Optical absorption of ultrafine metal spheres with dielectric cores

We compute the optical absorption of a glass containing a small fraction of silver particles with dielectric cores. The results are based on the Maxwell Garnett formalism. The dielectric permeability of the metallic shells is obtained by modifying experimental data for bulk silver to account for size dependent scattering of the conduction electrons. We find an absorption maximum in the visible range at a wavelength which, for sufficiently minute particles, depends rather strongly on the size of the cores and on their dielectric constant. The relevance of these results to recent experimental data by Smithard and by Genzel et al. is pointed out. We argue that their observed absorption maxima can be explained without invoking any quantum effects.     

Time evolution for infinitely many hard spheres

We construct the time evolution for infinitely many particles in F(x) = { *20c + ￥ 0 *20c |x| < a |x| \geqq a \Phi (x) = \left\{ {\begin{array}{*{20}c} { + \infty } \\ 0 \\ \end{array} } \right. \begin{array}{*{20}c} {|x|< a} \\ {|x| \geqq a} \\ \end{array}     

Raman scattering enhancement by dielectric spheres

Raman scattering experiments were performed on Si(60 nm)/metal/substrate structures with and without silica microspheres (with a diameter between 0.5 and 5 µm) on top. Raman scattering from the thin Si layer exhibits enhancements (~20) due to the dielectric spheres, where the enhancement factors depend on the diameter of the spheres. The interaction between light and dielectric spheres has been simulated by finite difference time domain calculations (FDTD), wherein particularly the electric energy density (ED) distribution in the thin Si layer was of concern. For microspheres with a diameter less than ~3 µm, the transverse ED distribution (perpendicular to the incident light direction) within the Si layer is characterised by a single peak centered on the optical axis. For larger diameters, a multimodal transverse ED distribution develops where the maximum is not centered on the optical axis. Using an ad‐hoc approach for surface enhanced Raman scattering in combination with the FDTD calculations, the experimental Raman observations are well accounted for. Copyright © 2013 John Wiley & Sons, Ltd.     

Metamaterials with dielectric and metallic inclusions in the cubic lattice

The method of integral equations, which is based on the Green function of periodically arranged sources, is used for analyzing periodic metamaterials (photonic crystals) in the form of the simplest metallic and dielectric inclusions into a rectangular cubic lattice in a dielectric medium (matrix). Dielectric inclusions in the form of parallelepipeds and cubes are considered, as well as similar metallic inclusions (perfectly conducting metal rods) and 1D nanosized structures with metallic layers. Metal inclusions are investigated in the case of ideal conduction and in the case of penetration of a field into the metal, which is simulated as an electron plasma. The results are applicable from microwave of optical frequencies.     

Two-dimensional metal inclusions in a dielectric crystal

Highly aggregated color centers in crystals of a wide-band-gap calcium fluoride insulator heated in a reducing atmosphere of vapors of calcium metal cation (“additive coloration” of crystals) have been studied using spectroscopy and atomic-force microscopy methods. These centers are large aggregates of anion vacancies and electrons, which transform into metal structures. The evolution of these structures with increasing number of such components has been traced from individual particles with two-dimensional structure to large film fragments. It has been shown that fragments are concentrated in isolated planes {111}, which are cleavage planes of the crystal with high contents of highly aggregated centers.     

含有密集随机分布内核的椭球粒子光散射特性研究

给出了一种结合射线追踪和蒙特卡罗方法计算含核粒子光散射的方法,内核粒子可以为稀疏分布也可为浓密分布.粒子外边界的反射和折射由射线追踪方法计算,而粒子内部的多次散射过程由蒙特卡罗方法模拟;当内核粒子为浓密随机分布时,其单次散射特性由基于静态结构因子（static structure factor）的浓密介质光散射理论计算.最后讨论了含核椭球粒子模型的单次散射特性. 关键词： 射线追踪技术 蒙特卡洛方法 光散射 椭球粒子     

Tuning of particle plasmon resonances in binary dielectric medium

Using light scattering spectroscopy, I demonstrate an approach to tune particle plasmon resonance in a binary dielectric media where silver nano-rods are embedded partially both in Anodic Aluminum Oxide (AAO) matrix and in air. A systematic experimental study under a controlled variation of the degree of embedding of nano-rods in AAO matrix has been presented. Experimental results have been interpreted based on the Drude model. Finite Difference Time Domain (FDTD) method has been employed to calculate the nature of the silver nano-rod resonance at the experimental conditions. Both the simulation results and theory corroborate the experimental findings.     

Characterization of dielectric spheres by spiral imaging

We study the spiral spectra scattered off transparent dielectric spheres when probed by different Laguerre-Gaussian light beams, carrying nested topological wavefront dislocations. We show that such scattering data may be employed to determine geometrical properties of the spheres, such as their position. The technique is a generalization of standard Mie scattering, and it can be extended to study and to characterize nanospheres.     

Surface lattice resonances in dielectric metasurfaees for enhanced light-matter interaction

Lithium niobate[LiNb03]is a versatile crystalline material for various photonic applications.With the recent advances in LiNb03-on-insulator[LNOI]thin film tech...     

Selective switching of individual multipole resonances in single dielectric nanoparticles

Following Mie theory, nanoparticles made of a high‐refractive‐index dielectric, such as silicon, exhibit a resonator‐like behavior and very rich resonance spectra. Which electric or magnetic particle mode is excited depends on the wavelength, the refractive‐index contrast relative to the environment, and the geometry of the nanoparticle itself. In addition, the spatial structure of the impinging light field plays a major role in the excitation of the nanoparticle resonances. Here, it is shown that, by tailoring the excitation field, individual multipole resonances can be selectively addressed while suppressing the excitation of other particle modes. This enables a detailed study of selected individual resonances without interference by the other modes.

     

Non compact single-layers of dielectric spheres electromagnetc behaviour

Single layer of dielectric spheres is a recognized model for the basic understanding of some aspects of photonic crystals. Here we present a systematic study of the effect of compacting in the electromagnetic transmission of dielectric spheres monolayers. Experiments were performed in the microwave domain (from 10 GHz to 30 GHz) with glass spheres of high dielectric permittivity ε = 7. Time Domain Finite Integration (TDFI) calculations were also accomplished. Experimental data and TDFI calculations agreement provides a double check on the lack of experimental artefacts and the correctness of simulation settings. Following the evolution of the lower frequency spectral peak with layer compacting ratio, we established three different electromagnetic regimes. For the higher and lower compacting ratio regimes, the peak frequency matches isolated sphere pure resonances, while for intermediate values of compacting, some transition between these two modes takes place. Extending the study to the complete frequency range, we find that sphere single layers transmission spectra become closer to isolated sphere scattering calculations as the compacting ratio is decreased. However as the agreement remains imperfect even for our lowest compacting measurable layer, we conclude that some structure contribution cannot be neglected even for low compact layers.     

Fluctuations of dielectric constant in a system of hard spheres

The correlation function for fluctuations of a dielectric constant in a latex-like suspension of spherical particles was calculated. An exact analytical expression was derived for the correlation function using the Percus-Yewick approximation for a system of hard spheres. The obtained results made it possible to calculate the indicatrix of single scattering, the extinction coefficient, and the transport mean path. It is shown that, starting with a volume content of about ten percent, the “gas” approximation becomes invalid, and optical parameters begin to depend on concentration in quite a complicated manner. In particular, the extinction length and the mean transport path, which are the basic parameters in describing the coherent effects in multiple scattering, vary nonmonotonically with concentration. It is found that there exists a range of sizes and concentrations of scattering particles in which an effect similar to the emergence of blue phase in liquid crystals can be observed.     

Resonant behavior of dielectric objects (electrostatic resonances)

Resonant behavior of dielectric objects occurs at certain frequencies for which the object permittivity is negative and the free-space wavelength is large in comparison with the object dimensions. Unique physical features of these resonances are studied and a novel technique for the calculation of resonance values of permittivity, and hence resonance frequencies, is proposed. Scale invariance of resonance frequencies, unusually strong orthogonality properties of resonance modes, and a two-dimensional phenomenon of "twin" spectra are reported. The paper concludes with brief discussions of optical controllability of these resonances in semiconductor nanoparticles and a plausible, electrostatic resonance based, mechanism for nucleation and formation of ball lightning.     

Optical resonances in one-dimensional dielectric nanorod arrays: field-induced fluorescence enhancement

Arrays of transparent dielectric nanorods are shown to produce very large local field enhancements at specific resonant conditions. These structures would lead to enhancement of molecular fluorescence signals without quenching. The resonant angular width and field enhancements are analytically derived as a function of wavelength, grating period, rod radius, and dielectric constant.     

Effective dielectric constant of dilute polydisperse suspensions of spheres

We study the effective dielectric constant of a dilute, polydisperse suspension of spheres embedded in a uniform background. We consider a frequency region where the dipole polarizability of individual spheres exhibits a resonance. We evaluate the effective dielectric constant to second order in the volume fraction employing the dipole approximation, which in previous work has been shown to be applicable in resonance. We apply our results to suspensions of spheres with identical and uniform dielectric constant, assuming a log-normal distribution of sphere radii.     

Tunable terahertz metamaterial based on resonant dielectric inclusions with disturbed Mie resonance

Tunable metamaterial operating in terahertz (THz) frequency range based on dielectric cubic particles with deposited conducting resonant strip was investigated. The frequency of the first magnetic type Mie resonance depends on the electric length of the strip. It can be changed under photoexcitation or applied voltage. This method of control was used for a design of tunable double negative metamaterial based on dielectric resonant inclusions and wire medium.     

Optical characteristics of a cluster of closely-packed dielectric spheres

We employ the pseudospectral time-domain technique to simulate light scattering by a cluster of mono-disperse dielectric spheres. The total scattering cross-section (TSCS) spectrum of the cluster is obtained and analyzed. Research findings show that the TSCS spectrum exhibits characteristics of the cluster geometry as a whole, as well as characteristics of the constituent dielectric spheres. Furthermore, an optical signature indicative of the constituent sphere size is identified, suggesting the possibility to obtain microscopic geometrical information of a closely-packed geometry from multiply scattered light.