Achiral Magnetic Photonic Antenna as a Tunable Nanosource of Chiral Light
Cui, L., X. Yang, B. Reynier, C. Schwob, S. Bidault, B. Gallas, and M. Mivelle
ACS Photonics 10, no. 11, 3850-3857 (2023)
Résumé: Sensitivity to molecular chirality is crucial for many fields, from biology and chemistry to the pharmaceutical industry. By generating superchiral light, nanophotonics has brought innovative solutions to reduce the detection volume and increase sensitivity at the cost of a nonselectivity of light chirality or a strong contribution to the background. Here, we theoretically propose a simple achiral plasmonic resonator based on a rectangular nanoslit in a thin metallic layer behaving as a magnetic dipole to generate a tunable nanosource of purely chiral light working from the UV to the infrared. This nanosource is free of any background, and the sign of its chirality is externally tunable in wavelength and polarization. These unique properties, resulting from the coupling between the incident wave and the magnetic dipolar character of our nanoantenna, coupled with a method of Fluorescent Detected Circular Dichroism (FDCD), shown to be 2 orders of magnitude more sensitive than classical circular dichroism measurements, thus provide a platform with deep subwavelength detection volumes for chiral molecules and a roadmap for optimizing the signal-to-noise ratios in circular dichroism measurements to reach single-molecule sensitivity.
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A Magnetic Monopole Antenna
Reynier, B., X. Yang, B. Gallas, S. Bidault, and M. Mivelle
ACS Photonics 10, no. 9, 3070-3076 (2023)
Résumé: Magnetic monopoles are hypothetical particles which, similar to the electric monopoles that generate electric fields, are at the origin of magnetic fields. Despite many efforts, to date, these theoretical particles have yet to be observed. Nevertheless, many systems or physical phenomena mimic the behavior of magnetic monopoles. Here, we propose a new type of photonic nanoantenna behaving as a radiating magnetic monopole. We demonstrate that a half-nanoslit in a semi-infinite gold layer generates a single pole of enhanced magnetic field at the nanoscale and that this single pole radiates efficiently in the far field. We also introduce an effective magnetic charge using Gauss’s law of magnetism, in analogy to the electric charge, which further highlights the monopolar behavior of this new antenna. Finally, we show that different plasmonic and metallic materials can provide magnetic monopole antennas covering the visible-to-near infrared range, even down to GHz frequencies. This original antenna concept opens the way to a new model system to study magnetic monopoles and a new optical magnetic field source to study “magnetic light-matter coupling.” Furthermore, it shows potential applications at lower frequencies, such as in magnetic resonance imaging.
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Full control of electric and magnetic light-matter interactions through a nanomirror on a near-field tip
Reynier, B., E. Charron, O. Markovic, X. Yang, B. Gallas, A. Ferrier, S. Bidault, and M. Mivelle
Optica 10, no. 7, 841-845 (2023)
Résumé: Light-matter interactions are often considered governed by the electric optical field only, leaving aside the magnetic component of light. However, the magnetic part plays a determining role in many optical processes, from light and chiral-matter interactions and photon-avalanching to forbidden photochemistry, making the manipulation of magnetic processes extremely relevant. Here, by creating a standing wave using a metallic nanomirror, we manipulate the spatial distributions of electric and magnetic fields and their associated local densities of states, allowing selective control of the excitation and emission of electric and magnetic dipolar transitions. This control allows us to image, in 3D, the electric and magnetic nodes and anti-nodes of the fields' interference patterns. It also enables us to enhance specifically photoluminescence from quantum emitters excited only by the magnetic field, and to manipulate their spontaneous emission by acting on the excitation fields solely, demonstrating full control of magnetic and electric light-matter interactions.
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Dimers of Plasmonic Nanocubes to Reach Single-Molecule Strong Coupling with High Emission Yields
Heintz, J., F. Legittimo, and S. Bidault
The Journal of Physical Chemistry Letters 13, no. 51, 11996-12003 (2022)
Résumé: Reaching reproducible strong coupling between a quantum emitter and a plasmonic resonator at room temperature, while maintaining high emission yields, would make quantum information processing with light possible outside of cryogenic conditions. We theoretically propose to exploit the high local curvatures at the tips of plasmonic nanocubes to reach Purcell factors of >106 at visible frequencies, rendering single-molecule strong coupling more easily accessible than with the faceted spherical nanoparticles used in recent experimental demonstrations. In the case of gold nanocube dimers, we highlight a trade-off between coupling strength and emission yield that depends on the nanocube size. Electrodynamic simulations on silver nanostructures are performed using a realistic dielectric constant, as confirmed by scattering spectroscopy performed on single nanocubes. Dimers of silver nanocubes feature Purcell factors similar to those of gold while allowing emission yields of >60%, thus providing design rules for efficient strongly coupled hybrid nanostructures at room temperature.
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Transition from Phononic to Geometrical Mie Modes Measured in Single Subwavelength Polar Dielectric Spheres
Abou-Hamdan, L., L. Coudrat, S. Bidault, V. Krachmalnicoff, R. Haïdar, P. Bouchon, and Y. De Wilde
ACS Photonics 9, no. 7, 2295-2303 (2022)
Résumé: Spherical dielectric resonators are highly attractive for light manipulation, thanks to their intrinsic electric and magnetic resonances. Here, we present measurements of the mid-infrared far-field thermal radiation of single subwavelength dielectric spheres deposited on a gold substrate, of radii ranging from 1 to 2.5 μm, which agree quantitatively with simulated absorption cross sections. For SiO2microspheres, we evidence the excitation of both surface phonon-polariton (SPhP) modes and geometrical electric and magnetic Mie modes. The transition from a phonon-mode-dominated to a Mie-mode-dominated emission spectrum is observed, with a threshold radius of ∼1.5 μm. We also show that the presence of the metallic substrate augments the computed spheres absorption cross-section due to increased local field enhancement, arising from the near-field interaction of the spheres oscillating charges with their image in the metallic mirror. In contrast, measurements of single subwavelength SPhP-inactive PTFE spheres reveal that the mid-infrared response of such lossy spheres is dominated by their bulk absorption. Our results demonstrate how engineering the geometrical and dielectric properties of subwavelength scatterers can enable the control of thermal emission near room temperature, with exciting perspectives for applications such as radiative cooling.
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Few-Molecule Strong Coupling with Dimers of Plasmonic Nanoparticles Assembled on DNA
Heintz, J., N. Markešević, E. Y. Gayet, N. Bonod, and S. Bidault
ACS Nano 15, no. 9, 14732-14743 (2021)
Résumé: Hybrid nanostructures, in which a known number of quantum emitters are strongly coupled to a plasmonic resonator, should feature optical properties at room temperature such as few-photon nonlinearities or coherent superradiant emission. We demonstrate here that this coupling regime can only be reached with dimers of gold nanoparticles in stringent experimental conditions, when the interparticle spacing falls below 2 nm. Using a short transverse DNA double-strand, we introduce five dye molecules in the gap between two 40 nm gold particles and actively decrease its length down to sub-2 nm values by screening electrostatic repulsion between the particles at high ionic strengths. Single-nanostructure scattering spectroscopy then evidence the observation of a strong-coupling regime in excellent agreement with electrodynamic simulations. Furthermore, we highlight the influence of the planar facets of polycrystalline gold nanoparticles on the probability of observing strongly coupled hybrid nanostructures.
Mots-clés: strong coupling; plasmonics; DNA nanotechnology; self-assembly; scattering spectroscopy; dye molecules
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Statistical Nonlinear Optical Mapping of Localized and Delocalized Plasmonic Modes in Disordered Gold Metasurfaces
Roubaud, G., S. Bidault, S. Gigan, and S. Grésillon
ACS Photonics 8, no. 7, 1937-1943 (2021)
Résumé: Using a statistical analysis of nonlinear luminescence images measured with randomly wavefront-shaped femtosecond excitations, we provide direct insight on both the localized and delocalized plasmonic modes featured by disordered gold metasurfaces. We can independently image areas where far-field wavefront shaping can control the optical properties and areas with strong subwavelength optical hotspots. In practice, the fraction of the disordered plasmonic surface on which wavefront control is feasible depends strongly on the nanoscale morphology of the sample. Close to the percolation threshold, the entire surface is sensitive to wavefront shaping, and we observe the largest densities of delocalized modes as well as the strongest optical hotspots. These results demonstrate how statistical imaging schemes can offset the complexity of disordered nanophotonic systems in order to characterize their optical properties.
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Far-Field Wavefront Control of Nonlinear Luminescence in Disordered Gold Metasurfaces
Roubaud, G., P. Bondareff, G. Volpe, S. Gigan, S. Bidault, and S. Grésillon
Nano Letters 20, no. 5, 3291-3298 (2020)
Résumé: We demonstrate the local optimization of nonlinear luminescence from disordered gold metasurfaces by shaping the phase of femtosecond excitation. This process is enabled by the far-field wavefront control of plasmonic modes delocalized over the sample surface, leading to a coherent enhancement of subwavelength electric fields. In practice, the increase in nonlinear luminescence is strongly sensitive to both the nanometer-scale morphology and the level of structural complexity of the gold metasurface. We typically observe a 2 orders of magnitude enhancement of the luminescence signal for an optimized excitation wavefront compared to a random one. These results demonstrate how disordered metasurfaces made of randomly coupled plasmonic resonators, together with wavefront shaping, provide numerous degrees of freedom to program locally optimized nonlinear responses and optical hotspots.
Mots-clés: disordered media; metasurfaces; nonlinear luminescence; plasmonics; Wavefront shaping
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A dielectric magnetic nanoantenna designed by evolutionary optimization
Bonod, N., S. Bidault, G. W. Burr, and M. Mivelle
2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 (2019)
Résumé: © 2019 IEEE. Magnetic light and matter interactions are generally considered too weak to be detected, studied and applied technologically [1]. However, if one can increase the magnetic power density of light by several orders of magnitude, the coupling between magnetic light and matter could become of the same order of magnitude as the coupling with its electric counterpart. For that purpose, photonic nanoantennas have been proposed, and in particular dielectric nanostructures, to engineer strong local magnetic field and therefore increase the probability of magnetic interactions [2]. Unfortunately, dielectric designs suffer from physical limitations that confine the magnetic hot spot in the core of the material itself, preventing experimental and technological implementations. Here, we demonstrate that evolutionary algorithms [3] can overcome such limitations by designing new dielectric photonic nanoantennas, able to increase and extract the optical magnetic field from high refractive index materials. We also demonstrate that the magnetic power density in an evolutionary optimized dielectric nanostructure can be increased by a factor 5 compared to state-of-the-art dielectric nanoantennas [4]. In addition, we show that the fine details of the nanostructure are not critical in reaching these aforementioned features, as long as the general shape of the motif is maintained. This advocates for the feasibility of nanofabricating the optimized antennas experimentally and their subsequent application. By designing all-dielectric magnetic antennas that feature local magnetic hot-spots outside of high refractive index materials, this work highlights the potential of evolutionary methods to fill the gap between electric and magnetic light-matter interactions, opening up new possibilities in many research fields.
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Enhancing magnetic light emission with optical nanoantennas
Sanz-Paz, M., C. Ernandes, J. U. Esparza, G. W. Burr, N. F. Van Hulst, A. Maitre, L. Aigouy, N. Bonod, T. Gacoin, M. F. Garcia-Parajo, S. Bidault, and M. Mivelle
2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 (2019)
Résumé: © 2019 IEEE. Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields [1]. Here we experimentally demonstrate that properly designed photonic nanoantennas (figure 1a and b) can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals [2]. In particular, an enhancement of magnetic emission from trivalent europium-doped nanoparticles can only by observed in the vicinity of nanoantennas featuring a magnetic resonance [2,3]. Moreover, by controlling the spatial coupling between emitter and nanoresonator using a Near-field Scanning Optical Microscope (NSOM), local distributions of both magnetic and electric radiative local densities of states can be readily recorded with nanoscale precision (figure 1c and d), revealing the modification of the quantum environment induced by the presence of the nanoantennas. This manipulation and enhancement of magnetic light and matter interactions is a turning point in nanophotonics, opening up new possibilities for the research fields of opto-electronics, chiral optics, nonlinear nano-optics, spintronics and metamaterials, amongst others.
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Far-field wavefront optimization of the optical near-field in nanoscale disordered plasmonic metasurfaces
Roubaud, G., S. Bidault, S. Gigan, and S. Gresillon
2019 Conference on Lasers and Electro-Optics Europe and European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 (2019)
Résumé: © 2019 IEEE. Plasmonic nanoantennas featuring nanoscale gaps can exhibit strongly enhanced optical near-fields that have been extensively used in surface enhanced spectroscopy (Raman and Fluorescence) and in biosensing. However, deterministic nanostructures do not provide enough degrees of freedom to control optically these local field enhancements. By comparison, wavefront shaping techniques in disordered scattering media provide numerous degrees of freedom to control light focusing in space and time [1]. To associate local field enhancements and far-field wavefront control, we use disordered plasmonic surfaces close to the percolation threshold (see Fig. 1-a) that feature both hotspots [2] and delocalized plasmon modes. Disordered plasmonic surfaces can be controlled using a spatial light modulator [3].
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Dielectric nanoantennas to manipulate solid-state light emission
Bidault, S., M. Mivelle, and N. Bonod
Journal of Applied Physics 126, no. 9 (2019)
Résumé: © 2019 Author(s). Thanks to their enhanced and confined optical near-fields, broadband subwavelength resonators have the ability to enhance the spontaneous emission rate and brightness of solid-state emitters at room temperature. Over the last few years, high-index dielectrics have emerged as an alternative platform to plasmonic materials in order to design nanoresonators/optical nanoantennas with low ohmic losses. In particular, the excitation of electric and magnetic multipolar modes in dielectric resonators provides numerous degrees of freedom to manipulate the directivity and radiative decay rates of electric or magnetic quantum emitters. We review recent theoretical and experimental applications of dielectric nanoantennas to enhance or control decay rates of both electric and magnetic emitters but also to manipulate their radiation pattern through the coherent excitation of electric and magnetic modes; before discussing perspectives of this emerging field.
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Evolutionary Optimization of All-Dielectric Magnetic Nanoantennas
Bonod, N., S. Bidault, G. W. Burr, and M. Mivelle
Advanced Optical Materials 7, no. 10 (2019)
Résumé: © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Magnetic light and matter interactions are generally too weak to be detected, studied, and applied technologically. However, if one can increase the magnetic power density of light by several orders of magnitude, the coupling between magnetic light and matter could become of the same order of magnitude as the coupling with its electric counterpart. For that purpose, photonic nanoantennas, in particular dielectric, are proposed to engineer strong local magnetic field and therefore increase the probability of magnetic interactions. Unfortunately, dielectric designs suffer from physical limitations that confine the magnetic hot spot in the core of the material itself, preventing experimental and technological implementations. Here, it is demonstrated that evolutionary algorithms can overcome such limitations by designing new dielectric photonic nanoantennas, able to increase and extract the optical magnetic field from high refractive index materials. It is also demonstrated that the magnetic power density in an evolutionary optimized dielectric nanostructure can be increased by a factor 5 compared to state-of-the-art dielectric nanoantennas and that the fine details of the nanostructure are not critical in reaching these aforementioned features, as long as the general shape of the motif is maintained. This advocates for the feasibility of nanofabricating the optimized antennas experimentally and their subsequent application.
Mots-clés: dielectric nanoantennas; evolutionary algorithm; inverse design; light–matter interactions; magnetic light; nanophotonics
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Temperature-Dependent Plasmonic Responses from Gold Nanoparticle Dimers Linked by Double-Stranded DNA
Lermusiaux, L., and S. Bidault
Langmuir 34, no. 49, 14946-14953 (2018)
Résumé: © 2018 American Chemical Society. DNA is a powerful tool to assemble gold nanoparticles into discrete structures with tunable plasmonic properties for photonic or biomedical applications. Because of their photothermal properties or their use in biological media, these nanostructures can experience drastic modifications of the local temperature that can affect their morphology and, therefore, their optical responses. Using single-nanostructure spectroscopy, we demonstrate that, even with a fully stable DNA linker, gold particle dimers can undergo substantial conformational changes at temperatures larger than 50 °C and aggregate irreversibly. Such temperature-dependent resonant optical properties could find applications in imaging and in the design of nonlinear photothermal sources. Inversely, to provide fully stable DNA-templated plasmonic nanostructures at biologically relevant temperatures, we show how passivating the gold nanoparticles using amphiphilic surface chemistries renders the longitudinal plasmon resonance of gold particle dimers nearly independent of the local temperature.
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Enhancing Magnetic Light Emission with All-Dielectric Optical Nanoantennas
Sanz-Paz, M., C. Ernandes, J. U. Esparza, G. W. Burr, N. F. Van Hulst, A. Maitre, L. Aigouy, T. Gacoin, N. Bonod, M. F. Garcia-Parajo, S. Bidault, and M. Mivelle
Nano Letters 18, no. 6, 3481-3487 (2018)
Résumé: © 2018 American Chemical Society. Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields. Here, we experimentally demonstrate that properly designed photonic nanoantennas can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement of magnetic emission from trivalent europium-doped nanoparticles in the vicinity of a nanoantenna tailored to exhibit a magnetic resonance. Specifically, by controlling the spatial coupling between emitters and an individual nanoresonator located at the edge of a near-field optical scanning tip, we record with nanoscale precision local distributions of both magnetic and electric radiative local densities of states (LDOS). The map of the radiative LDOS reveals the modification of both the magnetic and electric quantum environments induced by the presence of the nanoantenna. This manipulation and enhancement of magnetic light-matter interaction by means of nanoantennas opens up new possibilities for the research fields of optoelectronics, chiral optics, nonlinear and nano-optics, spintronics, and metamaterials, among others.
Mots-clés: Dielectric and plasmonic nanoantennas; magnetic and electric LDOS; magnetic dipoles; magnetic light; near-field optical microscopy
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Enhancement and Inhibition of Spontaneous Photon Emission by Resonant Silicon Nanoantennas
Bouchet, D., M. Mivelle, J. Proust, B. Gallas, I. Ozerov, M. F. Garcia-Parajo, A. Gulinatti, I. Rech, Y. De Wilde, N. Bonod, V. Krachmalnicoff, and S. Bidault
Physical Review Applied 6, no. 6 (2016)
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All-Dielectric Silicon Nanogap Antennas To Enhance the Fluorescence of Single Molecules
Regmi, R., J. Berthelot, P. M. Winkler, M. Mivelle, J. Proust, F. Bedu, I. Ozerov, T. Begou, J. Lumeau, H. Rigneault, M. F. Garcia-Parajo, S. Bidault, J. Wenger, and N. Bonod
Nano Letters 16, no. 8, 5143-5151 (2016)
Mots-clés: All-dielectric nanophotonics; silicon resonators; optical antenna; fluorescence enhancement; Mie scattering
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Spatiotemporal Coherent Control of Light through a Multiple Scattering Medium with the Multispectral Transmission Matrix
Mounaix, M., D. Andreoli, H. Defienne, G. Volpe, O. Katz, S. Gresillon, and S. Gigan
Physical Review Letters 116, no. 25 (2016)
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Competition between Förster Resonance Energy Transfer and Donor Photodynamics in Plasmonic Dimer Nanoantennas
Bidault, S., A. Devilez, P. Ghenuche, B. Stout, N. Bonod, and J. Wenger
ACS Photonics 3, no. 5, 895-903 (2016)
Résumé: © 2016 American Chemical Society. Plasmonic optical antennas enhance and control the emission of quantum sources in the far-field. Interestingly, the antenna concept can also be applied to enhance the electric field produced by a quantum emitter in the near-field and increase the rate of Förster resonance energy transfer (FRET) between two nearby donor and acceptor dipole emitters. However, plasmonic antennas also influence numerous other photophysical processes such as the donor excitation intensity and decay dynamics and the acceptor emission yield, which compete with the observation of FRET. Understanding the balance between FRET and these processes and monitoring FRET under intense resonant optical confinement in plasmonic nanoantennas have remained challenging open questions. Here, we use DNA-driven self-assembly to accurately produce 40 and 60 nm gold nanoparticle dimer antennas containing a single FRET pair located in the center of a 14 nm gap. The spontaneous donor decay rate constants are increased by 2 orders of magnitude, creating high local densities of optical states (LDOS) to explore the link between LDOS and FRET. The antennas induce a 5-fold increase of Förster energy transfer rate constants associated with reduced transfer efficiencies, in good agreement with numerical simulations. The strong antenna-emitter interaction leads to the surprising association of an enhanced acceptor emission with a weak transfer efficiency. Our measurements exemplify the competition between radiative and nonradiative processes in complex nanophotonic systems and highlight geometrical parameters and design rules to optimize nanoantennas for nonradiative energy harvesting.
Mots-clés: DNA self-assembly; fluorescence enhancement; FRET; gold nanoparticle; LDOS; nanoantenna; plasmonics
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Picosecond Lifetimes with High Quantum Yields from Single-Photon-Emitting Colloidal Nanostructures at Room Temperature
Bidault, S., A. Devilez, V. Maillard, L. Lermusiaux, J.-M. Guigner, N. Bonod, and J. Wenger
Acs Nano 10, no. 4, 4806-4815 (2016)
Mots-clés: self-assembled nanostructures; plasmon-enhanced fluorescence; single-photon emission; fluorescence correlation spectroscopy; dark-field microscopy
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Fabrication of poly-crystalline Si-based Mie resonators via amorphous Si on SiO 2 dewetting
Naffouti, M., T. David, A. Benkouider, L. Favre, A. Ronda, I. Berbezier, S. Bidault, N. Bonod, and M. Abbarchi
Nanoscale 8, no. 5, 2844-2849 (2016)
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Probing Extended Modes on Disordered Plasmonic Networks by Wavefront Shaping
Bondareff, P., G. Volpe, S. Gigan, and S. Gresillon
ACS Photonics 2, no. 12, 1661-1662 (2015)
Résumé: © 2015 American Chemical Society. We experimentally study the optical field distribution on disordered plasmonic networks by far-field wavefront shaping. We observe nonlocal fluctuations of the field intensity mediated by plasmonic modes up to a distance of 10 μm from the excitation area. In particular we quantify the spatial extent of these fluctuations as a function of the metal filling fraction in the plasmonic network, and we identify a clear increase around percolation due to the existence of extended plasmonic modes. This paves the way toward far-field coherent control of plasmonic modes on similar disordered plasmonic networks. We expect these results to be relevant for quantum networks, coherent control, and light-matter interactions in such disordered films where long-range interactions are critical.
Mots-clés: disorder; far-field control; leaky wave microscopy; mode extension; plasmonic networks; surface plasmon; surface wave; wavefront shaping
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Increasing the Morphological Stability of DNA-Templated Nanostructures with Surface Hydrophobicity
Lermusiaux, L., and S. Bidault
Small 11, no. 42, 5696-5704 (2015)
Résumé: © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. DNA has been extensively used as a versatile template to assemble inorganic nanoparticles into complex architectures; thanks to its programmability, stability, and long persistence length. But the geometry of self-assembled nanostructures depends on a complex combination of attractive and repulsive forces that can override the shape of a molecular scaffold. In this report, an approach to increase the morphological stability of DNA-templated gold nanoparticle (AuNP) groupings against electrostatic interactions is demonstrated by introducing hydrophobicity on the particle surface. Using single nanostructure spectroscopy, the nanometer-scale distortions of 40 nm diameter AuNP dimers are compared with different hydrophilic, amphiphilic, neutral, and negatively charged surface chemistries, when modifying the local ionic strength. It is observed that, with most ligands, a majority of studied nanostructures deform freely from a stretched geometry to touching particles when increasing the salt concentration while hydrophobicity strongly limits the dimer distortions. Furthermore, an amphiphilic surface chemistry provides DNA-linked AuNP dimers with a high long-term stability against internal aggregation.
Mots-clés: amphiphilic ligands; darkfield microscopy; DNA nanotechnology; nanostructures; self-assembly
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Deterministic control of broadband light through a multiply scattering medium via the multispectral transmission matrix.
Andreoli, D., G. Volpe, S. Popoff, O. Katz, S. Gresillon, and S. Gigan
Scientific reports 5, 10347 (2015)
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Widefield spectral monitoring of nanometer distance changes in DNA-templated plasmon rulers
Lermusiaux, L., V. Maillard, and S. Bidault
ACS Nano 9, no. 1, 978-990 (2015)
Résumé: © 2015 American Chemical Society. The nanometer-scale sensitivity of electromagnetic plasmon coupling allows the translation of minute morphological changes in nanostructures into macroscopic optical signals. We demonstrate here a widefield spectral analysis of 40 nm diameter gold nanoparticle (AuNP) dimers, linked by a short DNA double strand, using a low-cost color CCD camera and allowing a quantitative estimation of interparticle distances in a 3-20 nm range. This analysis can be extended to lower spacings and a parallel monitoring of dimer orientations by performing a simple polarization analysis. Our measurement approach is calibrated against confocal scattering spectroscopy using AuNP dimers that are distorted from a stretched geometry at low ionic strength to touching particles at high salt concentrations. We then apply it to identify dimers featuring two different conformations of the same DNA template and discuss the parallel colorimetric sensing of short sequence-specific DNA single strands using dynamic plasmon rulers.
Mots-clés: colorimetric sensing; darkfield microscopy; DNA self-assembly; dynamic nanostructures; plasmon ruler; widefield spectroscopy
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Wafer Scale Formation of Monocrystalline Silicon-Based Mie Resonators via Silicon-on-Insulator Dewetting
Abbarchi, M., M. Naffouti, B. Vial, A. Benkouider, L. Lermusiaux, L. Favre, A. Ronda, S. Bidault, I. Berbezier, and N. Bonod
Acs Nano 8, no. 11, 11181-11190 (2014)
Mots-clés: Mie resonators; thin fim dewetting; all-dielectric nanophotonics; silicon nanoparticles
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Self-Assembled Plasmonic Oligomers for Organic Photovoltaics
Pastorelli, F., S. Bidault, J. Martorell, and N. Bonod
Advanced Optical Materials 2, no. 2, 171-175 (2014)
Mots-clés: organic photovoltaics; plasmonic oligomers; plasmonic solar cells; gold particles
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Selective Excitation of Single Molecules Coupled to the Bright Mode of a Plasmonic Cavity
Busson, M. P., and S. Bidault
Nano Letters 14, no. 1, 284-288 (2014)
Mots-clés: Plasmon coupling; DNA self-assembly; single molecule; Purcell effect; cylindrical vector beam; radial polarization
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Reversible switching of the interparticle distance in DNA-templated gold nanoparticle dimers
Lermusiaux, L., A. Sereda, B. Portier, E. Larquet, and S. Bidault
ACS Nano 6, no. 12, 10992-10998 (2012)
Résumé: We produce gold nanoparticle dimers with a surface-to-surface distance that varies reversibly by a factor of 3 when hybridizing or removing a single target DNA strand. The dimers are built on one DNA template that features a stem-loop enabling the interparticle distance change. Using electrophoresis, we reach 90% sample purities and demonstrate that this chemical process is reversible in solution at room temperature for a low molar excess of the target DNA strand. The kinetics of the reaction is asymmetric due to steric hindrance in the stem-loop opening process. Furthermore, a statistical analysis of cryo-electron microscopy measurements allows us to provide the first quantitative analysis of distance changes in chemically switchable nanoparticle assemblies. © 2012 American Chemical Society.
Mots-clés: cryo-electron microscopy; DNA self-assembly; dynamic nanostructures; electrophoresis; gold nanoparticles; Chemical process; Cryo-electron microscopy; DNA self-assembly; DNA strands; DNA-template; Gold Nanoparticles; Interparticle distances; Molar excess; Nanoparticle assemblies; Opening process; Reversible switching; Room temperature; Stem-loop; Steric hindrances; Surface-to-surface distances; Switchable; Electron microscopes; Electrophoresis; Gold; Metal nanoparticles; Reaction kinetics; DNA; D
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Near-field phase analysis reveals unexpected scattering properties of optical antennas
Rolly, B., B. Stout, S. Bidault, and N. Bonod
2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012)
Résumé: We demonstrate that a thorough study of the phase between nearby dipoles offers new insights in the design of nanoantennas and in the integration of dipolar emitters into metallic nanostructures. © 2012 OSA.
Mots-clés: Metallic nanostructure; Nanoantennas; Near-field; Optical antennas; Phase analysis; Scattering property; Lasers
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Photonic engineering of hybrid metal-organic chromophores
Busson, M. P., B. Rolly, B. Stout, N. Bonod, J. Wenger, and S. Bidault
Angewandte Chemie - International Edition 51, no. 44, 11083-11087 (2012)
Résumé: An aureate dye: Confined electromagnetic fields in DNA-templated gold nanoparticle dimers were tuned to engineer the fluorescence properties of organic dyes in water (see picture). Purified suspensions of hybrid metal-organic chromophores featured unprecedented photophysical properties, such as a short lifetime and low quantum yield but high brightness. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Mots-clés: DNA; fluorescence; fluorescence correlation spectroscopy; nanoparticles; self-assembly; Fluorescence Correlation Spectroscopy; Fluorescence properties; Gold Nanoparticles; High brightness; Metal-organic; Organic dye; Photonic engineering; Photophysical properties; DNA; Electromagnetic fields; Fluorescence; Fluorescence spectroscopy; Nanoparticles; Quantum yield; Self assembly; Chromophores; DNA; fluorescent dye; gold; organogold compound; article; chemistry; diffusion; dimerization; optics; solu
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Accelerated single photon emission from dye molecule-driven nanoantennas assembled on DNA
Busson, M. P., B. Rolly, B. Stout, N. Bonod, and S. Bidault
Nature Communications 3 (2012)
Résumé: A photon interacts efficiently with an atom when its frequency corresponds exactly to the energy between two eigenstates. But at the nanoscale, homogeneous and inhomogeneous broadenings strongly hinder the ability of solid-state systems to absorb, scatter or emit light. By compensating the impedance mismatch between visible wavelengths and nanometre-sized objects, optical antennas can enhance light-matter interactions over a broad frequency range. Here we use a DNA template to introduce a single dye molecule in gold particle dimers that act as antennas for light with spontaneous emission rates enhanced by up to two orders of magnitude and single photon emission statistics. Quantitative agreement between measured rate enhancements and theoretical calculations indicate a nanometre control over the emitter-particle position while 10 billion copies of the target geometry are synthesized in parallel. Optical antennas can thus tune efficiently the photo-physical properties of nano-objects by precisely engineering their electromagnetic environment. © 2012 Macmillan Publishers Limited. All rights reserved.
Mots-clés: atto647n dye; dimer; DNA; fluorescent dye; gold nanoparticle; unclassified drug; coloring agent; nanomaterial; antenna; article; calculation; DNA template; electromagnetic field; energy conversion; energy transfer; fluorescence; geometry; light; light harvesting system; nanoantenna; particle size; photochemistry; photon; bioengineering; chemistry; methodology; nanotechnology; Bioengineering; Coloring Agents; DNA; Nanostructures; Nanotechnology; Photons
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Promoting magnetic dipolar transition in trivalent lanthanide ions with lossless Mie resonances
Rolly, B., B. Bebey, S. Bidault, B. Stout, and N. Bonod
Physical Review B - Condensed Matter and Materials Physics 85, no. 24 (2012)
Résumé: Mie resonances in dielectric particles can increase the local optical density of states (LDOS) associated with either electric or magnetic transition rates in nearby quantum emitters without ohmic losses. Their rather large quality factors compensate their low field confinement as compared to the plasmon resonances of metallic nanostructures for which nonradiative decay channels dominate. We show theoretically that near-infrared quadrupolar magnetic resonances in silicon particles can preferentially promote magnetic versus electric radiative deexcitation in trivalent erbium ions at 1.54 μm. The distance dependent interaction between magnetic (electric) dipole emitters and induced magnetic or electric dipoles and quadrupoles is derived analytically and compared to quasiexact full-field calculations based on Mie theory. We discuss how near-field coupling between nearby particles can further enhance the magnetic LDOS and compensate for the weak refractive index contrasts between dielectric particles and a typical host matrix for the lanthanide ions. © 2012 American Physical Society.
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Digital heterodyne holography reveals the non-quasi-static scattering behaviour of transversally coupled nanodisk pairs
Suck, S. Y., S. Bidault, N. Bonod, S. Collin, N. Bardou, Y. De Wilde, and G. Tessier
International Journal of Optics 2012 (2012)
Résumé: We reconstruct the full three-dimensional scattering pattern of longitudinal and transverse modes in pairs of coupled gold nanodisks using digital heterodyne holography. Near-field simulations prove that, in our experimental conditions, the induced dipoles in the longitudinal mode are in phase while they are nearly in opposite phase for the transverse mode. The scattering efficiency of the two modes is of the same order of magnitude, which goes against the common belief that antisymmetric transverse modes are dark. The analysis of the reconstructed hologram in the Fourier plane allows us to estimate the angular scattering pattern for both excited modes. In particular, the antisymmetric transverse mode scatters light mostly into one half-plane, demonstrating that the quasi-static approximation breaks down in nanodisk pairs even for an interparticle distance lower than 4. Copyright © 2012 Sarah Y. Suck et al.
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Water-based assembly and purification of plasmon-coupled gold nanoparticle dimers and trimers
Bidault, S., and A. Polman
International Journal of Optics 2012 (2012)
Résumé: We describe a simple one-pot water-based scheme to produce gold nanoparticle groupings with short interparticle spacings. This approach combines a cross-linking molecule and a hydrophilic passivation layer to control the level of induced aggregation. Suspensions of dimers and trimers are readily obtained using a single electrophoretic purification step. The final interparticle spacings allow efficient coupling of the particle plasmon modes as verified in extinction spectroscopy. Copyright © 2012 Sébastien Bidault and Albert Polman.
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Optical and topological characterization of gold nanoparticle dimers linked by a single DNA double strand
Busson, M. P., B. Rolly, B. Stout, N. Bonod, E. Larquet, A. Polman, and S. Bidault
Nano Letters 11, no. 11, 5060-5065 (2011)
Résumé: We demonstrate that symmetric or asymmetric gold nanoparticle dimers with substantial scattering cross sections and plasmon coupling can be produced with a perfectly controlled chemical environment and a high purity using a single DNA linker as short as 7 nm. A statistical analysis of the optical properties and morphology of single dimers is performed using darkfield and cryo-electron microscopies. These results, correlated to Mie theory calculations, indicate that the particle dimers are stretched in water by electrostatic interactions. © 2011 American Chemical Society.
Mots-clés: Chemical environment; Cryo-electron microscopy; Dark-field; DNA Double strands; DNA linkers; Gold Nanoparticles; High purity; Mie theory; Plasmon coupling; Scattering cross section; Nanoparticles; Optical properties; Dimers
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On the phase of the electric field in optical antennas
Rolly, B., B. Stout, S. Bidault, and N. Bonod
AIP Conference Proceedings 1398, 88-90 (2011)
Résumé: We study the phase of the electric field in the vicinity of two electric dipoles transversely coupled in two fundamental cases: a nanogap antenna illuminated from the far field and a directive antenna made of a single metallic particle coupled to an electric source dipole. We will link the scattering efficiency of the dimer (first case) and the directivity of the particle antenna (second case) to the relative phase of the two dipoles. The strong distance dependence of this phase term produces two unexpected effects: the bonding transverse mode can be the brightest mode of a nanogap antenna; and the emission directivity offered by a metallic particle can be tuned by varying the emitter/particle distance at a strongly sub-wavelength scale. © 2011 American Institute of Physics.
Mots-clés: electric dipole radiation; light scattering; nano-optics; Nanoantennas; near field; plasmonics
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Crucial role of the emitter-particle distance on the directivity of optical antennas
Rolly, B., B. Stout, S. Bidault, and N. Bonod
Optics Letters 36, no. 17, 3368-3370 (2011)
Résumé: We demonstrate that the reflecting properties of a single particle nanoantenna can be extremely sensitive to its distance from a quantum emitter at frequencies lower than the plasmon resonance. The phenomenon is shown to arise from rapid phase variations of the emitter field at short distances associated with a phase of the antenna particle polarizability lower than π/4. © 2011 Optical Society of America.
Mots-clés: Directivity; Nanoantennas; Optical antennas; Phase variation; Plasmon resonances; Polarizabilities; Short distances; Single particle; Antennas
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Direct determination of diffusion properties of random media from speckle contrast
Curry, N., P. Bondareff, M. Leclercq, N. F. Van Hulst, R. Sapienza, S. Gigan, and S. Grésillon
Optics Letters 36, no. 17, 3332-3334 (2011)
Résumé: We present a simple scheme to determine the diffusion properties of a thin slab of strongly scattering material by measuring the speckle contrast resulting from the transmission of a femtosecond pulse with controlled bandwidth. In contrast with previous methods, our scheme does not require time measurements nor interferometry. It is well adapted to the characterization of samples for pulse shaping, nonlinear excitation through scattering media, and biological imaging. © 2011 Optical Society of America.
Mots-clés: Biological imaging; Diffusion properties; Direct determination; Femtosecond pulse; Nonlinear excitation; Pulse-shaping; Random media; Scattering materials; Scattering media; Thin slab; Electromagnetic pulse; Scattering; Slab mills; Speckle; Contrast media
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Low temperature near-field scanning optical microscopy of IR and THz surface-plasmon quantum cascade lasers
Moldovan-Doyen, I., A. Babuty, A. Bousseksou, R. Colombelli, S. Grésillon, and Y. De Wilde
Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)
Résumé: We present the first scattering type near-field scanning optical microscope operating at low temperature. This instrument is ideal to study infrared and terahertz QCLs combined with metallic photonic crystal resonators and surface plasmon waveguides. © 2010 Optical Society of America.
Mots-clés: Low temperatures; Metallic photonic crystals; Near-field scanning optical microscope; Surface plasmon waveguide; Surface-plasmon; Tera Hertz; Photonic crystals; Plasmons; Quantum cascade lasers; Near field scanning optical microscopy
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Ultracompact and unidirectional metallic antennas
Bonod, N., A. Devilez, B. Rolly, S. Bidault, and B. Stout
Physical Review B - Condensed Matter and Materials Physics 82, no. 11 (2010)
Résumé: We investigate the angular redistribution of light radiated by a single emitter located in the vicinity of dipolar silver nanoparticles. We point out the fundamental role of the phase differences introduced by the optical path difference between the emitter and the particle and demonstrate that the polarizability of the metallic nanoparticle alone cannot predict the emission directionality. In particular, we show that collective or reflective properties of single nanoparticles can be controlled by tuning the distance of a single emitter at a λ/30 scale. These results enable us to design unidirectional and ultracompact nanoantennas composed of just two coupled nanoparticles separated by a distance achievable with biological linkers. © 2010 The American Physical Society.
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Nanoparticle for active plasmonic device
Delahaye, J., S. Gresillon, and E. Fort
Proceedings of SPIE - The International Society for Optical Engineering 7608 (2010)
Résumé: Active plasmonic devices are much promising for optical devices and circuits at the nanoscale. We show that single nanoparticles coupled to metallic surfaces are good candidates for integrated components with nanometric dimensions. The localized plasmon of the nanoparticle launches propagating surface plasmons in the metallic thin film. Direct particle observation using leaky wave microscope geometry permits easy detection through the interference of the direct transmitted excitation light and the surface plasmon leaky mode. Investigations of the optical response of a nanoparticle deposited on metallic thin metal films reveals unexpectedly high transmission of light associated to contrast inversion in the images. © 2010 Copyright SPIE - The International Society for Optical Engineering.
Mots-clés: Leaky wave; Metal particle; Microscopy; Plasmon; Polariton; Excitation light; High transmission; Leaky modes; Leaky waves; Metal particle; Metallic surface; Metallic thin films; Nano scale; Nanometric dimensions; Optical response; Plasmon-polaritons; Plasmonic devices; Single nanoparticle; Surface plasmons; Thin metal films; Light transmission; Metallic compounds; Nanoparticles; Nanophotonics; Nanotechnology; Optical data storage; Optical instruments; Phonons; Photons; Quantum theory; Plasmons
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Fluorescence correlation spectroscopy on nano-fakir surfaces
Delahaye, J., S. Gresillon, S. Lévêque-Fort, N. Sojic, and E. Fort
Progress in Biomedical Optics and Imaging - Proceedings of SPIE 7571 (2010)
Résumé: Single biomolecule behaviour can reveal crucial information about processes not accessible by ensemble measurements. It thus represents a real biotechnological challenge. Common optical microscopy approaches require pico- to nano-molar concentrations in order to isolate an individual molecule in the observation volume. However, biologically relevant conditions often involve micromolar concentrations, which impose a drastic reduction of the conventional observation volume by at least three orders of magnitude. This confinement is also crucial for mapping sub-wavelength heterogeneities in cells, which play an important role in many biological processes. We propose an original approach, which couples Fluorescence Correlation Spectroscopy (FCS), a powerful tool to retrieve essential information on single molecular behaviour, and nano-fakir substrates with strong field enhancements and confinements at their surface. These electromagnetic singularities at nanometer scale, called "hotspots", are the result of the unique optical properties of surface plasmons. They provide an elegant means for studying single-molecule dynamics at high concentrations by reducing dramatically the excitation volume and enhancing the fluorophore signal by several orders of magnitude. The nano-fakir substrates used are obtained from etching optical fiber bundles followed by sputtering of a gold thin-film. It allows one to design reproducible arrays of nanotips. © 2010 Copyright SPIE - The International Society for Optical Engineering.
Mots-clés: Electromagnetic enhancement; Fluorescence correlation spectroscopy; Surface plasmon; Biological process; Electromagnetic enhancement; Fluorescence Correlation Spectroscopy; High concentration; Hotspots; In-cell; Micromolar concentration; Molar concentration; Nano-meter scale; Optical fiber bundle; Orders of magnitude; Single-molecule dynamics; Strong field enhancement; Sub-wavelength; Surface plasmons; Three orders of magnitude; Electromagnetism; Fluorescence; Fluorescence spectroscopy; Molecule
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Nanoparticle based integrated plasmonic component
Delahaye, J., S. Grésillon, and E. Fort
CLEO/Europe - EQEC 2009 - European Conference on Lasers and Electro-Optics and the European Quantum Electronics Conference (2009)
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Narrowing of non linear enhancements in near-field images
Grésillon, S., L. Williame, E. L. Moal, E. Fort, and A. C. Boccara
Proceedings of SPIE - The International Society for Optical Engineering 6324 (2006)
Résumé: In our attempt to reveal highly localized field enhancements on random metallic films using near-field scattering probe microscopy we experimentally demonstrated the existence of narrow peaks when using a monochromatic illumination. In order to get a better understanding of the second harmonic generation taking place on such films we have undertaken the same kind of near-field experiments using femtosecond lasers sources with high peak power able to induce the non linear response. These lasers have a spectral bandwidth associated with the pulse duration, which is in the femtosecond range. With such spectral broadening we have observed, as expected, a spatial broadening of the peaks at ω, which spread over distances in the 100-500 nm range. The behavior of the peaks is quite different at 2 ω: they are found to be always very well localized (∼10 nm) despite of the polychromatic nature of the light; moreover there is no clear correlation between the peaks position at ω and those at 2 ω. This observation indicates, as often underlined in non linear processes, that coherent interactions involving a distribution of available frequencies in the lasers spectra take place. These frequencies ωn, coherently induce second harmonic generation as long as ωn + ωm = 2 ω.
Mots-clés: Electromagnetic enhancement; Local second harmonic generation; Metal dielectric films; Near-field optics; Laser pulses; Metallic films; Monochromators; Near field scanning optical microscopy; Second harmonic generation; Electromagnetic enhancement; Local second harmonic generation; Metal dielectric films; Near field optics; Image enhancement
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Imaging subwavelength holes in chromium films in scanning near-field optical microscopy. Comparison between experiments and calculation
Ducourtieux, S., S. Grésillon, J. C. Rivoal, C. Vannier, C. Bainier, D. Courjon, and H. Cory
EPJ Applied Physics 26, no. 1, 35-43 (2004)
Résumé: Near-field optical signals are imaged in the vicinity of nano-holes using two different near-field optical microscopes. The experimental results are compared with electromagnetic field calculations based on a modal approximation. It turns out that an optical fibre detects the Poynting vector whereas the apertureless tip is sensitive to the field amplitude. © EDP Sciences.
Mots-clés: Approximation theory; Electromagnetic field effects; Optical fibers; Optical microscopy; Surfaces; Thin films; Vectors; Apertureless tip; Field amplitude; Imaging subwavelength holes; Poynting vector; Scanning near field optical microscopy; Chromium
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Near-field optical studies of semicontinuous metal films
Ducourtieux, S., V. A. Podolskiy, S. Grésillon, S. Buil, B. Berini, P. Gadenne, A. C. Boccara, J. C. Rivoal, W. D. Bragg, K. Banerjee, V. P. Safonov, V. P. Drachev, Z. C. Ying, A. K. Sarychev, and V. M. Shalaev
Physical Review B - Condensed Matter and Materials Physics 64, no. 16, 1654031-16540314 (2001)
Résumé: Local field distributions in random metal-dielectric films near a percolation threshold are experimentally studied using scanning near-field optical microscopy (SNOM). The surface-plasmon oscillations in such percolation films are localized in small nanometer-scale areas, "hot spots", where the local fields are much larger than the field of an incident electromagnetic wave. The spatial positions of the hot spots vary with the wavelength and polarization of the incident beam. Local near-field spectroscopy of the hot spots is performed using our SNOM. It is shown that the resonance quality-factor of hot spots increases from the visible to the infrared. Giant local optical activity associated with chiral plasmon modes has been obtained. The hot spot's large local fields may result in local, frequency and spatially selective photomodification of percolation films.
Mots-clés: metal; article; dielectric constant; electromagnetic field; film; microscopy; molecular interaction; oscillation; polarization; spectroscopy; surface plasmon resonance
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Experimental observation of percolation-enhanced nonlinear light scattering from semicontinuous metal films
Breit, M., V. A. Podolskiy, S. Grésillon, G. Von Plessen, J. Feldmann, J. C. Rivoal, P. Gadenne, A. K. Sarychev, and V. M. Shalaev
Physical Review B - Condensed Matter and Materials Physics 64, no. 12, 1251061-1251065 (2001)
Résumé: Strongly enhanced second-harmonic generation (SHG), which is characterized by a nearly isotropic intensity distribution, is observed for gold-glass films near the percolation threshold. The diffuselike SHG scattering, which can be thought of as nonlinear critical opalescence, is in sharp contrast with highly collimated linear reflection and transmission from these nanostructured semicontinuous metal films. Our observations, which can be explained by giant fluctuations of local nonlinear sources for SHG due to plasmon localization, verify recent predictions of percolation-enhanced nonlinear scattering.
Mots-clés: glass; gold; article; chemical structure; film; light scattering; nanoparticle; polarimetry; prediction; reflectometry
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Nanometer scale apertureless near field microscopy
Grésillon, S., S. Ducourtieux, A. Lahrech, L. Aigouy, J. C. Rivoal, and A. C. Boccara
Applied Surface Science 164, no. 1-4, 118-123 (2000)
Résumé: It is necessary to use the information contained in the near field to get sub-wavelength details in optical imaging which are not revealed through the far-field image. We have designed and built various setups able to perform near-field measurements in the UV, visible and IR, both in transmission, reflection and dark field with a resolution of 10 nm, independent of the wavelength but related to the tip size. Images revealing local dielectric contrasts, small particle effects, as well as local field enhancements in random structures, are shown. © 2000 Published by Elsevier Science B.V.
Mots-clés: Field enhancement; Local properties; Near field
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Percolation and fractal composites: Optical studies
Ducourtieux, S., S. Grésillon, A. C. Boccara, J. C. Rivoal, X. Quelin, P. Gadenne, V. P. Drachev, W. D. Bragg, V. P. Safonov, V. A. Podolskiy, Z. C. Ying, R. L. Armstrong, and V. M. Shalaev
Journal of Nonlinear Optical Physics and Materials 9, no. 1, 105-116 (2000)
Résumé: Local field distributions arc studied in random metal-dielectric films near percolation (percolation films) and fractal aggregates of colloidal particles. For both systems, it is shown that optical excitations are localized in small nanometer-scale areas, "hot spots," where the local fields are much larger than the field of an incident electromagnetic wave. The large local fields result in giant enhancement of various optical phenomena. The surface-enhanced white-light generation and second-harmonic generation have been obtained in percolation films. For fractal aggregates of silver particles, a giant effect of local optical activity has been observed. The effect is due to surface-plasmon excitations localized on chiral-active particle configurations in fractals.
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Direct observation of locally enhanced electromagnetic field
Gadenne, P., X. Quelin, S. Ducourtieux, Samuel Gresillon, L. Aigouy, J.-C. Rivoal, V. Shalaev, and A. Sarychev
Physica B: Condensed Matter 279, no. 1-3, 52-55 (2000)
Résumé: Surface enhanced Raman scattering and other nonlinear enhanced optical effects are well known to be induced by the surface of discontinuous or rough metal thin films. In the percolating range of concentration, theoretical calculations lead to locally enhanced field distributions at the surface of the films, due to huge fluctuations close to the phase transition threshold. Using a scanning near-field optical microscope (SNOM) of extremely high lateral resolution (10 nm), we have been able to record the field distribution close to the surface of discontinuous gold films in both transmission and reflection modes. We report here the direct observations, at a scale much shorter than the wavelength, of the giant field peaks, the so-called `hot spots'. Their intensities and spatial distribution are found in good agreement with the theoretical predictions.
Mots-clés: Electromagnetic fields; Gold; Light reflection; Light transmission; Optical microscopy; Percolation (solid state); Raman scattering; Thin films; Anderson localization; Scanning near-field optical microscopes (SNOM); Surface enhanced Raman scattering (SERS); Surface plasmon modes; Metallic films
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Nanoscale observation of enhanced electromagnetic field
Grésillon, S., J.-C. Rivoal, P. Gadenne, X. Quélin, V. Shalaev, and A. Sarychev
Physica Status Solidi (A) Applied Research 175, no. 1, 337-343 (1999)
Résumé: The surface of nanosized discontinuous or rough metal thin films is able to induce Raman scattering enhanced by several orders of magnitude. This effect has been theoretically attributed to the local field distribution at the surface of the films. As for the relevant parameter in phase transitions, the fields experience here huge fluctuations, leading to localized giant peaks so called `hot spots'. Using a Scanning Near-Field Optical Microscope (SNOM) of extremely high lateral resolution (10 nm), we have been able to record the field distribution close to the surface of gold films. We report here the first direct observation of the hot spots with such lateral resolution. Their intensities and spatial distribution are found in good agreement with the theoretical predictions. We also have performed local spectroscopy, which shows up sharp variations at nanometric scale (much smaller than the wavelength).
Mots-clés: Electromagnetic field effects; Gold; Image analysis; Image quality; Nanostructured materials; Optical microscopy; Phase transitions; Raman scattering; Surface roughness; Thin films; Nanoscale observations; Scanning near-field optical microscopy (SNOM); Metallic films
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Experimental observation of localized optical excitations in random metal-dielectric films
Grésillon, S., L. Aigouy, A. C. Boccara, J. C. Rivoal, X. Quelin, C. Desmarest, P. Gadenne, V. A. Shubin, A. K. Sarychev, and V. M. Shalaev
Physical Review Letters 82, no. 22, 4520-4523 (1999)
Résumé: The localized optical excitations in random metal-dielectric films were examined by scanning near-field optical microscopy. The patterns of the observed surface plasmon modes localized in hot spots are attributed to Anderson electron localization and are found to agree with theoretical predictions.
Mots-clés: Dielectric films; Electric fields; Electron resonance; Electron transitions; Mathematical models; Metallic films; Optical microscopy; Scanning; Semiconducting films; Anderson electron localization; Optical excitation; Plasmons; Scanning near-field optical microscopy (SNOM); Optical films
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Electric field diffraction by a semi-infinite perfectly conducting plane of small thickness: application to near-field microscopy
Cory, H., A. C. Boccara, J. C. Rivoal, and S. Grésillon
Microwave and Optical Technology Letters 21, no. 3, 177-183 (1999)
Résumé: A perfectly conducting half plane of finite thickness much smaller than the wavelength of the incident electromagnetic wave is investigated. The geometry of the structure is defined according to a transformation which is a particular case of the Schwarz-Christoffel transformation, representing a step with a slightly concave edge instead of the usual straight one. The solutions of the partial differential equations describing the structure are given for specific ranges of the variables, and the results obtained with this method are compared to those obtained with an independent numerical method for a step with a straight edge. Good agreement is obtained between the two sets of results, except right around the edges of the steps in the two structures, due to the different shapes involved. It is shown that the width of the structure has but a slight influence on the value of the electric field, while the angle of incidence of the incoming wave has a strong influence on this value.
Mots-clés: Diffraction; Electromagnetic fields; Electromagnetic wave propagation; Light polarization; Mathematical transformations; Numerical methods; Optical microscopy; Partial differential equations; Thickness measurement; Angle of incidence; Electric field diffraction; Electric field intensity; Near field microscopy; Electric fields
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Transmission-mode apertureless near-field microscope: optical and magneto-optical studies
Grésillon, S., H. Cory, J. C. Rivoal, and A. C. Boccara
Journal of Optics A: Pure and Applied Optics 1, no. 2, 178-184 (1999)
Résumé: A new near-field optical microscope working in transmission is presented. Lateral optical resolution less than 10 nm is obtained with a pure metallic probe. Polarization images of a metallic step confirmed the good resolution by comparison with an analytical model. We also demonstrate the capability of the microscope to obtain images with polarization effects. The good resolution is used for the observation of small gold aggregates which confirm that this microscope is able to make spectroscopic measurements of the optical effect induced by a nanometric scale particle. The polarization sensibility allows us to measure near-field magneto-optical contrast on a multi-layer sample with magnetic domains. These results are promising for magneto-optical characterization with nanometre resolution.
Mots-clés: Computer simulation; Gold; Light polarization; Light transmission; Magnetic domains; Magnetooptical effects; Mathematical models; Optical resolving power; Spectroscopy; Near field optics; Near field simulation; Optical microscope; Polarization effects; Optical microscopy
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