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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) - Surface-Field Terahertz Emission Enhancement via 2D-Materials
摘要： Narrow-bandgap III-V semiconductors are proving to be excellent terahertz (THz) emitters when excited by ultrashort optical pulses. The specific nonlinear process contributing to the emission is inherently complicated by the fact that many different mechanisms contributing to the nonlinearity exist. Surface field surge currents, photo-Dember and third order surface field-seeded optical rectification (SOR) are the most commonly acknowledged source phenomena. SOR relies on the static electric field resulting from charges populating the material surface states, which is responsible for the band bending and formation of a depletion region at the interface. SOR in Indium Arsenide has been singled out as the dominant generation mechanism at high excitation energies. THz generation is typically limited by the saturation of the relevant field-matter interaction mechanism, the damaging threshold of nonlinear crystals or the lack of suitable phase matching between THz and optical fields in real materials. We have recently demonstrated that for SOR, the quadratic dependence between the emitted THz energy and the pump energy is re-established at extreme excitations. Increasing the impinging optical pump further, however, becomes impractical as the optical damage threshold of the semiconductor is approached. It would, therefore, be greatly beneficial to instead enhance the surface field to enable a continued increase in the emitted THz field.
关键词： 2D-materials,surface field enhancement,terahertz emission,semiconductors,graphene
更新于2025-09-12 10:27:22
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Optical Properties of Bowtie-Type Nanoantennas Integrated Onto a Silicon Waveguide Platform
摘要： In this paper, we provide a detailed three-dimensional numerical analysis of the optical properties of common and modified bowtie aperture antennas integrated onto a silicon waveguide platform, to discuss the influence of geometrical parameters on the electric field enhancement factor and waveguide transmission when such antennas are excited by the evanescent field of the Si waveguide mode. We demonstrate that waveguide transmission is severely affected by the interference between Si waveguide modes and surface plasmon polariton modes excited in the antenna, while the antenna’s field enhancement factor is mainly determined by the localized surface plasmon resonance occurring in its nano-gap. These mechanisms lead to a mismatch between the wavelength at which the antenna’s field enhancement factor is maximized, and the wavelength at which transmission through the Si waveguide is minimized, suggesting that in some multi-mode cases, the optical properties of integrated nanoantennas determined through direct measurement of Si waveguide transmission may be misleading. Methods for improving the electric field enhancement (such that it has a bigger modulation depth) that have minimal impact on the resonant wavelength, and for improving the shape and location of the corresponding hot spot of the bowtie aperture antennas, are also discussed and analyzed. We believe that this analysis will be helpful in design of on-chip bowtie-type optical antennas for surface enhanced Raman spectroscopy, near-field optical microscopy, high sensitivity detection, and plasmonic optical tweezers.
关键词： Bowtie aperture antenna,Transmission,Silicon waveguide platform,Electric field enhancement
更新于2025-09-11 14:15:04
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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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Complex-conjugate Pole-residue Pair-Based FDTD Method for Assessing Ultrafast Transient Plasmonic Near Field
摘要： The study of the optical properties of plasmonic nanostructures in the stationary regime has greatly benefited from the development of numerical methods, among which Finite Difference Time Domain (FDTD) is popular. In contrast, the use of these numerical tools for assessing the transient plasmonic optical response triggered by ultrashort laser pulses is hampered by the difficulty to address small variations of the material optical properties with reasonable computational time. Yet, many of the developments based on this ultrashort response rely on the dynamics of the near-field topography around the nanostructures. In this article, we present a way to bridge this gap with the complex-conjugate pole-residue pair (CCPRP) approach. A CCPRP-based FDTD simulator has been developed. First, a simple methodology to check the end-to-end accuracy of the FDTD simulation is provided. Then, in conjunction with a three-temperature model, the approach enables us to calculate the ultrafast transient near field inside and around a gold nanoparticle (AuNP) upon absorption of a subpicosecond laser pulse. The transient variation of the field intensity inside and around the AuNP is compared with the one determined by the Mie theory. The dependence of the transient field intensity on the distance away from the nanoparticle surface and on the delay time after laser pulse absorption is finally analyzed.
关键词： Ultrafast,Complex-conjugate pole-residue pairs,Nanoparticles,Plasmonics,Near-field enhancement,FDTD
更新于2025-09-11 14:15:04
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Tunable enhanced sensing of ferrite film using meander-shaped spoof surface plasmon polariton waveguide
摘要： In this letter, the magnetic field enhancement characteristics of the spoof surface plasmon polaritons (SSPPs) is utilized to enhance the sensing of thin ferrite film. The operating sensing frequency can be tuned by adjusting the bias static magnetic field. For demonstration, a magnetic yttrium iron garnet film (i.e., YIG) with small thickness of 2 μm over a simple SSPP-based sensing structure is designed, fabricated and measured, showing improvement of higher than 20 dB to the absorption (i.e., sensing ability). The proposed method has significant potentials in the application of plasmonic integrated devices using thin ferrite materials.
关键词： sensing,magnetic field enhancement,spoof surface plasmon polaritons,ferrite film,SSPPs
更新于2025-09-11 14:15:04
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Towards rational design and optimization of near-field enhancement and spectral tunability of hybrid core-shell plasmonic nanoprobes
摘要： In biology, sensing is a major driver of discovery. A principal challenge is to create a palette of probes that offer near single-molecule sensitivity and simultaneously enable multiplexed sensing and imaging in the “tissue-transparent” near-infrared region. Surface-enhanced Raman scattering and metal-enhanced fluorescence have shown substantial promise in addressing this need. Here, we theorize a rational design and optimization strategy to generate nanostructured probes that combine distinct plasmonic materials sandwiching a dielectric layer in a multilayer core shell configuration. The lower energy resonance peak in this multi-resonant construct is found to be highly tunable from visible to the near-IR region. Such a configuration also allows substantially higher near-field enhancement, compared to a classical core-shell nanoparticle that possesses a single metallic shell, by exploiting the differential coupling between the two core-shell interfaces. Combining such structures in a dimer configuration, which remains largely unexplored at this time, offers significant opportunities not only for near-field enhancement but also for multiplexed sensing via the (otherwise unavailable) higher order resonance modes. Together, these theoretical calculations open the door for employing such hybrid multi-layered structures, which combine facile spectral tunability with ultrahigh sensitivity, for biomolecular sensing.
关键词： plasmonic nanoprobes,near-field enhancement,hybrid core-shell,biomolecular sensing,spectral tunability,multiplexed sensing
更新于2025-09-11 14:15:04
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Electromagnetic Energy Redistribution in Coupled Chiral Particle Chain-Film System
摘要： Metal nanoparticle-film system has been proved that it has the ability of focusing light in the gap between particle and film, which is useful for surface-enhanced Raman scattering and plasmon catalysis. The rapid developed plasmonic chirality can also be realized in such system. Here, we investigated an electromagnetic energy focusing effect and chiral near-field enhancement in a coupled chiral particle chain on gold film. It shows large electric field enhancement in the gap between particle and film, as well as chiral near field. The enhancement properties at resonant peaks for the system excited by left circularly polarized light and right circularly polarized light are obviously different. This difference resulted from the interaction of circularly polarized light and the chiral particle-film system is analyzed with plasmon hybridization. The enhanced optical activity can provide promising applications for the enhancement of chiral molecule sensor for this chiral particle chain-film system.
关键词： Chiral near-field enhancement,Chiral plasmonic nanostructures,Chiral focusing,Electromagnetic energy focusing
更新于2025-09-11 14:15:04
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Photonic Microcavity-Enhanced Magnetic Plasmon Resonance of Metamaterials for Sensing Applications
摘要： We investigate photonic microcavity-enhanced magnetic plasmon (MP) resonance in metamaterials for high-quality refractive index sensing. The metamaterials are consisting of a top periodic array of U-shaped metallic split-ring resonators (SRRs), a middle dielectric layer, and a bottom metallic backed plate. The top metallic SRRs that are placed at about Bragg distance above the bottom metallic plate constitute a photonic microcavity. Because the MP resonance excited in metallic SRRs is coupled to the photonic microcavity mode supported by the photonic microcavity, the radiative damping of the MP resonance is strongly reduced and consequently its linewidth is decreased dramatically. Benefiting from the narrow linewidth, large modulation depth, and giant magnetic field enhancement at the MP resonance, the cavity-coupled metamaterial sensor has very high sensitivity (S =400 nm/RIU, S* =26/RIU) and figure of merit (FOM =33, FOM* =4215), which suggests that the proposed metamaterials have potential in applications of plasmonic biosensors.
关键词： Optical sensing and sensors,Narrow linewidth,Magnetic field enhancement,Photonic microcavity,Metamaterials
更新于2025-09-10 09:29:36
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The Remote Light Emission Modulated by Local Surface Plasmon Resonance for the CdSe NW-Au NP Hybrid Structure
摘要： CdSe nanowire (NW)–Au nanoparticle (NP) compounds are synthesized successfully using the method of physical vapor deposition, and the modulated remote emission is realized in the hybrid structure with strong metal–semiconductor coupling. The well-crystallized, uniform morphology, smooth surface CdSe NW is attached with an Au NP on the terminal, which forms the integration structure with direct plasmon–exciton coupling of semiconductor–metal hybrid system. When the CdSe terminal or Au NP terminal of the hybrid structure is excited by the laser with wavelength of 633 nm, the remote light emission at another terminal is greatly modulated. To reveal the physical mechanism of energy conviction between plasmon and exciton, finite-difference time-domain simulations are performed for the CdSe NW–Au NP hybrid structures. The calculated results confirm that the modulation of remote light emission is attributed to the competing of the quench of photoluminescence and the electric field enhancement of local surface plasmon resonance. These works can provide deeper understanding of physical mechanism of plasmon and exciton coupling, and open up new application for the remote light sensing and detection.
关键词： localized electromagnetic field enhancement,remote light emission,CdSe NW,Au NP,photoluminescence
更新于2025-09-10 09:29:36
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Deterministic Arrays of Epitaxially Grown Diamond Nanopyramid <i>s</i> with Embedded Silicon-Vacancy Centers
摘要： The negatively charged silicon-vacancy center (SiV) in diamond is a potential high-quality source of single-indistinguishable photons for quantum information processing and quantum electrodynamics applications. However, when embedded in bulk diamond, this emitter suffers from both, relatively low extraction efficiency attributed to total internal reflection as well as nondeterministic location. On the other hand, its implementation in nanodiamonds is impeded by optical dephasing owing to their degraded surface quality. Here a robust and deterministic template-assisted bottom-up process for the creation of high-quality diamond nanopyramids incorporating SiVs is reported. This method employs a predefinition of high-precision nanopillars by e-beam lithography and dry etching, and subsequent epitaxial overgrowth during which Si atoms are introduced into diamond. The overgrown layer, including the nanopyramid arrays, is epitaxial as confirmed by comprehensive analyses. This diamond nanopyramid, hosting the SiVs, can pave the way toward efficient localized single-photon source arrays and potentially outshine nanodiamonds and nanosized structures prepared by a top-down method. The lateral confinement of the SiVs inside the deterministic nanosized pyramids enables their positioning at the center of cavities and optical structures for enhanced quantum efficiency and light–matter manipulation, and their employment as a system to explore collective coherent interactions between ensembles and confined light.
关键词： nanopyramids,field enhancement,spatial addressing,silicon-vacancy centers,diamond
更新于2025-09-10 09:29:36