Showing papers by "Olivier J. F. Martin published in 2013"
TL;DR: It is demonstrated theoretically and experimentally that Fano resonances can be obtained by destructive interference between two bright dipolar modes out of phase and a simple oscillator model is provided to predict and fit the far-field scattering.
Abstract: Fano resonances in hybridized systems formed from the interaction of bright modes only are reported. Despite precedent works, we demonstrate theoretically and experimentally that Fano resonances can be obtained by destructive interference between two bright dipolar modes out of phase. A simple oscillator model is provided to predict and fit the far-field scattering. The predictions are verified with numerical calculations using a surface integral equation method for a wide range of geometrical parameters. The validity of the model is then further demonstrated with experimental dark-field scattering measurements on actual nanostructures in the visible range. A remarkable set of properties like crossings, avoided crossings, inversion of subradiant and superradiant modes and a plasmonic equivalent of a bound state in the continuum are presented. The nanostructure, that takes advantage of the combination of Fano resonance and nanogap effects, also shows high tunability and strong near-field enhancement. Our s...
318 citations
TL;DR: These results illustrate the versatility of Fano resonant structures to engineer specific optical responses both in the linear and nonlinear regimes thus paving the way for future investigations on the role of dark modes in nonlinear and quantum optics.
Abstract: Significant augmentation of second harmonic generation using Fano resonances in plasmonic heptamers made of silver is theoretically and experimentally demonstrated. The geometry is engineered to simultaneously produce a Fano resonance at the fundamental wavelength, resulting in a strong localization of the fundamental field close to the system, and a higher order scattering peak at the second harmonic wavelength. These results illustrate the versatility of Fano resonant structures to engineer specific optical responses both in the linear and nonlinear regimes thus paving the way for future investigations on the role of dark modes in nonlinear and quantum optics.
210 citations
TL;DR: It is theoretically and experimentally demonstrated that the radiance of a plasmonic mode can be classified into three different regimes, and it is shown that geometrical displacements and deformations at the Ångström scale can be detected optically by measuring theRadiance.
Abstract: Plasmonic modes with long radiative lifetimes combine strong nanoscale light confinement with a narrow spectral line width carrying the signature of Fano resonances, making them very promising for nanophotonic applications such as sensing, lasing, and switching. Their coupling to incident radiation, also known as radiance, determines their optical properties and optimal use in applications. In this work, we theoretically and experimentally demonstrate that the radiance of a plasmonic mode can be classified into three different regimes. In the weak coupling regime, the line shape exhibits remarkable sensitivity to the dielectric environment. We show that geometrical displacements and deformations at the Angstrom scale can be detected optically by measuring the radiance. In the intermediate regime, the electromagnetic energy stored in the mode is maximal, with large electric field enhancements that can be exploited in surface enhanced spectroscopy applications. In the strong coupling regime, the interaction can result in hybridized modes with tunable energies.
117 citations
TL;DR: This study paves the way toward sensitive nanoscale biochemical sensors and immunoassays with a low limit of detection and, in general, any nano-optical device where Ohmic losses limit the performance.
Abstract: Plasmonic modes with long radiative lifetimes, subradiant modes, combine strong confinement of the electromagnetic energy at the nanoscale with a steep spectral dispersion, which makes them promising for biochemical sensors or immunoassays. Subradiant modes have three decay channels: Ohmic losses, their extrinsic coupling to radiation, and possibly their intrinsic dipole moment. In this work, the performance of subradiant modes for refractive index sensing is studied with a general analytical and numerical approach. We introduce a model for the impact that has different decay channels of subradiant modes on the spectral resolution and contrast. It is shown analytically and verified numerically that there exists an optimal value of the mode coupling for which the spectral dispersion of the resonance line shape is maximal. The intrinsic width of subradiant modes determines the value of the dispersion maximum and depends on the penetration of the electric field in the metallic nanostructure. A figure of merit, given by the ratio of the sensitivity to the intrinsic width, which are both intrinsic properties of subradiant modes, is introduced. This figure of merit can be directly calculated from the line shape in the far-field optical spectrum and accounts for the fact that both the spectral resolution and contrast determine the limit of detection. An expression for the intrinsic width of a plasmonic mode is derived and calculated from the line shape parameters and using perturbation theory. The method of analysis introduced in this work is illustrated for dolmen and heptamer nanostructures. Fano-resonant systems have the potential to act as very efficient refractive index sensing platforms compared to Lorentz-resonant systems, due to control of their radiative losses. This study paves the way toward sensitive nanoscale biochemical sensors and immunoassays with a low limit of detection and, in general, any nano-optical device where Ohmic losses limit the performance.
98 citations
TL;DR: Interestingly, minute geometry asymmetry and surface roughness are clearly revealed by far-field analysis, demonstrating that second harmonic generation is a promising tool for the sensitive optical characterization of plasmonic nanostructures.
Abstract: Second harmonic generation from plasmonic nanoantennas is investigated numerically using a surface integral formulation for the calculation of both the fundamental and the second harmonic electric field. The comparison between a realistic and an idealized gold nanoantenna shows that second harmonic generation is extremely sensitive to asymmetry in the nanostructure shape even in cases where the linear response is barely modified. Interestingly, minute geometry asymmetry and surface roughness are clearly revealed by far-field analysis, demonstrating that second harmonic generation is a promising tool for the sensitive optical characterization of plasmonic nanostructures. Furthermore, defects located where the linear field is strong (e.g., in the antenna gap) do not necessarily have the strongest impact on the second harmonic signal.
91 citations
TL;DR: In this article, the authors studied the dependence of the geometrical parameters such as layer thickness and shape on the near-field of localized plasmon resonances for traditional adhesion layers such as Cr, Ti, and h02.
Abstract: Adhesion layers, required to stabilize metallic nanostngtures, dramatically deteriorate the performances of plasmonic sensors, by severely damping the plasmon modes. In this article, we show that these detrimental effects critically depend on the overlap of the electromagnetic near-field of the resonant plasmon mode with the adhesion layer and can be minimized by careful engineering of the latter. We study the dependence of the geometrical parameters such as layer thickness and shape on the near-field of localized plasmon resonances for traditional adhesion layers such as Cr, Ti, and h02. Our experiments and simulations reveal a strong dependence of the damping on the layer thickness, in agreement with the exponential decay of the piasmon near-field. We developed a method to minimize the damping by selective deposition of thin adhesion layers (<1 nm) In a manner that prevents the layer to overlap with the hotspots of the plasmonlc structure. Such a designed structure enables the use of standard Cr and Ti adhesion materials to fabricate robust plasmonic sensors without deteriorating their sensitivity.
86 citations
TL;DR: This work demonstrates an attractive alternative based on Fabry-Perot type nanogap resonators, where the resonance is defined by the gap width and vertical elongation instead of the particle geometry, to produce maximum near-field enhancement for surface-enhanced Raman scattering.
Abstract: Pairs of metal nanoparticles with a sub-10 nm gap are an efficient way to achieve extreme near-field enhancement for sensing applications. We demonstrate an attractive alternative based on Fabry–Perot type nanogap resonators, where the resonance is defined by the gap width and vertical elongation instead of the particle geometry. We discuss the crucial design parameters for such gap plasmons to produce maximum near-field enhancement for surface-enhanced Raman scattering and show compatibility of the pattern processing with low-cost and low-resolution lithography. We find a minimum critical metal thickness of 80 nm and observe that the mode coupling from the far field increases by tapering the gap opening. We also show the saturation of the Raman signal for nanogap periodicities below 1 μm, demonstrating efficient funneling of light into such nanogap arrays.
82 citations
TL;DR: A surface integral formulation for the second-harmonic generation (SHG) from periodic metallic-dielectric nanostructures is described in this article, which requires the discretization of the scatterers' surface in the unit cell only.
Abstract: A surface integral formulation for the second-harmonic generation (SHG) from periodic metallic–dielectric nanostructures is described. This method requires the discretization of the scatterers’ surface in the unit cell only. All the physical quantities involved in this problem are derived in the unit cell by applying specific periodic boundary conditions both at the fundamental and the second-harmonic (SH) frequencies. Both the fundamental and the SH electric fields are computed using the method of moments and periodic Green’s function evaluated with the Ewald’s method. The accuracy of the method is carefully assessed using two specific cases, namely the surface plasmon enhancement of SHG from a gold film and the SHG from L-shaped nanoparticle arrays. These two examples emphasize the accuracy and versatility of the proposed method, which can be applied to a broad range of periodic metallic structures, including plasmonic arrays on arbitrary substrates and metamaterials.
53 citations
TL;DR: A novel third generation biosensor was developed based on one-shot adsorption of chemically-modified cytochrome c (cyt c) onto bare gold electrodes and was able to perform real-time and non-invasive detection of endogeneous H₂O₁ released by unicellular aquatic microorganisms, Chlamydomonas reinhardtii, upon cadmium exposure.
46 citations
TL;DR: The simulations show that both scattering behaviour and polarisation charge distribution depend significantly on rounding, which suggests that it is important to incorporate the effect of rounding to be able to design plasmonic nanostructures with desired properties.
Abstract: We study the effect of realistically rounding nanorod antennae and gap antennae on their far field and near field properties. The simulations show that both scattering behaviour and polarisation charge distribution depend significantly on rounding. Rounding is also seen to have a major effect on coupling between nanostructures. The results suggest that it is important to incorporate the effect of rounding to be able to design plasmonic nanostructures with desired properties.
44 citations
TL;DR: In this article, the authors proposed reusable surface-enhanced Raman scattering (SERS) substrates for analytical applications or for comparative measurements to enable the distinction between electromagnetic and chemical enhancement.
Abstract: Surface-enhanced Raman scattering (SERS) has become increasingly popular in the scientific and industrial communities because ofits analyticalcapabilities and potential tostudy fundamentalsinplasmonics.Although undercertainconditionsextremely high sensitivity is possible, the practical use of SERS is frequently limited by instability and poor reproducibility of the enhancement factor. For analytical applications or for comparative measurements to enable the distinction between electromagnetic and chemical enhancement, the development of standardized and recyclable SERS substrates, having uniform and persistent performance, is proposed. To this end, we have fabricated periodic nanoslit arrays using extreme ultraviolet lithography that provide average large (2*10 6 ) and homogeneous SERS enhancement factors with a spot-to-spot variability of less than 3%. In addition, they are reusable without any degradation or loss of enhancement. The fabrication of such arrays consists of two steps only, lithographic patterning followed by metal evaporation. Both processes may be performed over areas of several square mm on any planar substrate. The sensor capabilities were demonstrated by substrates with monomolecular films of several different thiols. The concept of reusable SERS substrates may open a powerful platform within an analytical tool and in particular for systematic SERS studies for the investigation of fundamental parameters such as chemical enhancement, surface selection rules, and molecular alignment. Copyright © 2012 John Wiley & Sons, Ltd. Supporting information may be found in the online version of this article.
TL;DR: Design rules for nano antennas are developed which enable the generation of circular polarized light via the excitation of circular plasmonic modes in the structure by modifying this coupling strength from a weak to a strong regime to control the helicity of the scattered field.
Abstract: The far-field polarization of the optical response of a plasmonic antenna can be tuned by subtly engineering of its geometry. In this paper, we develop design rules for nano antennas which enable the generation of circular polarized light via the excitation of circular plasmonic modes in the structure. Two initially orthogonal plasmonic modes are coupled in such a way that a rotational current is excited in the structure. Modifying this coupling strength from a weak to a strong regime controls the helicity of the scattered field. Finally, we introduce an original sensing approach that relies on the rotation of the incident polarization and demonstrates a sensitivity of 0.23 deg·nm–1 or 33 deg·RIU–1, related to changes of mechanical dimensions and the refractive index, respectively.
TL;DR: It is found that these LSP-SPP interactions are not limited to small particles, but that they are present as well for extremely long particles, with a transition to the SPP coupling interactions of a bilayer metallic film system beginning at a particle length of approximately 5 μm.
Abstract: We study the coupling interactions between a progressively elongated silver nanoparticle and a silver film on a glass substrate. Specifically, we investigate how the coupling between localized surface plasmons (LSPs) and propagating surface plasmon polaritons (SPPs) is influenced by nanoparticle length. Although the multiple resonances supported by the nanoparticle are effectively standing wave surface plasmons, their interaction with the SPP continuum of the underlying Ag film indicates that their spectral response is still localized in nature. It is found that these LSP-SPP interactions are not limited to small particles, but that they are present as well for extremely long particles, with a transition to the SPP coupling interactions of a bilayer metallic film system beginning at a particle length of approximately 5 μm.
TL;DR: A novel biosensing method based on the enhancement of the optical absorption spectrum of the hemoprotein cytochrome c when loaded into a highly scattering random medium enables, in contrast to existing techniques, non-invasive and dynamic detection of the oxidation of cyt c in the presence of H2O2 with unprecedented sensitivity.
Abstract: Reactive oxygen species play a key role in cell signalling and oxidative stress mechanisms, therefore, sensing their production by living organisms is of fundamental interest. Here we describe a novel biosensing method for extracellular detection of endogenous hydrogen peroxide (H2O2). The method is based on the enhancement of the optical absorption spectrum of the hemoprotein cytochrome c when loaded into a highly scattering random medium. Such a configuration enables, in contrast to existing techniques, non-invasive and dynamic detection of the oxidation of cyt c in the presence of H2O2 with unprecedented sensitivity. Dynamic information on the modification of the cell oxidative status of Chlamydomonas reinhardtii, an aquatic green algae, was obtained under oxidative stress conditions induced by the presence of trace concentrations of Cd(II). Furthermore, the dynamics of H2O2 production was investigated under different lighting conditions confirming the impact of Cd(II) on the photosynthetic activity of those phytoplanktonic cells.
TL;DR: In this paper, the authors presented a method to detect the presence of a virus in the human brain using the Web of Science Record (WRSR) created on 2013-06-11, modified on 2017-05-10.
Abstract: Reference EPFL-ARTICLE-186993doi:10.1002/adom.201200017View record in Web of Science Record created on 2013-06-11, modified on 2017-05-10
Proceedings Article•
01 Jan 2013TL;DR: In this paper, Nanophotonics and Plasmonics Reference EPFL-CONF-187056 Record created on 2013-06-17, modified on 2017-05-10
Abstract: Keywords: Nanophotonics ; Plasmonics Reference EPFL-CONF-187056 Record created on 2013-06-17, modified on 2017-05-10
23 Jun 2013
TL;DR: In this paper, full LQG adaptive optics (AO) control is validated for the first time on sky for classical AO and multi-object AO with 3 natural guide stars (GSs) and a Rayleigh laser GS, including vibration mitigation, on the Canary demonstrator (William Herschel Telescope, Spain).
Abstract: Full LQG adaptive optics (AO) control is validated for the first time on sky for classical AO and multi-object AO with 3 natural guide stars (GSs) and a Rayleigh laser GS, including vibration mitigation, on the Canary demonstrator (William Herschel Telescope, Spain).
TL;DR: Using Mie theory extended to second harmonic generation, the coupling between quadrupolar plasmon modes in metallic nanoshells was investigated in this article, where a universal scaling behavior was observed in agreement with the plasman hybridization model.
Abstract: The universal scaling of plasmon coupling in metallic nanostructures is now a well-established feature. However, if the interaction between dipolar plasmon modes has been intensively studied, this is not the case of the coupling between higher order ones. Using Mie theory extended to second harmonic generation, we investigate the coupling between quadrupolar plasmon modes in metallic nanoshells. Like in the case of dipolar plasmon modes, a universal scaling behavior is observed in agreement with the plasmon hybridization model.
DOI•
01 Dec 2013
TL;DR: The first on-sky results of full Multi-Object Adaptive Optics (MOAO) LQG control were obtained in Spring 2013 on the CANARY demonstrator at the William Herschel Telescope (La Palma, Spain) as discussed by the authors.
Abstract: We present in this paper the very first on-sky results of full Multi-Object Adaptive Optics (MOAO) LQG control (i.e. all modes, with coupling, controlled with an LQG regulator), obtained in Spring 2013 on the CANARY demonstrator at the William Herschel Telescope (La Palma, Spain). The MOAO on-sky pathfinder CANARY features two AO configurations that have both been tested: single-conjugated AO and multi-object AO with NGS and NGS+LGS, together with vibration mitigation on tip and tilt modes. The successful MOAO results are presented and shortly analyzed in terms of performance and tuning.
TL;DR: The second harmonic generation from gold nanoparticles trapped into realistic and idealized gold nanoantennas is numerically investigated using a surface integral equations technique and shows promise as a promising alternative to the conventional linear optical methods for the detection of trapping events at the nanoscale.
Abstract: The second harmonic generation from gold nanoparticles trapped into realistic and idealized gold nanoantennas is numerically investigated using a surface integral equations technique. It is observed that the presence of a nanoparticle in the nanoantenna gap dramatically modifies the second harmonic intensity scattered into the far-field. These results clearly demonstrate that second harmonic generation is a promising alternative to the conventional linear optical methods for the detection of trapping events at the nanoscale.
DOI•
01 Dec 2013
TL;DR: The Strehl ratio obtained with CuReD is at least as high as the one of MVM, and the performance of the traditional wavefront reconstruction (MVM) is compared by meuring theStrehl ratio.
Abstract: We have tested two novel wavefront reconstruction algorithms, CuReD an d HWR, using CANARY. We performed tests using telescope simulator and “on sky”, using William Herschel Telescope. Both CuReD and HWR ran successfully in closed loop. We compare d their performance with the performance of the traditional wavefront reconstruction (MVM) by me asuring the Strehl ratio. The Strehl ratio obtained with CuReD is at least as high as the one of MVM.
TL;DR: In this article, a portable analytical biosensor for real-time extracellular monitoring of released hydrogen peroxide (H2O2 ) is presented, which is based on the optical detection of the cytochrome c (cyt c) oxidation state.
Abstract: In this work a portable analytical biosensor for real-time extracellular monitoring of released hydrogen peroxide (H2O2 ) is presented. The biosensor is based on the optical detection of the cytochrome c (cyt c) oxidation state. The setup consists of an integrated microscope combined with a compact spectrometer. The light being absorbed by cyt c is enhanced via multiscattering produced by random aggregates of polystyrene beads in a cross-linked cyt c matrix. Using ink-jet printing technique, the sensing elements, namely cyt c loaded polystyrene aggregates, are fabricated with high reliability in terms of repeatability of size and sensitivity. Additionally, the sensing elements are enclosed in a microfluidic channel assuring a fast and efficient analytes delivery. As an example, the effect of trace concentrations of functionalized cadmium selenide/zinc sulfide (CdSe/ZnS) core shell quantum dots on the green algae Chlamydomonas reinhardtii is investigated, showing extracellular H2O2 release with different production rates over a period of 1 hour. In conclusion, the presented portable biosensor enables the highly sensitive and non-invasive real-time monitoring of the cell metabolism of C. reinhardtii. © (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
01 Mar 2013
TL;DR: In this paper, the authors explore the possibility of strongly influencing the plasmon damping time in nanostructures for efficient second harmonic generation, by taking advantage of the tunability of the narrow linewidth feature in the extinction cross-section exhibited by plasmoric nanostructure under Fano resonance.
Abstract: We explore the possibility of strongly influencing the plasmon damping time in nanostructures for efficient second harmonic generation, by taking advantage of the tunability of the narrow linewidth feature in the extinction cross-section exhibited by plasmonic nanostructures under Fano resonance.
01 Jan 2013
TL;DR: In this paper, the spectral resolution and contrast of sub-radiant modes are derived from the line shape in the far-field optical spectrum and an expression for the intrinsic width of a plasmonic mode is derived and calculated using perturbation.
Abstract: Plasmonic modes with long radiative lifetimes, subradiant modes, combine strong confinement of the electromagnetic energy at the nanoscalewithasteepspectraldispersion,whichmakesthempromisingfor biochemical sensors or immunoassays. Subradiant modes have three decay channels: Ohmic losses, their extrinsic coupling to radiation, and possibly their intrinsic dipole moment. In this work, the performance of subradiant modes for refractive index sensing is studied with a general analytical and numericalapproach.Weintroduceamodelfortheimpactthathasdifferent decay channels of subradiant modes on the spectral resolution and contrast. It is shown analytically and verified numerically that there exists an optimal value of the mode coupling for which the spectral dispersion of the resonance line shape is maximal. The intrinsic width of subradiant modes determines thevalueofthedispersionmaximumanddependsonthepenetrationoftheelectric fieldinthemetallicnanostructure.A figureofmerit,givenbytheratio ofthesensitivitytotheintrinsicwidth,whicharebothintrinsicpropertiesofsubradiantmodes,isintroduced.This figureofmeritcanbedirectlycalculated from the line shape in the far-field optical spectrum and accounts for the fact that both the spectral resolution and contrast determine the limit of detection. An expression for the intrinsic width of a plasmonic mode is derived and calculated from the line shape parameters and using perturbation
TL;DR: Sub-10 nm gap plasmonic gratings are experimentally studied for second harmonic generation (SHG) and a model is developed to explain the optimum in transmitted SHG, showing the interplay between the grating width and field enhancement.
Abstract: Sub-10 nm gap plasmonic gratings are experimentally studied for second harmonic generation (SHG) and a model is developed to explain the optimum in transmitted SHG, showing the interplay between the grating width and field enhancement.
TL;DR: In this paper, the role played by the nanostructure shape and the enhancement of second harmonic generation using Fano resonances was emphasized, and a simulation of realistic plasmonic nanoantennas and metamolecules was presented.
Abstract: In this presentation, second harmonic generation from realistic plasmonic nanoantennas and metamolecules will be discussed. The role played by the nanostructure shape and the enhancement of second harmonic generation using Fano resonances will be emphasized.