Abstract Topological photonics has attracted extensive attention, since it allows for a platform to explore and exploit versatile nano-optics systems. In particular, the ideal Weyl metamaterials have recently been demonstrated with fascinating phenomena such as chiral zero mode and negative refraction. In this work, we apply the photonic Weyl metamateirals into the optical tweezers. Based on the effective medium approach, the optical force generated by the body state of the Weyl metamaterial is systematically investigated. Interestingly, theoretical results show that for oblique incidence, the optical force spectra present a valley around Weyl frequency with zero magnitude exactly at the Weyl frequency, and the forces show strong optical circular dichroism. In addition, due to the bi-anisotropic properties, transmissions through the Weyl metamaterial exhibit a significant linear-to-circular polarization conversion and the transmitted wavefront acquires spin momenta of photons, which induces abnormal force on chiral particles. Our study may provide potential applications in the optical manipulations, polarization conversions, and wavefront engineering optics.
We present a wideband metamaterial (MM) filter based on a metal-dielectric-metal (MDM) structure. The proposed structure consists of a quartz dielectric substrate and two metallic square-loop arrays, which were deposited on both surfaces of the substrate. The performance of the proposed design was numerically simulated by considering the angle of incidence. The surface current and electric field distributions were calculated for the two resonant frequencies to examine the intrinsic mechanism of the proposed filter. The transmittance of the structure for various oblique angles of incidence was also analyzed. It is generally challenging to completely align the two metallic layers due to limitations in the manufacturing process. Hence, the influence of periodic misalignment on wave propagation was studied. Furthermore, a prototype of the proposed structure was fabricated and the transmission spectra were measured. Simulation and experimental results reveal that our proposed filter can achieve wideband transmission in the F-band. This work is valuable for the design of broadband filters in millimeter and terahertz waves.
A sandwich structured left-handed metamaterial (LHM) based on a silver dendritic cell array is prepared by using a double template-assisted electrochemical deposition method. This bottom-up approach provides a facile, lower-cost method to fabricate LHMs of larger areas at IR and even visible light frequencies.
In this paper, through a vector-spherical harmonics approach, we investigate the optical spectra of plasmonic Au nanoparticles excited by two special accelerating beams: a non-paraxial Airy beam and a Bessel beam. We systematically analyze the impacts of the beam profile, phase, and helical wave front of the electromagnetic fields on the optical spectrum and the excitation of the surface plasmon resonance (SPR). We find that the high-order phase in the Airy beam would result in strong plasmonic oscillations in the optical spectra, while the cone angle and orbital angular momentum carried by the Bessel beam could be employed to engineer the plasmon modes excited in Au nanoparticles. Furthermore, the optical spectrum excited by a combined Airy?Bessel?Gauss beam is discussed. The study could help to deeply explore new ways to manipulate SPR in metal nanoparticles via the wave front engineering of optical beams for enhancing light?matter interaction and optical sensing performance.
In this paper, we investigate the optical forces exerted on a graphene-coated dielectric particle by the Gaussian beam transmitted through the prism setup systematically. It is shown that the optical force spectra exhibit significant Fano resonance under the excitation of a Gaussian evanescent wave. The magnitude and morphology of Fano resonance can be modulated effectively by the graphene coating. Also, the modification on the threshold of the Fermi energy of graphene could help to regulate the trapping behavior efficiently. The proposed work may provide a new avenue in the specific optical tweezers and nano-optics.
Based on the post-earthquake investigation of the Beiling and Hanshen earthquakes, many welded rigid beam–column joints were found to exhibit brittle failure. The failure modes of the joint region and the overall steel frame structure under the action of the earthquake need to be studied. The seismic performance of different types of weakened beam-end interior joints was investigated. The finite element method was verified by high-strength steel beam–column joint tests conducted by our research team. Finite element modeling of weakened steel beam flanges and weakened steel beam web joints was carried out based on the validated finite element modeling method. The joints were studied and analyzed using seismic parameters such as joint stress clouds, equivalent story shear–inter-story displacement ratio curves, panel zone bending moment–shear ratio curves, ductility, stiffness, and energy dissipation. The results of this study showed that honeycomb open hole-type joints exhibit a better deformation and energy dissipation capacity compared to open circular web hole-type joints. However, their load carrying capacity is reduced, which is mainly due to the larger area of the web openings. Additionally, double reduced beam section (DRBS) joints exhibit superior seismic performance and plastic hinge outward movement characteristics compared to single reduced beam section (RBS) joints. It was also found that the deformation and energy dissipation of DRBS joints and steel beam honeycomb hole-type joints are mainly borne by the beams, with the panel zone’s participation in energy dissipation accounting for a smaller proportion of the energy.
Dirac degeneracy is a fourfold band crossing point in a three-dimensional momentum space, which possesses Fermi-arc-like surface states, and has extensive application prospects. In this work, we systematically study the exceptional effects of the robust chiral surface wave supported by photonic Dirac semimetal acts on the dielectric particles. Theoretical results show that orthogonal electromagnetic modes and helical or chiral whispering gallery modes (WGMs) of dielectric particles can be efficiently excited by the unidirectional spin-polarized surface wave. More importantly, optical forces exerted by the spin-polarized surface wave exhibit chirality-dependent symmetric behavior and high chiral Q factor with precise size selectivity. Our findings may provide potential applications in the area of chiral microcavity, spin optical devices, and optical manipulations.
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