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Plasma and Plasmonics || 7 Advanced Topics in Plasmonics
摘要： As the name suggests, NIMs are materials which have a negative index of refraction and were first proposed by V. G. Veselago in 1968 [24]. These materials are not naturally occurring but are artificially constructed using ideas similar to that used in the generation of spoof surface plasmon (SSP) waves discussed in Chapter 6. The refractive index of a material is given by n = √(?rμr), where ?r is the relative permittivity and μr is the relative permeability of the material. For naturally occurring materials, ?r and μr are usually positive for most frequencies. However, as was discussed in Chapter 2, the permittivity of metals can become negative for some range of frequency near the visible spectrum. As shown in Chapter 6, we can mimic this negative permittivity behavior at much lower frequencies by drilling holes in the metal surface with an appropriate hole size and array size. In these cases, the permeability of the material is still positive, and hence the refractive index is imaginary. Due to this regular electromagnetic waves cannot travel inside the medium and all we have are surface plasmon waves. However, if we could make both the permittivity and permeability negative for the same frequency range, the product ?rμr will again be positive and hence the refractive index will be a real quantity. Such materials are also called double negative metamaterials (DNGs). In this case, we choose the negative sign for n to distinguish it from the usual case when ?r and μr are positive. When the refractive index is real, we again have regular electromagnetic waves traveling through the medium but some of the properties of wave propagation in NIMs are very intriguing and very different from the case of Positive Index Materials (PIMs). NIMs have several applications, the primary among them being the superlens which can allow imaging beyond the diffraction limit. Other applications include metamaterial antennas which can help in miniaturization of transmitting devices, optical nanolithography and nanotechnology circuitry.
关键词： Plasmonics,NIMs,SERS,Negative Index Metamaterials,Surface-Enhanced Raman Scattering,Particle Traps
更新于2025-09-16 10:30:52
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Optical properties of laser-modified diamond: From visible to microwave range
摘要： We have measured the optical properties of a graphitised layer with dc conductivity of 305 W–1 cm–1 produced by excimer laser irradiation (KrF, t = 20 ns, l = 248 nm) of a polycrystalline diamond surface grown by chemical vapour deposition. Studies have been conducted in a wide range of wavelengths: from far-IR to visible spectral regions. The resulting constants of the Drude model are the basic parameters for calculating the electromagnetic response of diamond/graphite photon elements or metamaterials fabricated using the direct laser writing method.
关键词： optical properties,diamond,metamaterials,spectroscopy,nanocrystalline graphite,laser
更新于2025-09-16 10:30:52
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Ultrathin Wetting Layer-Free Plasmonic Gold Films
摘要： Ultrathin gold films are attractive for plasmonic and metamaterial devices, thanks to their useful optical and optoelectronic properties. However, deposition of ultrathin continuous Au films of few nanometer thickness is challenging and generally requires wetting layers, resulting in increased optical losses and incompatibility with optoelectronic device requirements. We demonstrate wetting layer-free plasmonic gold films with thicknesses down to 3 nm obtained by deposition on substrates cooled to cryogenic temperatures. We systematically study the effect of substrate temperature on the properties of the deposited Au films, and show that substrate cooling suppresses the Vomer-Webber growth mode of Au, promoting early-stage formation of continuous Au films with improved surface morphology and enhanced optoelectronic properties. Our results pave the way for straightforward implementation of ultrathin Au-based optoelectronic and plasmonic devices, as well as metamaterials and metasurfaces.
关键词： metamaterials,cryogenic deposition,plasmonics,thin films,gold
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - To the Treatment of Anterior Uveitis
摘要： We investigate terahertz quantum cascade lasers with a dense array of active micropillars forming the gain medium. Depending on the size of these pillars relative to the emission wavelength different optical regimes are identified. For pillar dimensions on the order of the emission wavelength, a photonic crystal resonator is created. Single mode emission is observed at high symmetry points of the photonic band structure. The selection mechanism of the favored laser mode is studied by analyzing the gain enhancement effect for eigenmodes with a low group velocity and a large mode confinement of the electric field energy in the micropillars. Subwavelength micropillar arrays constitute a photonic metamaterial, which can be described using an effective medium approximation. Similar to a bulk laser ridge, the array forms a Fabry–Pérot resonator that is defined by the boundaries of the array. From the longitudinal mode spacing, we derive an effective group index of the pillar medium. Limitations in terms of minimum filling factors and waveguide losses for the realization of subwavelength micropillar and nanowire array terahertz quantum cascade lasers are investigated.
关键词： Photonic crystals,terahertz,optical waveguides,optical metamaterials,quantum cascade lasers
更新于2025-09-16 10:30:52
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Multiple scattering enabled superdirectivity from a subwavelength ensemble of resonators
摘要： An ensemble of resonators arranged on a subwavelength scale is usually considered as a bulk effective medium, known as a metamaterial, and can offer unusual macroscopic properties. Here, we take a different approach and limit ourselves to the study of only a few number of such elementary components and demonstrate that they still offer uncommon opportunities. Typically, owing to the multiple scattering and the phase shift that the resonances offer, we observe ?elds that vary at scales completely independent of the wavelength in free space. By smartly tuning the resonance frequencies, we can design at will the complex current distribution in those resonators. This way, we design a superdirective antenna, i.e., an antenna that is surprisingly more directive than its size would foreshadow. This approach is veri?ed numerically and experimentally in the context of microwaves, but this applies to any wave ?eld where subwavelength resonators exist.
关键词： metamaterials,superdirectivity,microwaves,subwavelength resonators,multiple scattering
更新于2025-09-16 10:30:52
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Fast Analysis of Metasurfaces through Temporal Coupled-mode Theory
摘要： In this article, a rigorous temporal coupled-mode theory (CMT) formalism is developed, to analyze metasurface (MTS)-based structures. Such MTSs are generally rather complex, requiring extensive, full-wave simulations. To facilitate their design and minimize the associated computational demand, the CMT solves a small linear system of equations, fed by the results of certain much simpler and less time- and memory-consuming eigenvalue problems. The proposed method is versatile and offers an initial, valuable estimation of the structure’s frequency response, which may be used as a guideline for the ?nal MTS ?ne tuning. As proof of concept, split-ring resonator (SRR) MTSs coupled to microstrip lines are analyzed, and their response is compared with the full-wave ?nite-element method (FEM) results.
关键词： Coupled-mode analysis,planar arrays,metasurfaces (MTSs),electromagnetic metamaterials
更新于2025-09-16 10:30:52
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Active digital spoof plasmonics
摘要： Digital coding and digital modulation are the foundation of modern information science. Combination of the digital technology with metamaterials provides a powerful scheme for spatial and temporal controls of electromagnetic waves. Such a technique, however, has thus far been limited to the control of free-space light. Its application to plasmonics to shape subwavelength fields still remains elusive. Here, we report the design and experimental realization of a tunable conformal plasmonic metasurface, which is capable of digitally coding and modulating designer surface plasmons at the deep subwavelength scale. Based on dynamical switching between two discrete dispersion states in a controlled manner, we achieve digital modulations of both amplitude and phase of surface waves with nearly 100% modulation depth on a single device. Our study not only introduces a new approach for active dispersion engineering, but also constitutes an important step towards the realization of subwavelength integrated plasmonic circuits.
关键词： plasmonics,digital coding,digital metamaterials,digital modulation
更新于2025-09-16 10:30:52
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Plasmonic Metamaterials for Nanochemistry and Sensing
摘要： Plasmonic nanostructures were initially developed for sensing and nanophotonic applications but, recently, have shown great promise in chemistry, optoelectronics, and nonlinear optics. While smooth plasmonic films, supporting surface plasmon polaritons, and individual nanostructures, featuring localized surface plasmons, are easy to fabricate and use, the assemblies of nanostructures in optical antennas and metamaterials provide many additional advantages related to the engineering of the mode structure (and thus, optical resonances in the given spectral range), field enhancement, and local density of optical states required to control electronic and photonic interactions. Focusing on two of the many applications of plasmonic metamaterials, in this Account, we review our work on the sensing and nanochemistry applications of metamaterials based on the assemblies of plasmonic nanorods under optical, as well as electronic interrogation.
关键词： field enhancement,sensing,localized surface plasmons,optical antennas,nanochemistry,optical resonances,electronic interrogation,surface plasmon polaritons,metamaterials,Plasmonic nanostructures
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) - Coherent Control of the Non-Instantaneous Response of Plasmonic Nanostructes
摘要： Nonlinear metamaterials have revolutionized nonlinear optics, allowing novel abilities that expand the current available nonlinear material capabilities. Due to their unique response, nanoparticles (NP's) have been the subject of research in numerous fields ranging from physics, engineering, biology, medicine and others. Understanding their physical mechanism and properties has enabled unprecedented capabilities in linear and nonlinear optics, sensing, theragnostic biomedical optics, material classifications of molecular structures as complicated as DNA or sensitive as oxygen singlets and much more [1-4]. A complete theoretical description, based on the nonlinear scattering theory, has been found suitable to describe the geometrical contribution of nanostructures (NSs) to their nonlinear response [5]. Yet, until now, a comprehensive theory has been investigated only for the instantaneous nonlinear response. A full response, including the resonant non-instantaneous behavior brought about by their resonant linewidth, has not yet been studied. We experientially demonstrate variance in the nonlinear response by coherently controlling the electric field. We show, for the first time to our knowledge, resonant non-instantaneous properties by coherent control measurements of nonlinear second harmonic generation (SHG) in resonant media. (see Figure 1). In contrary to common perception, we find that transform limited pulses do not yield the strongest nonlinearity in SHG. Approaching strong fields, a decrease in nonlinear behavior is not captures in traditional nonlinear models. We develop a theoretical framework, analogous to a resonant 3 level interaction, capturing non-instantaneous resonant phenomena portraying resonant effects beyond the weak field two-photon description. These include deviations from the conventional SHG nonlinearity which commonly is proportional to the square of the fundamental field intensity (see Figure 2.a). We also show that with changing the localized surface plasmonic resonant wavelength relative to the source's central wavelength, a shift in energy distribution and intensity emerges in the SH process pointing to the relative position of the resonant frequency (see Figure 2.b).
关键词： Nonlinear metamaterials,nanoparticles,second harmonic generation,nonlinear optics,plasmonic nanostructures
更新于2025-09-12 10:27:22
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Dual-band electromagnetically induced transparency effect in asymmetrically coupled terahertz metamaterials
摘要： In this article, we numerically and experimentally investigate a metamaterial geometry capable of exhibiting dual-band electromagnetic induced transparency (EIT) effect in terahertz frequency regime. The meta-molecule unit consists of two asymmetric C resonators, placed alternately on both sides of a cut-wire (CW). The near field coupling between the CW and C resonators of the MM structure leads to the evolution of the dual-band EIT effect. We observe that the dual-band EIT effect can be modulated by changing the distance between the CW and the 2C resonators. Our study can play an important role in the development of multi-band slow light devices, modulators and also for sensing applications.
关键词： sensing,modulators,slow light devices,metamaterials,dual-band electromagnetically induced transparency,terahertz
更新于2025-09-12 10:27:22