Showing papers by "Olivier J. F. Martin published in 2019"

Electronic Structure-Dependent Surface Plasmon Resonance in Single Au-Fe Nanoalloys.

Abstract: The relationship between composition and plasmonic properties in noble metal nanoalloys is still largely unexplored. Yet, nanoalloys of noble metals, such as gold, with transition elements, such as...

Modes interplay and dynamics in the second harmonic generation of plasmonic nanostructures

Abstract: The full wave surface integral equation computation of the second harmonic generation (SHG) dynamics for metal spheres and nanorods - presented as multimedia files - is performed to reveal the dynamics of the modes supported by the nanostructure. We demonstrate that the interplay between different modes controls the nonlinear response and that the size-induced redshift of the eigenmodes can be manipulated by adjusting the nanostructure geometry, so that the SHG signal can be boosted at specified frequencies. We show that the SHG radiation is not necessarily quadrupolar in spherical nanoparticles, as it is often assumed. Finally, we introduce an efficient way to reduce the SHG calculation time.

Strong second-harmonic generation from Au-Al heterodimers.

Abstract: Second-harmonic generation (SHG) is investigated from three kinds of lithographically fabricated plasmonic systems: Al monomers, Au monomers and Au-Al heterodimers with nanogaps of 20 nm. Spectrally integrated SHG intensities and the linear optical responses are recorded and compared. The results show that for the monomer nanoantennas, the SHG signal depends sensitively on the linear excitation of the plasmon resonance by the fundamental wavelength. For Au-Al heterodimer nanoantennas, apart from fundamental resonant excitation, nonlinear optical factors such as SH driving fields and phase interferences need to be taken into account, which play significant roles at the excitation and scattering stages of SHG radiation. It is interesting to note that a possible energy transfer process could take place between the two constituting nanoparticles (NPs) in the Au-Al heterodimers. Excited at the linear plasmon resonance, the Au NP transfers the absorbed energy from the fundamental field to the nearby Al NP, which efficiently scatters SHG to the far-field, giving rise to an enhanced SHG intensity. The mechanisms reported here provide new approaches to boost the far-field SHG radiation by taking full advantage of strongly coupled plasmonic oscillations and the synergism from materials of different compositions.

Photocatalytic ammonia production enhanced by a plasmonic near-field and hot electrons originating from aluminium nanostructures.

Abstract: Ammonia production at room temperature and atmospheric pressure is in high demand to assist in energy saving and the protection of the environment worldwide, as well as to help reduce CO2 emissions. Recently, plasmonic nanomaterials have been frequently used for solar to chemical energy conversion, which has the potential to replace existing energy-intensive industrial processes. In our approach, plasmonic aluminium nanotriangles (AlNTs) were used to investigate the impact of plasmonic effects on photocatalytic ammonia production. Plasmonic near-field coupling to a semiconductor and hot electron generation from AlNTs were studied in detail through the use of electrochemical photocurrent measurements. A narrowband LED beam with a central wavelength at 365 nm was used to illuminate the AlNTs and their hot electron generation efficiency was estimated to be 2 × 10−4%, resulting in an ammonia production rate of 4 × 10−5 μM h−1 mW−1 cm−2, which corresponds to a quantum efficiency of 2.5 × 10−5%. In the case of plasmonic near-field coupling, AlNTs-embedded TiO2 demonstrates a charge-carrier generation efficiency of 2.7%, which is ∼2.3 times higher than that of bare TiO2. The ammonia production rate of AlNTs–TiO2 is 0.1 μM h−1 mW−1 cm−2 with a quantum efficiency of ∼0.06%, which corresponds to ∼2.4 times that of the rate demonstrated by bare TiO2 (0.04 μM h−1 mW−1 cm−2, quantum efficiency ∼ 0.025%). The obtained results confirm successful ammonia production through nitrogen splitting at room temperature and under atmospheric pressure. Moreover, according to the presented results, the use of plasmonic aluminium structures remarkably improves the ammonia production rate.

High-quality single crystal diamond diffraction gratings fabricated by crystallographic etching.

Abstract: We demonstrate a novel method for fabricating single crystal diamond diffraction gratings based on crystallographic etching that yields high-quality diffraction gratings from commercially available diamond plates. Both V-groove and rectangular gratings were fabricated and characterised using scanning electron microscopy and atomic force microscopy, revealing angles of 57° and 87° depending on the crystal orientation, with mean roughness below Ra = 5 nm on the sidewalls. The gratings were also optically characterised, showing good agreement with simulated results. The fabrication method demonstrated in this contribution shows the way for manufacturing high-quality diamond diffractive components that surpass existing devices both in quality and manufacturability.

Studying the different coupling regimes for a plasmonic particle in a plasmonic trap

Abstract: Plasmonic antennas improve the stiffness and resolution of optical tweezers by producing a strong near-field. When the antenna traps metallic objects, the optically-resonant object affects the near-field trap, and this interaction should be examined to estimate the optical force accurately. We study this effect in detail by evaluating the force using both Maxwell’s stress tensor and the dipole approximation. In spite of the strong optical interaction between the particle and the antenna, the results show that the dipole approximation remains accurate for calculating forces on Rayleigh particles. For particles whose sizes exceed the dipole limit, we observe different coupling regimes where the force becomes either attractive or repulsive. The distributions of field amplitudes and polarization charges explain such a behavior.

Quantifying Fano properties in self-assembled metamaterials

Abstract: Fano resonances in metamaterials can be explained by the coupling between different modes sustained by the meta-atom. While the associated spectral features are usually quite easy to identify for top-down metamaterials, thanks to the deterministic arrangement of the meta-atom relative to the illumination, the identification of spectral features due to Fano resonances is much more challenging for bottom-up metamaterials. There, the response is spurred by the random arrangement of the meta-atoms relative to the illumination. To improve the situation, we introduce a quantity that measures the nonorthogonality of the modes sustained by the meta-atom. The measure allows us to disclose whether specific details in the spectral response emerge from Fano features or whether they are only due to the incoherent superposition of different modes. We strengthen our argumentation while discussing the multipolar decomposition of the different modes that contribute to the Fano features for a representative meta-atom.

Surface-wave dispersion retrieval method and synthesis technique for bianisotropic metasurfaces

Abstract: We propose a surface-wave dispersion retrieval method and synthesis technique that applies to bianisotropic metasurfaces that are embedded in symmetric or asymmetric environments. Specifically, we use general zero-thickness sheet transition conditions to relate the propagation constants of surface-wave modes to the bianisotropic susceptibility components of the metasurface, which can themselves be directly related to its scattering parameters. It is then possible to either obtain the metasurface dispersion diagram from its known susceptibilities or, alternatively, compute the susceptibilities required to achieve a desired surface-wave propagation. The validity of the method is demonstrated by comparing its results to those obtained with exact dispersion relations of well known structures such as the propagation of surface plasmons on thin metallic films. In particular, this work reveals that it is possible to achieve surface-wave propagation only on one side of the metasurface either by superposition of symmetric and asymmetric modes in the case of anisotropic metasurfaces or by completely forbidding the existence of the surface wave on one side of the structure using bianisotropic metasurfaces.

When light explores space and time

Abstract: A commentary on the article “Uniform-velocity spacetime crystals” by Zoe-Lise Deck-Leger et al. in Advanced Photonics Volume 1, Issue 5.

Feature issue introduction: advanced computational nanophotonics: from materials to devices

Abstract: Computational nanophotonics has already made a disruptive impact on the photonic and optoelectronic industries and has dramatically influenced the ways today’s optical engineers create, optimize, and use innovative materials and computer-aided services. This Feature Issue presents a set of eleven papers combined under the joint title of Advanced Computational Nanophotonics: From Materials to Devices. The science and art of computational photonics have a long established history, yet interest in new approaches to advanced multiphysics modeling at the nanoscale and hence to innovatory multi-objective optimization techniques for nanophotonics have been growing exponentially in the last decade, and are now the subject of intense cross-disciplinary research efforts. The papers selected for the Feature Issue present a diverse palette of topics that, for example, include a comprehensive review of new optimization techniques, a fundamental theoretical concept of photonic Dirac monopoles, along with new multiphysics approaches to full-wave material modeling in non-linear nanophotonics and, in particular, to innovative modeling of photonic neural networks. Applications of advanced computational methods are additionally showcased with space-time light control by dynamic metasurfaces, polarization control with structured color all-dielectric metafilms, and an optofluidic system driven by a thermoplasmonic element.

Symmetries and Angular Scattering Properties of Metasurfaces

Abstract: We study the angular scattering behavior of bianisotropic metasurfaces and deduce relationships between the corresponding symmetrical angular scattering properties and the structural symmetries of their scattering particles. This may be of practical interest for the realization of metasurfaces with complex angular scattering characteristics.

Towards Efficient Nonlinear Plasmonic Metasurfaces

Abstract: Nonlinear processes are important in many fields of photonics ranging from biomedical imaging to ultrashort pulse generation. Progress in nanophotonics and metamaterials has created a growing demand for nanoscale nonlinear optical components. However, it is difficult to answer this demand by using traditional materials motivating the search for alternatives approaches. Nonlinear plasmonics has emerged as a viable solution for enabling efficient and nanoscale nonlinear optics. Despite steady progress, so far achieved conversion efficiencies of metamaterials have not yet rivalled conventional nonlinear materials. Here, we discuss our recent progress in development of efficient nonlinear plasmonic metamaterials. Focus is on metasurfaces utilizing collective responses known as surface lattice resonances, which can be used to dramatically boost nonlinear responses of metasurfaces.