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Negative Refraction in Time-Varying Strongly Coupled Plasmonic-Antennaa??Epsilon-Near-Zero Systems
摘要： Time-varying metasurfaces are emerging as a powerful instrument for the dynamical control of the electromagnetic properties of a propagating wave. Here we demonstrate an efficient time-varying metasurface based on plasmonic nano-antennas strongly coupled to an epsilon-near-zero (ENZ) deeply subwavelength film. The plasmonic resonance of the metal resonators strongly interacts with the optical ENZ modes, providing a Rabi level spitting of ～30%. Optical pumping at frequency ω induces a nonlinear polarization oscillating at 2ω responsible for an efficient generation of a phase conjugate and a negative refracted beam with a conversion efficiency that is more than 4 orders of magnitude greater compared to the bare ENZ film. The introduction of a strongly coupled plasmonic system therefore provides a simple and effective route towards the implementation of ENZ physics at the nanoscale.
关键词： time-varying metasurfaces,epsilon-near-zero,plasmonic nano-antennas,negative refraction,phase conjugation
更新于2025-09-19 17:13:59
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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) - Scanning Resonant Nano-Antenna High Resolution Imaging and Emission Control of hBN Defect Photon Emission
摘要： Single atomic defects in hexagonal boron nitride (hBN) are particularly interesting due to their stability of emission and absence of blinking and bleaching, at ambient conditions. Furthermore, they show exceptional robustness of emission, even at high temperatures of operation. Therefore, hBN defects have emerged as promising candidates for novel robust single photon sources. Several attempts have been done to induce hBN defects in a controlled manner. Because of their ease of accessibility and, due to the nanometer scale thickness of the hBN flakes, these defects are attractive to couple to plasmonic structures in order to increase their photon emission. However efficient coupling requires a high precision of positioning (<20 nm) and so far the methods adopted lack this level of control, both in assembling and imaging. Also, they present static configurations of coupled emitter-particles and no strategy is adopted in order to discern between the photons emitted by the hBN defects and the luminescence of the metallic particles. Here we present first systematic and simultaneous coupling and imaging of hBN emission centers with resonant optical antennas, with nanometer control and optical resolution of 45 nm. We show the capability of nano-antennas to manipulate hBN defects by depleting their emission 30-70%. Our setup is a near-field microscope working in scattering configuration, where we fabricate a single dipolar nano-antenna as a near-field probe that we can independently scan over hBN defects controlling the coupling and the fluorescence emission with nanometer resolution. We employ a photon time-gating technique in order to discriminate the light emitted by the metallic antenna by the one radiated by the hBN emitters. Finally, we report on a lifetime shortening of 2x, due to coupling emitter--antenna.
关键词： nano-antennas,single photon sources,plasmonic structures,near-field microscope,hBN defects
更新于2025-09-16 10:30:52
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A Comparative Investigation of Plasmonic Properties between Tunable Nanoobjects and Metallized Nanoprobes for Optical Spectroscopy
摘要： In order to evaluate the optical efficiency of tip-based probes for future tip-enhanced optical spectroscopy applications, we have developed an experimental setup based on the coupling of an achromatic inverted microscope equipped with a total internal reflection objective and an atomic force microscopy (AFM) head. This spectroscopic tool has been validated using individual nanofabricated antennas (gold nanodisks/nanocones) on a glass substrate, which act as nanoresonators based on localized surface plasmons. Spectrally tunable transverse electric and magnetic plasmonic resonances are identified and are in excellent agreement with numerical calculations performed as a function of the nano-antenna geometry and size. We have investigated a series of state-of-the-art gold-coated AFM probes, which are commonly used for tip-enhanced (Raman spectroscopy) optical experiments. Their scattering spectrum consists of resonances depending on the tip sharpness or granularity superimposed on a broad emission spectrum due to semi-infinite metal layer acting as a non-resonant antenna. From the comparison between the plasmonic response of both types of optical antennas, a new generation of probes for tip-enhanced optical spectroscopy is proposed, in which single plasmonic nano-antennas are engineered at the apex of a non-metallic AFM tip. As from numerical simulation results, such tips would ensure a spectral tunability as a function of the material, size, and geometry, together with expected high enhancement factors. Such features would allow the design of spectrally tunable surface enhanced Raman spectroscopy substrates, and should be a reliable and efficient alternative to tips commonly used in tip-enhanced optical spectroscopy experiments such as tip-enhanced Raman spectroscopy.
关键词： Optical Spectroscopy,Plasmonics,TERS,Nano-antennas,AFM
更新于2025-09-12 10:27:22
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Enhanced light-matter interaction in an atomically thin semiconductor coupled with dielectric nano-antennas
摘要： Unique structural and optical properties of atomically thin two-dimensional semiconducting transition metal dichalcogenides enable in principle their efficient coupling to photonic cavities having the optical mode volume close to or below the diffraction limit. Recently, it has become possible to make all-dielectric nano-cavities with reduced mode volumes and negligible non-radiative losses. Here, we realise low-loss high-refractive-index dielectric gallium phosphide (GaP) nano-antennas with small mode volumes coupled to atomic mono- and bilayers of WSe2. We observe a photoluminescence enhancement exceeding 104 compared with WSe2 placed on planar GaP, and trace its origin to a combination of enhancement of the spontaneous emission rate, favourable modification of the photoluminescence directionality and enhanced optical excitation efficiency. A further effect of the coupling is observed in the photoluminescence polarisation dependence and in the Raman scattering signal enhancement exceeding 103. Our findings reveal dielectric nano-antennas as a promising platform for engineering light-matter coupling in two-dimensional semiconductors.
关键词： atomically thin semiconductor,light-matter interaction,Raman scattering,dielectric nano-antennas,photoluminescence enhancement
更新于2025-09-12 10:27:22
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Plasmonic Nano-antenna Optimization Using Characteristic Mode Analysis
摘要： Plasmonic nano-antennas are typically designed with RF-inspired rigorous parametric optimization processes that lack proper physical insights. In this study, we demonstrate a systematic optimization approach for nano-antennas based on characteristic mode analysis (CMA). A complex geometry, designated as split-ring two-wire antenna (SRA), is selected and optimized using the CMA technique. CMA identifies the dominant modes of the structure at the frequency of interest as well as explains the dependency of the modes on the structure’s shape, size and material properties. These insights from CMA have been used in the present study to efficiently optimize SRA shape, size, and material which yield more than 700 % near-field intensity enhancement (NFIE) at the desired operating frequency. This proposed CMA based optimization method can be adapted easily for many other nano-antenna applications, facilitating the development of improved nano-structures.
关键词： Split-ring Two-wire Antenna (SRA),Method of Moments (MOM),Plasmonic,Nano-structures / Nano-antennas,Near Field Intensity Enhancement (NFIE),Surface Integral Equation (SIE),Characteristic Mode Analysis (CMA)
更新于2025-09-11 14:15:04
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Colloidal Plasmonic Nanostar Antennas with Wide Range Resonance Tunability
摘要： Gold nanostars display exceptional field enhancement properties and tunable resonant modes that can be leveraged to create effective imaging tags, phototherapeutic agents, and hot electron-based photocatalytic platforms. Despite having emerged as the cornerstone among plasmonic nanoparticles with respect to resonant strength and tunability, some well-known limitations have hampered their technological implementation. Herein we tackle these recognized intrinsic weaknesses, which stem from the complex, and thus computationally untreatable, morphology and the limited sample monodispersity, by proposing a novel 6-spike nanostar, which we have computationally studied and synthetically realized, as the epitome of 3D plasmonic nanoantenna with wide range plasmonic tunability. Our concerted computational and experimental effort shows that these nanostars combine the unique advantages of nanostructures fabricated from the top-down and those synthesized from the bottom-up, showcasing a unique plasmonic response that remains largely unaltered in going from the single particle to the ensemble. Furthermore, they display multiple, well-separated, narrow resonances, the most intense of which extends in space much farther than observed before for any plasmonic mode localized around a colloidal nanostructure. Importantly, the unique close correlation between morphology and plasmonic response leads the resonant modes of these particles to be tunable between 600 and 2000 nm, a unique feature that could find relevance in cutting edge technological applications.
关键词： 3D nano-antennas,colloidal nanostars,plasmon tunability,localized surface plasmon resonances,EELS
更新于2025-09-11 14:15:04