Spherical Dielectric Particles Research Articles

Broadband Radiation of Small Dielectric Particles

A qualitatively new theoretical model of broadband (“white”) thermal radiation of small dielectric particles is proposed. The hypothesis that the high intensity of this radiation can be caused not by extremely high temperature but dielectric properties of the material and/or size effect is stated and justified. The radiation intensity of an absolutely black body and a spherical dielectric particle are calculated depending on the photon gas dimension.

Mie scattering revisited: Study of bichromatic Mie scattering of electromagnetic waves by a distribution of spherical particles.

Two experiments to measure the size of microscopic dielectric spherical particles immersed in purified water with spheres of a nominal diameter 5.2 ± 0.15 μm have been carried out in order to revisit Mie scattering techniques. The first experiment uses a 1 mW helium-neon (He-Ne) laser with a wavelength of 632.8 nm, while the second one is carried out using a diode laser of 780.0 nm wavelength and a nominal power of 80 mW. The distribution of the scattered light intensity is recorded experimentally, and since the theoretical background has been known for several decades (see references), only a modest amount of theory is included. We considered the Mie scattering by a set of spheres of different diameters in our case with a distribution of sphere diameters with mean diameter 5.2 μm and standard deviation 0.15 μm. Our measured Mie scattering angular distribution accounts for the effect of the diameter distribution, which we assume to be a Gaussian distribution. Our results indicate that there is very good agreement between experiment and theoretical predictions. The technique we offer here is found to be useful to familiarize technicians who work in the areas of applied optics, such as chemistry, electronics, water contamination, and optical instruments with Mie scattering techniques, and who may not have a formal introduction to the electromagnetic theory. One specific area in which these techniques might be useful is the study of aerosols that may arise when naturally produced droplets from humans, such as those produced by coughing, sneezing, talking, and breathing, are present, as it happens in response to the Severe Acute Respiratory Syndrome Coronavirus 2, also known as SARS-CoV-2.

Orbital Angular Momentum Tuning Using a Phase Only Parallel Aligned LCoS Display

We propose two schemes for achieving continuous and complete orbital angular momentum tuning using a simple device based on a phase only parallel aligned liquid crystal on silicon (PA-LCoS) display, where the tuning is done by combining two beams with opposite orbital angular momentum (OAM) and orthogonal polarization, whose relative weight is controlled by changing the input beam state of polarization (SoP). We use an optical tweezers toolbox to simulate the optical force field of the tuned beams applied to dielectric spherical particles in order to prove the applicability of the method.

Широкополосное излучение малых диэлектрических частиц

A qualitatively new theoretical model of broadband ("white") thermal radiation of small dielectric particles is proposed. It is suggested and justified that the high intensity of this radiation may be due not to an extremely high temperature, but to the dielectric properties of the material and/or the dimensional effect of thermal radiation. The calculation of the radiation intensity of a blackbody and a spherical dielectric particle depending on the photon gas dimension is performed.

Light Pressure on an Inhomogeneous Spherical Particle in the Field of Laser Tweezers

The light pressure on an inhomogeneous spherical dielectric particle consisting of a shell and a core with different refractive indices is considered. The forces acting on this particle in a laser beam with a Gaussian intensity profile have been found in the geometrical optics approximation. The radiation propagation is analyzed by taking into account the different refractive indices of the core, the shell, and the medium surrounding the particle. The light pressure is shown to depend significantly on the core radius, which allows the core size to be estimated from the spatial dynamics of the particle in the field of optical tweezers.

Hybrid rectennas of printed dipole type on Double Negative Dielectric Media for powering sensors via RF ambient energy harvesting

The harvesting of ambient RF power would be a promising respond to the requirement of continuous power support the sensors of wireless networks, without using batteries. The devices used for scavenging the RF power are known by the term rectennas and their first unit is an antenna which captures the power of impinging RF signals and then guide it to be rectified and stored by the rest of rectennas' grades. This article proposes an antenna scheme suitable for rectenna applications at the Universal Mobile Telecommunication System (UMTS), from 1.92 GHz to 2.17 GHz. The antenna is composed of planar dipoles with specific layout, printed on dielectric substrate with Double Negative (DNG) electromagnetic properties. The DNG substrate is composed of dielectric spherical particles that are hosted in a medium of very low dielectric constant and have suitable size in order to resonate at the UMTS band, thus developing high intensity electromagnetic fields. The dipoles embedded to this hybrid structure gather amounts of RF power larger than in case of an ordinary dielectric. Moreover, the antenna was synthesized with intend a matching network between it and the rectifier not to be used, thus avoiding potential losses and complexity. Considering that the rectenna will work in mobile telecommunication environment, where the incoming signals are of statistical nature, its performance was studied using its Mean Effective Gain (MEG), the Cross Polarization Power Ratio (XPR) and the Directions of Arrival (DoAs) of the incoming waves. Statistical mean values for DC voltages and power equal to 172 mV and 65 μW respectively and with mean efficiency 58% were obtained for incident power 0.2 mW, while, depending on case, the DC voltage may exceed the 300 mV and the power the 160 μW.

Core-shell particles as efficient broadband absorbers in infrared optical range.

We demonstrate that efficient broadband absorption of infrared radiation can be obtained with deeply subwavelength spherical dielectric particles covered by a thin metal layer. Considerations based on Mie theory and the quasi-static approximation reveala wide range of configuration parameters, within which the absorption cross section reaches the geometrical one and exceeds more than by order of magnitude the scattering cross section in the infrared spectrum. We show that the absorption is not only efficient but also broadband with the spectral width being close to the resonant wavelength corresponding to the maximum of the absorption cross section. We obtain a simple analytical expression for the absorption resonance that allows one to quickly identify the configuration parameters ensuring strong infrared absorption in a given spectral range. Relation between the absorption resonance and excitation of the short-range surface palsmon modes in the metal shell of particles is demonstrated and discussed. Our results can be used as practical guidelines for realization of efficient broadband infrared absorbers of subwavelength sizes desirable in diverse applications.

The Influences of Optical Forces on the Lattice Structure of Electrorheological Suspensions

In order to investigate the influences of the optical forces on the lattice structure of an electrorheological (ER) suspension, on the basis of the experiment of Michael M. Burns etal., comparing their sample with an Electrorheological suspension, this paper substantially discusses the influences of intense light beams on the interaction between the dielectric particles immersed in electrorheological suspensions (ER). It respectively calculates out the optical forces exerted either on the polystyrene spheres in the sample of Michael M. Burns etal. Or on the corn-starch spheres in an ER suspension, the calculation results of this paper show that increasing the intensities of the incident laser beams or the gradient of the applied electric field can generate stronger optical forces acting on the spherical dielectric particles in an ER fluid than acting on those spheres with nearly the same mass and figuration in the suspension sample of Michael M. Burns etal.. Similar to the experimental result of Michael M. Burns et al., when increasing the intensities of the incident laser beams or the gradient of the electric field up to a critical value, it will give rise to the optical crystallization and optical binding of ER suspensions.

Dielectric Spherical Particle on an Interface in an Applied Electric Field

Here we study the force due to an applied electric field on a spherical particle trapped at a planar interface. Electric fields applied in either a normal or tangential direction to the interface a...

Revolution and spin of a particle induced by an orbital-angular-momentum-carrying Laguerre-Gaussian beam in a dielectric chiral medium

We reveal an interesting phenomenon of the acceleration and deceleration of the phase rotation for an orbital-angular-momentum-carrying Laguerre-Gaussian beam in a chiral medium. Under this circumstance, the differences between the optical force and optical torque exerted on a dielectric spherical particle for chiral and achiral cases are demonstrated. The optical force and torque are exerted on the particle simultaneously, which makes the particle revolve and spin simultaneously, as a planet in the solar system. We hope the results may point to a unique routine of optical manipulation.

Periodical focusing mode achieved through a chain of mesoscale dielectric particles with a refractive index near unity

Abstract At present three main mechanisms of optical propagation with periodically focused modes in the chains of dielectric spherical particles with a refractive index near n = 1.59 are considered in the literature: evanescent whispering gallery mode coupling, photonic nanojet-induced modes, and the propagation of transverse magnetic modes under conditions close to Brewster angle geometry. In this paper we show that quasi-periodical focusing modes exist in a range of near unity refractive indices for chains of dielectric particles in both spherical and cubic forms. We also show that such a medium can be considered a gradient index waveguide with a parabolic law of refractive index variation.

Sum-Frequency Generation from a Thin Spherical Layer: I. Analytical Solution

We have analyzed the influence of the angle between the wave vectors of two incident waves (the opening angle) and of the type of the anisotropy of a nonlinear layer on the shape of the directivity pattern of a sum-frequency harmonic generated by the two plane elliptically polarized electromagnetic waves from a thin spherical optically nonlinear layer deposited on the surface of a dielectric spherical particle placed in a dielectric. Our analysis has shown that, if the radius of the thin spherical nonlinear layer is small, the shape of the directivity pattern will change significantly with increasing opening angle only for some types of anisotropy: the main lobes shift toward the direction that is opposite to the direction of the sum of the wave vectors of the incident waves. For three types of anisotropy, the directivity patterns have similar shapes. We have also found that, for one of the types of the anisotropy, the shape of the directivity pattern remains unchanged upon a change in the opening angle. The mathematical properties of functions describing the spatial distribution of the generated harmonic have been determined. In particular, it has been found that, upon incidence of linearly polarized waves on a thin nonlinear spherical layer that possesses either solely chiral or solely nonchiral nonlinear properties, linearly polarized radiation of the sum-frequency harmonic is generated.

Dielectric magnetic microparticles as photomagnonic cavities: Enhancing the modulation of near-infrared light by spin waves

The coupling between spin waves and optical Mie resonances inside a dielectric magnetic spherical particle, which acts simultaneously as a photonic and magnonic (photomagnonic) cavity, is investigated by means of numerical calculations accurate to arbitrary order in the magnetooptical coupling coefficient. Isolated dielectric magnetic particles with diameters of just a few microns support high-$Q$ optical Mie resonances at near-infrared frequencies and localized spin waves, providing an ultrasmall and compact platform in the emerging field of cavity optomagnonics. Our results predict the occurrence of strong interaction effects, beyond the linear-response approximation, which lead to enhanced modulation of near-infrared light by spin waves through multimagnon absorption and emission mechanisms.

Spherical and cylindrical particle resonator as a cloak system

The concept of dielectric spherical or cylindrical particle in resonant mode as a cloak system is offered. In fundamental modes (modes with the smallest volume correspond to |m| = l, and s = 1) the field is concentrated mostly in the equatorial plane and at the surface of the sphere. Thus under resonance modes, such perturbation due to cuboid particle inserted in the spherical or cylindrical particle has almost no effect on the field forming resonance regardless of the value of internal particle material (defect) as long as this material does not cover the region where resonance takes place.

Negative refraction in metamaterials based on dielectric spherical particles

Negative refraction (NR) metamaterials are featured with unique physical properties and potential to realize full control of electromagnetic waves, which have attracted much attention since the last decade. However, few researches focus on the realization of three-dimensional dielectric NR metamaterials in optic frequency, and the current design methods need further development. In this paper, a three-dimensional all-dielectric NR metamaterial with two NR bands has been realized based on proper excitation of electric and magnetic multipoles. It is also predicted that the coupling of magnetic dipole and electric dipole can lead to the NR bands in near-infrared frequencies, and NR in the visible frequencies can be achieved by the coupling of magnetic quadrupole and electric dipole. Band structures and equal-frequency surfaces of proposed metamaterial arranged in the periodic cubic lattice are solved by adopting the plane wave expansion method, and then the results verify the existence of these two NR frequency bands in periodic metamaterials. In this way, the characteristic parameters such as transmission and absorption of light in two NR bands are also analyzed. In the meantime, the finite-deference time-domain method is used to intuitively display the phenomenon of NR and investigate the effects of disorder in particle arrangement. Besides, it is found that the proposed metamaterials have fine robustness to the disorder in particle arrangement, and these two NR bands can be tuned by adjusting volume fraction. In brief, this work provides means for preliminary designing, profound analysis and intuitively exhibition of NR metamaterials based on dielectric particles.

Time-dependent electrophoresis of a dielectric spherical particle embedded in Brinkman medium

An expression for electrophoretic apparent velocity slip in the time-dependent flow of an electrolyte solution saturated in a charged porous medium within an electric double layer adjacent to a dielectric plate under the influence of a tangential uniform electric field is derived. The velocity slip is used as a boundary condition to solve the electrophoretic motion of an impermeable dielectric spherical particle embedded in an electrolyte solution saturated in porous medium under the unsteady Darcy–Brinkman model. Throughout the system, a uniform electric field is applied and maintains with constant strength. Two cases are considered, when the electric double layer enclosing the particle is thin, but finite and when of a particle with a thick double layer. Expressions for the electrophoretic mobility of the particle as functions of the relevant parameters are found. Our results indicate that the time scale for the growth of mobility is significant and small for high permeability. Generally, the effect of the relaxation time for starting electrophoresis is negligible, irrespective of the thickness of the double layer and permeability of the medium. The effects of the elapsed time, permeability, mass density and Debye length parameters on the fluid velocity, the electrophoretic mobility and the acceleration are shown graphically.

One stone, two birds: silica nanospheres significantly increase photocatalytic activity and colloidal stability of photocatalysts

Silver-doped silver chloride [AgCl(Ag)] nanoparticles represent a unique class of visible-light-driven photocatalysts, in which the silver dopants introduce electron-abundant mid-gap energy levels to lower the bandgap of AgCl. However, free-standing AgCl(Ag) nanoparticles, particularly those with small sizes and large surface areas, exhibit low colloidal stability and low compositional stability upon exposure to light irradiation, leading to easy aggregation and conversion to metallic silver and thus a loss of photocatalytic activity. These problems could be eliminated by attaching the small AgCl(Ag) nanoparticles to the surfaces of spherical dielectric silica particles with submicrometer sizes. The high optical transparency in the visible spectral region (400–800 nm), colloidal stability, and chemical/electronic inertness displayed by the silica spheres make them ideal for supporting photocatalysts and significantly improving their stability. The spherical morphology of the dielectric silica particles can support light scattering resonances to generate significantly enhanced electric fields near the silica particle surfaces, on which the optical absorption cross-section of the AgCl(Ag) nanoparticles is dramatically increased to promote their photocatalytic activity. The hybrid silica/AgCl(Ag) structures exhibit superior photocatalytic activity and stability, suitable for supporting photocatalysis sustainably; for instance, their efficiency in the photocatalytic decomposition of methylene blue decreases by only ∼9% even after ten cycles of operation.

Scattering of Lommel beams by homogenous spherical particle in generalized Lorenz–Mie theory

In this paper, we investigate the generalized Lorenz–Mie theory (GLMT) for calculating the scattered field components of Lommel beams by a homogenous spherical particle. We use also, the integral localized approximation for computing the beams shape coefficients for this kind of beams. These coefficients are of great interest in the description of beams in the GLMT but valuable only if the axicon angle is small enough. This work is devoted to the study the far field scattered intensity by homogenous dielectric spherical particle illuminated by x-linearly Lommel beams. All through this work, the effects of various parameters characterizing the feature of Lommel beams on the scattered intensity are analysed numerically.

Theoretical estimation of nonlinear optical force on dielectric spherical particles of arbitrary size under femtosecond pulsed excitation

Experimental evidence indicates that high-repetition-rate ultrafast pulsed excitation is more efficient in optical trapping of dielectric nanoparticles as compared with continuous-wave excitation at the same average power. The physics behind the different nature of force under these two excitation conditions remained deceptive until quite recently when it was theoretically explained, in the dipole limit, as a combined effect of (1) repetitive instantaneous momentum transfer and (2) optical Kerr nonlinearity. The role of optical Kerr effect was theoretically studied for larger dielectric spherical particles, in the ray optics limit, also. However, a theoretical underpinning is yet to be established as to whether the effect of optical nonlinearity is omnipresent across different particle sizes, which we investigate here. Using localized approximation of generalized Lorenz-Mie theory, we theoretically analyze the nature of force (and potential) and provide a detailed comparative discussion between this generalized scattering formulation with dipole scattering formulation for dielectric nanoparticles.

Dynamic magnetic losses in powders consisting of metallized dielectric particles at microwaves

In this study the interaction of microwaves with dielectric spherical particles covered by conductive shell was modelled. Dependencies of effective permittivity and permeability of powders, consisting of core-shell metallized dielectric particles, on frequency, radius and permittivity of core, as well as thickness and conductivity of metallic shell were obtained. The present paper introduces a novel technique for calculation of effective permittivity and permeability based on results of direct finite element method simulations of electromagnetic fields within the model. Equations for calculation of effective electrodynamics parameters were derived from a combination of surface impedance equations and impedance values for an ideal conductor and an ideal magnetic mirror.The contribution of electric and magnetic losses was evaluated and compared for completely conductive particles and dielectric particles with a conductive shell. It was identified that for completely conductive particles and for metallized dielectric particles the imaginary part of effective permeability is orders of magnitude greater than the imaginary part of effective permittivity. In addition, the imaginary part of effective permeability of core-shell metallized dielectric particles can be nearly twice as greater than the one of completely conductive particles. Moreover, the maximum of dynamic magnetic losses is reached when the conductive shell thickness is less than skin depth. Therefore, we can conclude that dynamic magnetic losses is the main mechanism of microwave heating of such particles.