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Self-Organized Nanorod Arrays for Large-Area Surface Enhanced Infrared Absorption
摘要： Highly sensitive Surface Enhanced Infrared Absorption (SEIRA) spectroscopy capabilities are demonstrated by exploiting large-area templates (cm2) based on self-organized (SO) nanorod antennas. We engineered highly dense arrays of gold nanorod antennas featuring polarization-sensitive localized plasmon resonances, tunable over a broadband near- and mid-infrared (IR) spectrum, in overlap with the so called ‘functional group’ window. We demonstrate polarization-sensitive SEIRA activity, homogenous over macroscopic areas and stable in time, by exploiting prototype self-assembled monolayers of IR-active octadecanthiol (ODT) molecules. The strong coupling between the plasmonic excitation and the molecular stretching modes give rise to characteristic Fano resonances in SEIRA. The SO engineering of the active hot-spots in the arrays allows to achieve signal amplitude improved up to the 5.7 %. This figure is competitive to the response of lithographic nanoantennas and is stable when the optical excitation spot varies from the micro- to the macroscale, thus enabling highly sensitive SEIRA spectroscopy on cost-effective nanosensor devices.
关键词： IR spectroscopy,large area nanosensors,Surface Enhanced Infra-Red Absorption (SEIRA),self-organized arrays,Fano resonances,Plasmonic nanoantennas
更新于2025-09-23 15:19:57
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Application of Plasmonic Nanoantennas in Enhancing the Efficiency of Organic Solar Cells
摘要： It is known that the periodic use of silver nanoantennas in organic solar cells increases the e?ciency of light absorption. In this study, we performed a geometric parametric analysis of nanoantennas using the ?nite element method. Based on the study of the convex truncated cone nanoantenna, we have found that a nanoantenna arrangement formed by the convex truncated cone nanoantenna along with a pyramidal nanoantenna provides a better solution for di?erent angles of light incidence compared to a single nanoantenna. We obtained a mean increase in the absorption e?ciency of this organic solar cell, both for the TM and TE polarizations, compared to the use of the conventional nanoantenna in the wavelength range of 300–800 nm.
关键词： convex truncated cone nanoantenna,organic solar cells,finite element method,pyramidal nanoantenna,plasmonic nanoantennas,light absorption
更新于2025-09-23 15:19:57
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Weak superradiance in arrays of plasmonic nanoantennas
摘要： A collection of N emitters can exhibit an N-fold broadening of the radiative linewidth resulting from the development of a macroscopic dipole moment. Such a broadening of the radiative linewidth has previously been observed in systems of several nanoparticles and has often been described in terms of superradiant behavior. However, the understanding of the physics behind the observed dependence of radiative linewidth on the number of irradiated nanoparticles is far from complete. In this paper, we present theoretical and experimental results that elucidate this broadening mechanism in plasmonic systems and draw a connection with the phenomenon of Dicke superradiance. We demonstrate that, in the limit where radiative broadening dominates, the extinction linewidth of a planar array of plasmonic nanoantennas scales linearly with the number of nanoantennas contained within a circle of radius equal to the resonant optical wavelength. We explain this classical phenomenon as a weak superradiance effect, which corresponds to the case in the Dicke model where only the ground state and the first collective excited state contribute to the enhanced radiation.
关键词： superradiance,radiative linewidth,Dicke model,plasmonic nanoantennas,collective behavior
更新于2025-09-16 10:30:52
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Integrated Plasmonic Nanoantenna Gratings for Large Area Coherent Optical Source
摘要： The emission of coherent light from a large area with a controlled directivity is required for high quality holographic system. In application domains like automotive, such a source needs to be fully planar for compactness and portability. It can be made of discretized sub-sources as long as they remain coherent and with the same directivity. We have considered here an array of connected waveguides covering the surface of a glass substrate. These waveguides spread the laser light out on the whole surface. Discretized plasmonic nanoantennas positioned at specific locations along the waveguides realise then the out-of-plane coherent beam steering.
关键词： plasmonic nanoantennas,waveguide,beam steering,coherent optical source,holographic system
更新于2025-09-12 10:27:22
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Entanglement of bright and dark modes in parity-time-symmetric plasmonic nanoantennas
摘要： The generic model of two coupled multimode plasmonic nanospheres with gain and loss forming a parity-time (PT ) symmetric dimer is considered. Analytical solutions based on a quasistatic approximation are used to explore the behavior of the eigenmodes in such a coupled nanoantenna system as a function of their separation distances and their gain-loss level. It is shown that the introduction of the same amount of gain and loss modi?es the composition of eigenmodes and breaks their orthogonality. The resulting entanglement of different spatial order and symmetry modes can be advantageously exploited to actively control the scattering properties of such multimode PT -symmetric nanoantennas.
关键词： eigenmodes,gain and loss,plasmonic nanoantennas,quasistatic approximation,parity-time symmetry
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Antenna Tapering Strategy for Near-Field Enhancement Optimization in Terahertz Gold Nanocavities
摘要： Plasmonic nanoantennas (NAs) have received a growing attention in recent years due to their ability to confine light on sub-wavelength dimensions. More recently, this property has been exploited in the terahertz (THz) frequency range (0.1-10 THz) for enhanced sensing and spectroscopy, as well as for more fundamental investigations. These applications typically require high local electric fields that can be achieved by concentrating THz radiation into deeply sub-wavelength volumes located at the NAs extremities. However, the achievable near-field enhancement values are severely limited by the poor resonance quality factor of traditional rod-shaped THz NAs. Unlike what is commonly assumed in the infrared domain, here we show that an optimal NA tapering angle can be effectively introduced to obtain higher quality factors and, at least, twofold higher local near-field enhancement in comparison with standard (wire-like) dipolar THz NAs. To evaluate how the tapering angle affects the NA performance, a simplified quasi-analytical model was first developed. Each NA is considered as a truncated cone constituted by a sequence of gold cylinders of increasing radii, so that the effective refractive index of the surface mode propagating along the NA changes gradually along the main axis. Once the reflection coefficients for the surface mode at both extremities are retrieved, a NA can be interpreted as a Fabry-Perot resonator and its resonances can be analytically calculated. This model reveals a trade-off between large tapering angles (resulting in a low reflection coefficient at the large extremity) compared to small tapers (which are affected by high propagation losses for the surface mode), leading to an optimal taper angle. FEM-based simulations (COMSOL Multiphysics) were then used to confirm this prediction. 60-nm-thick gold tapered NA dimers were designed with 45-μm-long arms (in order to resonate at around 1 THz) and with their facing tips (100-nm-wide) separated by a 30 nm gap, thus realizing a bowtie geometry. We numerically investigated the near-field enhancement in the gap between the NAs, varying the tapering angle α from 0° to 10°. We found that in planar gold NA dimers the near field grows as the tapering angle increases up to α = 3.4°, where the maximum is reached. In order to experimentally confirm these results, arrays of gold tapered NA dimers were fabricated by electron beam lithography on a high resistivity silicon substrate. A transmission characterization by means of THz time-domain (far-field) spectroscopy was then carried out on the fabricated NA arrays revealing, as expected, an increase of the resonance quality factor for the optimized tapered geometry. In conclusion, we demonstrated an effective, yet simple, way to further boost and engineer the local field enhancement of THz NAs.
关键词： Plasmonic nanoantennas,tapering angle,near-field enhancement,quality factor,terahertz
更新于2025-09-11 14:15:04
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Phase control of plasmon enhanced two-photon photoluminescence in resonant gold nanoantennas
摘要： Plasmonic nanoantennas emit two-photon photoluminescence, which is much stronger than their second harmonic generation. Unfortunately, luminescence is an incoherent process and therefore generally not explored for nanoscale coherent control of the antenna response. Here, we demonstrate that, in resonant gold nanoantennas, the two-photon absorption process can be coherent, provided that the excitation pulse duration is shorter than the dephasing time of plasmon mode oscillation. Exploiting this coherent response, we show the pure spectral phase control of resonant gold nanoantennas, with effective read-out of the two-photon photoluminescence.
关键词： two-photon photoluminescence,gold nanoantennas,plasmonic nanoantennas,spectral phase control,coherent control
更新于2025-09-10 09:29:36