule fluorescence lifetime imaging. Experimental data are compared to numerical simulations of the decay rates calculated as a function of the molecule orientation and position within the cavity. The creation of new decay channels by coupling to the cavity modes is also discussed. We measure a plasmoni…
SUBWAVELENGTH OPTICAL DEVICES FOR NANOMETER SCALE APPLICATIONS
2002
Recent progress in near-field optics instrumentation led to a new class of subwavelength optical experiments in which it is intended to use either the optical tunnel effect (OTE) or the lower mode based transmission (LMBT) in order to control the optical transfer between several delocalized detection or injection centers. This paper presents a panel of new theoretical and experimental results computed or observed near various dielectric or metallic patterns, linear, curved, or dashed, integrated in coplanar geometry. In particular, we demonstrate, how an efficient control of light evanescent waves can allow structures of subwavelength cross sections to be addressed.
Fluorescence relaxation in the near-field of a mesoscopic metallic particle : distance dependence and role of plasmon modes
2008
International audience; We analytically and numerically analyze the fluorescence decay rate of a quantum emitter placed in the vicinity of a spherical metallic particle of mesoscopic size (i.e with dimensions comparable to the emission wavelength). We discuss the efficiency of the radiative decay rate and non–radiative coupling to the particle as well as their distance dependence. The electromagnetic coupling mechanisms between the emitter and the particle are investigated by analyzing the role of the plasmon modes and their nature (dipole, multipole or interface mode). We demonstrate that near-field coupling can be expressed in a simple form verifying the optical theorem for each particle …
Dielectric-loaded surface plasmon polariton waveguides: Figures of merit and mode characterization by image and Fourier plane leakage microscopy
2008
International audience; Waveguiding of surface plasmon polaritons by dielectric-loaded metal structures is studied in detail by combining numerical simulations and leakage radiation microscopy. These types of waveguides are first numerically investigated using the effective index model and the differential method. We analyzed systematically the influence of the ridge width and thickness of the waveguide on the properties of the surface plasmon guided modes. In particular we investigated the confinement factor of the modes and their associated propagation lengths. These two parameters can be optimized by adjusting the thickness of the dielectric layer. Waveguides loaded with thick and thin d…
On the optimum form of an aperture for a confinement of the optically excited electric near field.
2008
Summary A triangular nanoaperture in an aluminium film was used previously as a probe in a scanning near-field optical microscope to image single fluorescent molecules with an optical resolution down to 30 nm. The high-resolution capability of the triangular aperture probe is because of a highly confined spot of the electric near field which emerges at an edge of the aperture, when the incident light is polarized perpendicular to this edge. Previous numerical calculations of the near-field distribution of a triangular aperture in a planar metal film using the field susceptibility technique yielded a nearly quantitative agreement with the experimental results. Using the same numerical techni…
A coupled lossy local-mode theory description of a plasmonic tip
2012
International audience; We investigate power propagation in a metal-coated tapered optical fiber. We analyze in detail the conversion from the fiber core guided mode to a surface plasmon polariton (SPP) confined at the tip apex. To this aim, we adapt coupled local-mode theory to include lossy modes. Two distinct regimes are identified. In the case of thin metal coating, a strong coupling regime occurs between a core guided mode and a SPP with good conversion efficiency. In the case of thick metal coating, a very weak coupling occurs. Finally, energy confinement and the role of Joule losses are discussed in the near-infrared and visible ranges. Moreover, the coupled equations derived for loc…
Purcell factor for a point-like dipolar emitter coupled to a two-dimensional plasmonic waveguide
2011
International audience; We theoretically investigate the spontaneous emission of a point-like dipolar emitter located near a two-dimensional plasmonic waveguide of arbitrary form. We invoke an explicit link with the density of modes of the waveguide describing the electromagnetic channels into which the emitter can couple. We obtain a closed form expression for the coupling to propagative plasmon, extending thus the Purcell factor to plasmonic configurations. Radiative and nonradiative contributions to the spontaneous emission are also discussed in detail.
Efficient surface plasmon field confinement in one-dimensional crystal line-defect waveguides
2006
International audience; The authors operate a near-field optical microscope to investigate surface plasmon polariton (SPP) propagation along linear waveguides opened into one-dimensional (1D) plasmonic crystals, i.e., crystals featuring a single lattice plane orientation. They show that efficient SPP field confinement can be achieved by this type of waveguide although no band gap exists in the direction perpendicular to the waveguide axis. From computed wave-vector diagrams, they show that 1D plasmonic crystals can open a wide range of prohibited propagation directions preventing from a significant coupling of the waveguide SPP modes with the crystal Bloch modes. Finally, the authors demons…
Single molecules probe local density of modes (LDOS) around photonic nanostructures
2008
International audience; According to Fermi's golden rule, the fluorescence decay rate is directly proportional to the projected local density of photonic modes (LDOS) at the molecule location. The relevant LDOS depends on the molecule orientation. In this paper, the direct measurement of the fluorescence lifetime near gold dot photonic structures is investigated and compared to calculated LDOS. Detailed analysis of the decay channels is presented on the basis of numerical simulations.
Quantum emitter states dressed by the plasmon modes of a metal nanoparticle in the strong coupling regim
2017
The quantum control of emitters is a key issue for quantum information processing at the nanoscale. This generally necessitates the strong coupling of emitters to a high Q-cavity for efficient manipulation of the atoms and field dynamics (cavity quantum electrodynamics or cQED). Since almost a decade, strong efforts are put to transpose cQED concepts to plasmonics in order to profit of the strong mode confinement of surface plasmons polaritons. Despite the intrinsic presence of lossy channels leading to strong decoherence in plasmonics systems, it has been experimentally proven that it is possible to reach the strong coupling regim [1].
High-resolution mapping of the optical near-field components at a triangular nano-aperture.
2009
A triangular nano-aperture in an aluminum film was used as a probe in a scanning near-field optical microscope (SNOM) to image single fluorescent molecules with an optical resolution down to 30 nm. The differently oriented molecules were employed as point detectors to map the vectorial components of the electric field distribution at the illuminated triangular aperture. The good agreement of the experimental results with numerical simulations enabled us to determine both the field map at a triangular aperture and the exact orientations of the probing molecules.
Surface plasmon interference excited by tightly focused laser beams
2007
International audience; We show that interfering surface plasmon polaritons can be excited with a focused laser beam at normal incidence to a plane metal film. No protrusions or holes are needed in this excitation scheme. Depending on the axial position of the focus, the intensity distribution on the metal surface is either dominated by interferences between counterpropagating plasmons or by a two-lobe pattern characteristic of localized surface plasmon excitation. Our experiments can be accurately explained by use of the angular spectrum representation and provide a simple means for locally exciting standing surface plasmon polaritons.
Resonance quality, radiative/ohmic losses and modal volume of Mie plasmons
2012
International audience; Molecular sytems are efficiently coupled to metal nanoparticles via the excitation of localized surface plasmons-polaritons (SPPs). The coupling strength between SPP and emitters can be estimated from the ratio Q/V where Q and V refer to the mode quality factor and effective volume, respectively. In this letter, we investigate in details the properties of Mie plasmons supported by a metallic nanosphere (Q-factor, radiative and ohmic losses, modal volume). We particularly focus on the difficulty to unambiguously define the modal volumes of localized SPPs. This leads us to propose two definitions; the first one is based on Purcell factor for a dipolar emitter in close …
Far-field imaging of the electromagnetic local density of optical states.
2008
International audience; We introduce a new experimental method to measure the local electromagnetic density of states (LDOS) by integrating the differential scattering cross section. The signal detected essentially reflects the intrinsic scattering response of the photonic structures and renders the partial LDOS dominated by evanescent modes. We give a theoretical understanding of the LDOS image formation and show a qualitative agreement between experimental images and theoretical maps. This approach can be practically applied to the direct measurement of an optical antenna's scattering efficiency and can provide valuable information for designing optimum structures utilized in radiative de…
Near-field coupling of a point-like dipolar source with a thin metallic film: Implication for STM plasmon excitations
2012
International audience; Recent experiments have shown that it is possible to excite surface plasmons on metallic films by injecting tunnel electrons from a sharp metal tip located in the immediate proximity of the sample. When working close to a bare metal film, the excitation of surface plasmons gives rise to typical circular patterns that can be recorded in both image and Fourier planes. Important physical parameters of surface plasmon propagation such as their propagation length can be extracted from these images. In this Letter, we discuss theoretically the physics of the plasmonic excitations induced by a STM tip.
Gain, detuning, and radiation patterns of nanoparticle optical antennas
2008
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.
SNOM signal near plasmonic nanostructures: an analogy with fluorescence decays channels
2008
International audience; Scanning Near-field Optical Microscope (SNOM) is based on local excitations of nanostructures deposited on a substrate (illumination mode). Ideally, the local source behaves like a dipolar emitter so that the SNOM signal is strongly similar to the fluorescence decay rates of an excited molecule that would be located at the SNOM tip position. We present here how the SNOM signal near plasmonic nanostructures can be used to analyze radiative and non-radiative contribution to the fluorescence decay rate.
Pre-determining the location of electromigrated gaps by nonlinear optical imaging
2014
In this paper we describe a nonlinear imaging method employed to spatially map the occurrence of constrictions occurring on an electrically-stressed gold nanowire. The approach consists at measuring the influence of a tightly focused ultrafast pulsed laser on the electronic transport in the nanowire. We found that structural defects distributed along the nanowire are efficient nonlinear optical sources of radiation and that the differential conductance is significantly decreased when the laser is incident on such electrically-induced morphological changes. This imaging technique is applied to pre-determined the location of the electrical failure before it occurs.
Dressed states of a quantum emitter strongly coupled to a metal nanoparticle
2016
Hybrid molecule-plasmonic nanostructures have demonstrated their potential for surface enhanced spectroscopies, sensing, or quantum control at the nanoscale. In this Letter, we investigate the strong coupling regime and explicitly describe the hybridization between the localized plasmons of a metal nanoparticle and the excited state of a quantum emitter, offering a simple and precise understanding of the energy exchange in full analogy with cavity quantum electrodynamics treatment and a dressed atom picture. Both near-field emission and far-field radiation are discussed, revealing the richness of such optical nanosources.
Subwavelength mapping of surface photonic states
2003
We show that the spectral tailoring of optical local density of states (LDOS) may be achieved by lithographically designed nanostructures and that the subwavelength mapping of the spectral variation of the optical LDOS is feasible by varying the driving frequency of the effective dipole used in an illumination mode scanning near-field optical microscope.
Electrical excitation of surface plasmons by an individual carbon nanotube transistor.
2013
We demonstrate here the realization of an integrated, electrically driven, source of surface plasmon polaritons. Light-emitting individual single-walled carbon nanotube field effect transistors were fabricated in a plasmonic-ready platform. The devices were operated at ambient conditions to act as an electroluminescence source localized near the contacting gold electrodes. We show that photon emission from the semiconducting channel can couple to propagating surface plasmons developing in the electrical terminals. Our results show that a common functional element can be operated for two different platforms emphasizing thus the high degree of compatibility between state-of-the-art nano-optoe…
Selective excitation of bright and dark plasmonic resonances of single gold nanorods.
2015
Plasmonic dark modes are pure near-field resonances since their dipole moments are vanishing in far field. These modes are particularly interesting to enhance nonlinear light-matter interaction at the nanometer scale because radiative losses are mitigated therefore increasing the intrinsic lifetime of the resonances. However, the excitation of dark modes by standard far field approaches is generally inefficient because the symmetry of the electromagnetic near-field distribution has a poor overlap with the excitation field. Here, we demonstrate the selective optical excitation of bright and dark plasmonic modes of single gold nanorods by spatial phase-shaping the excitation beam. Using two-p…
Polymer-metal waveguides characterization by Fourier plane leakage radiation microscopy
2007
International audience; The guiding properties of polymer waveguides on a thin gold film are investigated in the optical regime. The details of propagation in the waveguides are studied simultaneously in the object and Fourier planes, providing direct measurement of both the real and imaginary parts of the effective index of the guided mode. A fair agreement between theoretical analysis provided by the differential method and experimental leakage radiation microscopy data is shown. All these tools bring valuable information for designing and understanding such devices. (C) 2007 American Institute of Physics.
Imaging the Local Density of States of Optical Corrals
2002
International audience; This paper reports the experimental observation, at optical frequencies, of the electromagnetic local density of states established by nanostructures corresponding to the recently introduced concept of optical corral [G. Colas des Francs et al., Phys. Rev. Lett. 86, 4950 (2001)]. The images obtained by a scanning near-field optical microscope under specific operational conditions are found in agreement with the theoretical maps of the optical local density of states. A clear functionality of detection by the scanning near-field optical microscope is thereby identified since the theoretical maps are computed without including any specific tip model.
Metal enhanced fluorescence in rare earth doped plasmonic core–shell nanoparticles
2013
International audience; We theoretically and numerically investigate metal enhanced fluorescence of plasmonic core–shell nanoparticles doped with rare earth (RE) ions. Particle shape and size are engineered to maximize the average enhancement factor (AEF) of the overall doped shell. We show that the highest enhancement (11 in the visible and 7 in the near-infrared) is achieved by tuning either the dipolar or the quadrupolar particle resonance to the rare earth ion's excitation wavelength. Additionally, the calculated AEFs are compared to experimental data reported in the literature, obtained in similar conditions (plasmon mediated enhancement) or when a metal–RE energy transfer mechanism is…
Purcell factor for 3D- dipolar emitter coupling to 2D- plasmonic waveguides
2011
We theoretically investigate spontaneous emission of a quantum (3D) dipolar emitter located near a (2D) plasmonic waveguide of arbitrary form. The channels into which emitter couples (plasmon, scattering, electron-hole pairs creation) are well identified.