Optical absorption tunability and local electric field distribution of gold-dielectric-silver three-layered cylindrical nanotube

The effects of inner nanowire radius, shell thickness, the dielectric functions of middle layer and surrounding medium on localized surface plasmon resonance (LSPR) of gold-dielectric-silver nanotube are studied based on the quasi-static approximation. Theoretical calculation results show that LSPR of gold-dielectric-silver nanotube and LSPR numbers can be well optimized by adjusting its geometrical parameters. The longer wavelength of $\left|\omega_{-}^{-}\right\rangle$ mode takes place a distinct red-shift with increasing the inner nanowire radius and the thickness of middle dielectric layer, while a blue-shift with increasing outer nanotube thickness. The physical mechanisms are explained based on the plasmon hybridization theory, induced charges and phase retardation. In addition, the effects of middle dielectric function and surrounding medium on LSPR, and the local electric field factor are also reported. Our study provides the potential applications of gold-dielectric-silver nanotube in biological tissues, sensor and related regions.     

Third order harmonics generation in multilayer nanoshells

Third order harmonics generation has been investigated for multilayer nanoshell structure. Numerical calculations show that the nonlinear susceptibility of this structure depends on the parameters such as size and kind of structure, relaxation time and pump photon energy. The intensity and position of third order nonlinear susceptibility peaks depend on shell thicknesses; smaller thicknesses have peak susceptibility at shorter wavelength.     

Scattering and absorption by spherical multilayer particles

We present a recursion formalism for the scattering coefficients of multilayered spherical particles which is more treatable for computer programs than the matrixformalism of Bhandari [1]. We computed explicitely the extinction and scattering cross section spectra of different metal coated spheres. Comparison with experimental results is done for gold-silver heterosystems. The spectra are in very good agreement with the experimental data.     

Electron-phonon interaction in spherical multilayer nanoheterostructures

The complete hamiltonian of an electron-phonon system in the second quantization representation for a complex spherical nanoheterostructure with an arbitrary number of semiconducting layers is obtained in a polarized continuum model for bounded volume and interface phonons. The energy of the electron ground state is calculated using the experimentally realized CdS/HgS/H₂O system as an example. The cause of the nonmonotonic dependence of the shift in the electron ground state on the HgS thickness is established as due to the interaction with bounded phonons. Fiz. Tverd. Tela (St. Petersburg) 39, 1109–1113 (June 1997)     

Photoacoustic cavitation in spherical and cylindrical absorbers

Photomechanical damage in absorbing regions or particles surrounded by a non-absorbing medium is investigated experimentally and theoretically. The damage mechanism is based on the generation of thermoelastic pressure by absorption of pulsed laser radiation under conditions of stress confinement. Principles of photoacoustic sound generation predict that the acoustic wave generated in a finite-size absorbing region must contain both compressive and tensile stresses. Time-resolved imaging experiments were performed to examine whether the tensile stress causes cavitation in absorbers of spherical or cylindrical shape. The samples were absorbing water droplets and gelatin cylinders suspended in oil. They were irradiated with 6-ns-long pulses from an optical parametric oscillator. Photoacoustic cavitation was observed near the center of the absorbers, even if the estimated temperature caused by absorption of the laser pulse did not exceed the boiling point. The experimental findings are supported by theoretical simulations that reveal strong tensile stress in the interior of the absorbers, near the center of symmetry. Tensile stress amplitudes depend on the shape of the absorber, the laser pulse duration, and the ratio of absorber size to optical absorption length. The photoacoustic damage mechanism has implications for the interaction of ns and sub-nslaser pulses with pigmented structures in biological tissue. Received: 9 October 1998 / Accepted: 5 January 1999 / Published online: 31 March 1999     

Optical properties of multilayer structures

The possibility of using the ellipsometry method for investigation of the optical properties of multilayer films and structures is shown. The optical properties of structures HfO₂/SiO₂/Si, HfO₂/Si, ZrO₂/Si, Ta₂O₅/Si, and Al₂O₃/Si are studied. It is found that a layer of hafnium silicate is formed at the interface between the HfO₂ film and Si. Annealing of the structures in oxygen shows that oxides studied are oxygen-permeable and that the thickness of SiO₂ at the film-substrate interface increases. The growth rate of SiO₂ layers depends on the chemical nature of an oxide. Al₂O₃ films are impermeable for oxygen diffusion. The production of layers of alloys (Al₂O₃) _x (HfO₂)_{1 ? x} is optimized, which allows one to obtain layers with a homogeneous distribution of elements over the thickness.     

Optical conductivity of multilayer graphene

The optical conductivity of graphene monolayer and multilayers are theoretically studied taking into account of the full dispersion, yielding results that are valid up to the ultraviolet region. Compared to the optical conductivity of monolayer graphene, extra peak structures appear in both the infrared and ultraviolet frequency regions for the multilayer case, which is understood as a combined effect of van Hove singularities in the energy band structures and optical transition selection rules. The number of ultraviolet peaks is equal to the number of layers. The number of infrared peaks in an even-layered graphene is equal to one half of the layer number. In odd-layered graphene, due to the existence of a monolayer-like subband, the number of infrared peaks is equal to that in the corresponding even-layered graphene with one layer less.     

Optical properties of multilayer structures

This paper describes the magneto-optical effects of metallic multilayers under the condition of total internal reflection. In the framework of the Green's dyadic technique, we present numerical simulations which account for the variation of the magneto-optical signal with the angle of incidence. The Attenuated Total Reflection (ATR) has become a new technique of characterization for thin films. We show, in this paper, optical effects due to a slight variation of the indice of refraction for thin dielectric films in reflection by the reflectivity and the Kerr rotation spectra of an optimized system. In transmission, this variation is brought to the fore by the near-field intensity spectra. Received 29 March 2000     

Natural oscillations of shielded multilayer spherical dielectric resonators

Characteristic equations and analytic expressions for the Q-factors are derived for a three-layer spherical dielectric resonator in a metal shield. The effect of dielectric coatings on the Q-factors of dielectric resonators is examined. The effect of a metal shield on thinning of the spectrum of a hollow spherical dielectric resonator is investigated.Kiev Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 35, No. 6/7, pp. 579–586, June–July, 1992.     

Gouy phase for full-aperture spherical and cylindrical waves

We investigate the Gouy phase shift for full-aperture waves converging to a focal point from all directions in two and three dimensions. We find a simple interpretation for the Gouy phase in this situation and show that it has a dramatic effect on reshaping sharply localized pulses.     

Optical properties of sliced multilayer gratings

Fabrication, calculation and optical properties of gratings fabricated by bevel cutting multilayer structures are discussed. Such gratings have very short period (about 100 nm) and provide high angular dispersion as compared to ruled, holographic or multilayer coated gratings without reduction of diffraction efficiency. Using graded multilayers it is possible to produce sliced multilayer gratings (SMG) with graded period (GSMG), which can focus radiation in one direction. Examples of SMG for various wavelengths in the interval 2–20 nm are considered.     

Converging spherical and cylindrical elastic–plastic waves of small amplitude

Converging spherical and cylindrical elastic–plastic waves in an isotropic work-hardening medium is investigated on the basis of a finite difference method. The small amplitude pressure is applied instantaneously and maintained on the outer surface of a spherical or a cylindrical medium. It is found that for undercritical loading, the induced wave structure is an elastic front followed in turn by an expanding plastic region and an expanding elastic region. For supercritical loading, the elastic front is followed in turn by an expanding plastic region, a narrowing elastic region and an expanding plastic region.After yielding is initiated, the strength of the elastic front is constant and equal to the critical loading pressure. The motion of the continuous elastic–plastic interface is discussed in detail. Spatial distributions of pressure near the axis show the strength of the converging wave is nearly doubled in the reflecting stage.     

Full tunability of laser femtosecond high-order harmonics in the ultraviolet spectral range

We demonstrate experimentally the full tunability of a coherent femtosecond source in the whole ultraviolet spectral region. The experiment relies on the technique of high-order harmonic generation driven by a near-infrared parametric laser source in krypton gas. By tuning the drive wavelength in the range between 1100 to 1900?nm, we generated intense harmonics from near to extreme ultraviolet. A number of photons per shot of the order of 10⁷ has been measured for the first harmonic orders. Many novel scientific prospects are expected to benefit from the use of such a table-top tunable source.     

Temperature and magnetic field tunability of composite metamaterials containing spherical semiconductor particles in far-infrared and terahertz regimes

The effect of temperature and dc magnetic field variations on effective electromagnetic parameters of metamaterials (MTMs) containing spherical semiconductor particles is studied theoretically. The effect of temperature is taken into account through its influence on semiconductor carrier density and mobility. The effect of dc magnetic field is included using an extension of the Mie theory, describing the interaction of a plane wave with a gyrotropic sphere. The effective parameters such as relative permittivity and permeability are calculated by proper application of the Maxwell Garnett (MG) theory and its extensions to quasi-static condition and multi-phase structures. Based on these theories, the temperature and dc magnetic field tunability of three different MTM structures is investigated. First a single phase medium is considered which contains spherical semiconductor particles of one kind, randomly dispersed in a dielectric host. Then two multi-phase structures containing (a) two kinds of spherical semiconductor particles or (b) spherical particles with core-shell topology are investigated. The two multi-phase MTM structures can exhibit negative index of refraction in far-infrared spectral region. The measure of the temperature and dc magnetic field tunability of effective parameters such as relative permittivity and refractive index of the structures is evaluated and it is shown specifically that the real part of refractive index can be tuned to get negative, zero or positive values in far-IR or THz regimes, but the imaginary part of the index and the Figure of Merit (FOM) are also quite sensitive to the temperature and magnetic field variations. The tunable MTMs can find new applications in THz devices such as switches, tunable mirrors, isolators, converters, polarizers, filters and phase shifters.     

Manipulated localized surface plasmon resonances in silver nanoshells coated with a spherical anisotropic layer

<正>The influences of the anisotropy of the outer spherically anisotropic(SA) layer on the far-field spectra and nearfield enhancements of the silver nanoshells are investigated by using a modified Mie scattering theory.It is found that with the increase of the anisotropic value of the SA layer,the dipole resonance wavelength of the silver nanoshell first increases and then decreases,while the local field factor(LFF) reduces.With the decrease of SA layer thickness, the dipole wavelength of the silver nanoshell shows a distinct blue-shift.When the SA layer becomes very thin,the modulations of the anisotropy of the SA layer on the plasmon resonance energy and the near-field enhancement are weakened.We further find that the smaller anisotropic value of the SA layer is helpful for obtaining the larger near-field enhancement in the Ag nanoshell.The geometric average of the dielectric components of the SA layer has a stronger effect on the plasmon resonance energy of the silver nanoshell than on the near-field enhancement.     

致冷多层干涉滤光片的光学特性

本文系统地研究了红外多层干涉滤光片的低温特性、并从薄膜的基本光学特性出发,推导了窄带滤光片、截止滤光片透射率与波长的温度效应.给出了截止滤光片截止波长的温度漂移公式.