Fano resonances in plasmonic core-shell particles and the Purcell effect

Despite a long history, light scattering by particles with size comparable with the light wavelength still unveils surprising optical phenomena, and many of them are related to the Fano effect. Originally described in the context of atomic physics, the Fano resonance in light scattering arises from the interference between a narrow subradiant mode and a spectrally broad radiation line. Here, we present an overview of Fano resonances in coated spherical scatterers within the framework of the Lorenz-Mie theory. We briefly introduce the concept of conventional and unconventional Fano resonances in light scattering. These resonances are associated with the interference between electromagnetic modes excited in the particle with different or the same multipole moment, respectively. In addition, we investigate the modification of the spontaneous-emission rate of an optical emitter at the presence of a plasmonic nanoshell. This modification of decay rate due to electromagnetic environment is referred to as the Purcell effect. We analytically show that the Purcell factor related to a dipole emitter oriented orthogonal or tangential to the spherical surface can exhibit Fano or Lorentzian line shapes in the near field, respectively.Comment: 28 pages, 10 figures; invited book chapter to appear in "Fano Resonances in Optics and Microwaves: Physics and Application", Springer Series in Optical Sciences (2018), edited by E. O. Kamenetskii, A. Sadreev, and A. Miroshnichenk

Magnetic dipole radiation tailored by substrates: numerical investigation

Nanoparticles of high refractive index materials can possess strong magnetic polarizabilities and give rise to artificial magnetism in the optical spectral range. While the response of individual dielectric or metal spherical particles can be described analytically via multipole decomposition in the Mie series, the influence of substrates, in many cases present in experimental observations, requires different approaches. Here, the comprehensive numerical studies of the influence of a substrate on the spectral response of high- index dielectric nanoparticles were performed. In particular, glass, perfect electric conductor, gold, and hyperbolic metamaterial substrates were investigated. Optical properties of nanoparticles were characterized via scattering cross-section spectra, electric field profiles, and induced electric and magnetic moments. The presence of substrates was shown to introduce significant impact on particle's magnetic resonances and resonant scattering cross-sections. Variation of substrate material provides an additional degree of freedom in tailoring properties of emission of magnetic multipoles, important in many applications.Comment: 10 page, 28 figure

Study on spontaneous emission in complex multilayered plasmonic system via surface integral equation approach with layered medium Green's function

A rigorous surface integral equation approach is proposed to study the spontaneous emission of a quantum emitter embedded in a multi-layered plasmonic structure with the presence of arbitrarily shaped metallic nanoscatterers. With the aid of the Fermi's golden rule, the spontaneous emission of the emitter can be calculated from the local density of states, which can be further expressed by the imaginary part of the dyadic Green's function of the whole electromagnetic system. To obtain this Green's function numerically, a surface integral equation is established taking into account the scattering from the metallic nanoscatterers. Particularly, the modeling of the planar multilayered structure is simplified by applying the layered medium Green's function to reduce the computational domain and hence the memory requirement. Regarding the evaluation of Sommerfeld integrals in the layered medium Green's function, the discrete complex image method is adopted to accelerate the evaluation process. This work offers an accurate and efficient simulation tool for analyzing complex multilayered plasmonic system, which is commonly encountered in the design of optical elements and devices. © 2012 Optical Society of America.published_or_final_versio

Enhanced surface plasmon resonance absorption in metal-dielectric-metal layered microspheres

We present a theoretical study of the dispersion relation of surface plasmon resonances of mesoscopic metal-dielectric-metal microspheres. By analyzing the solutions to Maxwell's equations, we obtain a simple geometric condition for which the system exhibits a band of surface plasmon modes whose resonant frequencies are weakly dependent on the multipole number. Using a modified Mie calculation, we find that a large number of modes belonging to this flat-dispersion band can be excited simultaneously by a plane wave, thus enhancing the absorption cross-section. We demonstrate that the enhanced absorption peak of the sphere is geometrically tunable over the entire visible range.Comment: 4 pages, 3 figures, Accepted for publication, Optics Letters. Revisions upon final revie

Field profiles for spherical conductive nanoparticles and metallic-shell/dielectric-core nano-composites

Profiles of the electric field strength |E|2/|E 0|2 for spherical metallic shells on a dielectric core are presented both inside the particle and outside. The dependence of the near-field strength and extent on shell thickness and total particle size is discussed qualitatively. Although the internal fields inside the shell and in the core are larger than for homogeneous particles, for not too thick shells, this does not translate into a stronger near-field away from the surface of the shell. The fields inside the shell, at the low energy resonance and close to it, are rotated by π/2 with respect to fields inside homogeneous particles, which means that the maximum field strengths in the shell are perpendicular to the incident polarisation. This follows from the fact that the low energy resonance for a shell is for the largest dipole moment of the whole system, which compensates the incident field. The largest moment is created when the same charges are collected at both interfaces (shell/medium and core/shell) along the incident polarisation. This creates regions of low field densities at the poles along the incident polarisation, because same charge fields repel each other. Following from that, the field lines are bunched up at the perpendicular poles, creating large field line densities and hence large fields at these points. The case for opposite charges across the interfaces creates the high energy, antisymmetric resonance