Change of the luminescence decay time for Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>: Eu nanocrystals embedded in synthetic opal

The opal-Lu_1.86Eu_0.14O₃ composites have been prepared using the developed technique for synthesizing luminophor nanocrystals in pores of synthetic opal through coprecipitation from a solution. It has been demonstrated that the position of the photonic stop band in the reflection spectrum of the infiltrated opal depends on the diameter of its spheres, the volume fraction of the embedded luminophor, and the angle of detection of the signal. The excitation and photoluminescence spectra of the composites have been analyzed, and the lifetime of the ⁵ D ₀ excited state of Eu³⁺ ions has been examined. It has been revealed that the luminescence decay time for the luminophor increases by almost one order of magnitude with an increase in its content in opal pores. This effect has been attributed to the change in the nanocrystal size and to the decrease in the contribution from the surface nonradiative recombination in luminophor nanolayers of the composites.     

An optical analog of the Borrmann effect in photonic crystals

Numerical simulation using the layered Korringa-Kohn-Rostoker (LKKR) method is applied to calculate the reflection and absorption spectra of an s-polarized electromagnetic wave incident on a faced-centered cubic photonic crystal (PC) with opal structure whose sites are occupied by two-layer metal-dielectric spheres. The reflection and absorption coefficients of the PC are analyzed as a function of the angle of incidence of the electromagnetic wave on the crystal surface. A range of wavelengths λ and angles of inclination θ to the normal is found in which the absorption experiences a sharp change under small variations of the above parameters. The appearance of peaks in the absorption spectrum of the PC is analyzed, and the spectrum is compared with the behavior of the reduced density of states. By the finite difference time domain (FDTD) method applied to the Maxwell equations, the spatial distribution of the energy density of electromagnetic field inside each of five layers of the PC is obtained at angles of incidence of 23° and 30° for a wave-length of 455 nm. It is demonstrated that the sharp maxima of the density of electromagnetic-field energy that are localized on the surfaces of absorbing metal spheres correspond to the absorption maximum. At the same time, at the absorption minimum, the maxima of the field energy density in each of the five layers are localized mainly between the lattice sites of the PC. An analogy between this phenomenon and the Borrmann effect, which is known in X-ray spectroscopy of ordinary crystals, is analyzed.     

Spectral properties of a one-dimensional photonic crystal with a resonant defect nanocomposite layer

The spectral properties of a one-dimensional photonic crystal with a defect nanocomposite layer that consists of metallic nanoballs distributed in a transparent matrix and is characterized by an effective resonance permittivity are studied. The problem of calculating the transmission, reflection, and absorption spectra of p-polarized waves in such structures is solved for oblique incidence of light, and the spectral manifestation of defect-mode splitting as a function of the volume fraction of nanoballs and the structural parameters is studied. The splitting is found to depend substantially on the nanoball concentration in the defect, the defect layer thickness, and the angle of incidence. The angle of incidence is found at which the resonance frequency of the nanocomposite is located near the edge of the bandgap or falls in the frequency region of a continuous spectrum. The resonance situation appearing in this case results in an additional transmission band or an additional bandgap in the transmission spectrum.     

Polarization-dependent suppression of Bragg reflections in light reflection from photonic crystals

This paper reports on an experimental and theoretical study of the spectra of Bragg reflection of light from opal-like photonic crystals near the critical angle of incidence ? _c , at which the Bragg reflection in the p polarization of reflected light disappears The objects studied were polymer photonic-crystal structures made up of polystyrene particles. It is shown that Bragg reflection for the electromagnetic TM mode becomes totally suppressed at an angle of incidence ? _c , which depends on the geometric parameters and dielectric constants of the spatially periodic structure.     

Control of absorption spectrum of a one-dimensional resonant photonic crystal

The crystal under consideration is a layered structure consisting of alternating layers of two materials, one of which is a resonantly absorbing gas. It is shown that the combination of the dispersion of an atomic gas with the dispersion of a photonic-bandgap structures allows one to efficiently control the transmission spectra of s- and p-polarized modes in these combined systems. It is found that the spectrum is highly sensitive to the position of the gas resonance frequency with respect to the bandgap edge and to a change in the gas pressure. The transmission, reflection, and absorption spectra of the resonant photonic crystal are studied at an angle of incidence equal to the Brewster angle of a seed photonic crystal. Possible applications of the found particular features of the dispersion of resonant photonic crystals are discussed.     

Two-dimensional light diffraction from thin opal films

This paper reports on experimental and theoretical investigations of light diffraction from thin films of synthetic opal. The diffraction patterns have been studied visually and recorded in different scattering geometries with the films illuminated with white unpolarized light. The diffraction pattern obtained with the film illuminated with a light beam along the [111] axis, which is normal to the film surface, has C ₆ symmetry and consists of six strong reflections arranged symmetrically with respect to the incident beam. This pattern becomes substantially more complicated when the film is illuminated by white light at an arbitrary angle to the [111] axis. An experimental study of the spectral response and angular relations of the diffraction patterns has established a fairly full pattern of transformation of diffraction reflections obtained under variation of the angle of light incidence on an opal film. The remarkably good matching of experimental and calculated data provides compelling evidence for light diffraction from thin opal films being two-dimensional.     

Spectral Ellipsometry of Multilayer ZnS/ZnSe Heterostructures

By the method of spectral ellipsometry with binary modulation of the polarization state the dispersions of the refractive index n, absorption coefficient k, and layer thickness in ZnS/ZnSe multilayer structures grown by the chemical gasphase deposition method from heteroorganic compounds on GaGaAssubstrates with ZnSe buffer layers have been determined. The efficiency of local ellipsometric measurements (with a light beam size less than 150 × 500 m) permitting mapping of the parameters of structures with A²B⁶ layers up to a few microns thick has been demonstrated. The optical properties of oxide layers formed on the zinc selenide surface have been investigated. Multilayer structures (ZnSe/ZnS) _n /ZnSe/GaAs with a pronounced exciton absorption and specific features in the reflection spectra coinciding in energy with exciton transitions, as well as Bragg mirrors with a reflection coefficient up to 99% in the blue region of the spectrum, have been studied.     

Anisotropy of light propagation in thin opal films

Thin opal films are prepared by crystallization in a moving meniscus, and their optical transmission spectra are recorded in polarized light and studied. It is shown that the anisotropy of light propagation in the films is unambiguously related to the photonic band structure of opal and depends on the angle of incidence, the orientation of the incidence plane with respect to the opal lattice, and the wavelength and polarization of the incident light. Azimuthal diagrams of transmitted polarized light are constructed in the range of photonic band gaps of three orders for oblique incidence of a light beam. The anisotropy is found to vary with the light wave-length independently in perpendicular polarizations. A model of the band structure of opal wherein opal is represented as an fcc lattice of close-packed spheres adequately describes the optical transmission of opal films only in the range of the first-order photonic band gap.     

One dimensional photonic band gap material as an omnidirectional reflector

In this article, the reflection properties in one-dimensional dielectric-dielectric photonic band gap (PBG) structure have been studied. We have used SiO₂ as material of low refractive index and Te as a high refractive index material. Reflectivity of proposed PBG structure is plotted as a function of wavelength and angle of incidence and omni-directional PBGs are computed theoretically. To obtain reflectance, we used transfer matrix method for solving Maxwell’s equations for electromagnetic wave in PBG structures. For a large range of frequency, the PBG structure is found to exhibit omni-directional reflection which can be exploited in devices such as optical resonators, mirrors, etc.     

Amplitude-phase reflectance spectra of amorphous silicon-based Bragg structures

Amplitude-phase spectra of light reflection from distributed Bragg reflectors and Fabry-Pérot microcavities based on a-Si: H/a-SiO_x: H thin films have been studied. The frequency dependence of the phase difference between the amplitude p-and s-light reflection coefficients within the photonic band gap is measured. The phase spectrum exhibits predominantly a monotonic, close-to-linear frequency behavior, except for spectral regions near the stop band edges and near the singularities related to the microcavity eigenmodes. The experimental spectra are compared with theoretical calculations based on the transfer matrix method and approximate analytical relations. A method based on analyzing amplitude-phase reflectance spectra is proposed for structural characterization of multilayer microcavity systems.     

Second harmonic generation in Ga nanoparticle monolayers

Ga nanoparticle monolayers formed by evaporation-condensation in ultrahigh vacuum and embedded in a transparent SiO_x matrix generate second harmonic (SH) signals in transmission and reflection when illuminated by a 150 fs, 800 nm laser pulses. The observed SH light exhibits a critical dependence on input and output polarizations, angle of incidence and azimuthal orientation of the samples. The results lead to a consistent picture of shape and orientation of the nanoparticles. Linear transmittance spectra in the visible range support these findings and the observed size dependence of the SH signal. Received 29 November 2000     

Inverse opal based on a polymer filler and transformation of its optical characteristics

Opal-like photonic crystals based on opal and inverse opal, which exhibit shifts of selective reflection bands toward both the long-wavelength and short-wavelength ranges with respect to the diffraction band of the initial opal consisting of SiO₂ spheres, have been grown. The contributions from the skeletons forming three-dimensional periodic structures and from the fillers to the spectral position of diffraction bands have been determined.     

Polarization stokes polarimetry of the amplitude and phase characteristics of surface plasmon polariton resonance

The amplitude and phase characteristics of internal reflection of gold nanofilms have been investigated using polarization modulation of electromagnetic radiation in the Kretschmann geometry. The component Q (the difference between the reflection coefficients R _s ² and R _p ² for the s and p polarizations, respectively) and the component V of the Stokes vector (the difference between the phases of the orthogonal components of linearly polarized radiation) of light reflected from a half-cylinder of the total internal reflection with gold films of different thicknesses on its flat surface have been measured as a function of the angle of incidence of light in the wavelength range 500–1000 nm. It has been demonstrated that, in the range of parameters corresponding to the manifestation of the plasmon polariton resonance (the angle of incidence of light, the wavelength, the metal film thickness), the dispersions of the amplitude and phase characteristics are in quantitative and qualitative agreement with the model concepts of a classical oscillator.     

Optical Characterization of Iridescent Wings of <Emphasis Type="Italic">Morpho</Emphasis> Butterflies using a High Accuracy Nonstandard Finite-Difference Time-Domain Algorithm

In certain species of moths and butterflies iridescent colors arise from subwavelength diffractive surface corrugation of the wing-scales. The optical properties of such structures depend strongly on wavelength, incidence angle, and state of polarization of illuminating radiation, and the viewing angle. In this paper, we study the reflection spectra of the wings of the Morpho didius butterfly by simulating a double-layered model of a transverse cross-section comprised of the ground scale and the cover scale. Each layer contains a certain quasi-periodic arrangement of tree-like subwavelength microstructures. The simulation is done using a high accuracy nonstandard finite-difference time-domain (FDTD) method in two dimensions. We assume that the structure is made of a slightly lossy dielectric material. The wavelength dependence of the complex refractive index for the ground scale of Morpho didius is assumed to be similar to that of Morpho sulkowskyi. The complex refractive index in the latter case was obtained by comparing the computed reflection/transmission spectra with corresponding experimental measurements at normal incidence.     

Synthesis of a periodic SiC/C nanostructure

Highly porous periodic structures consisting of a three-dimensional replica of pores in the initial opal lattice have been synthesized by high-temperature thermochemical treatment of opal matrices filled with carbon compounds, followed by dissolution of silicon dioxide. It has been shown that the main phases of the composite are carbon and silicon carbide. Based on the X-ray diffraction, Raman, and IR spectroscopy data, it has been assumed that the composite contains fragments of hexagonal diamond. The photoluminescence and optical reflection spectra of the composites have been measured.     

Magnetorefractive effect in nanocomposites: Dependence on the angle of incidence and on light polarization

The polarization and angular dependences of the magnetorefractive effect (MRE) in metal-insulator nanocomposites in reflection and transmission geometries have been calculated in terms of the high-frequency, spin-dependent tunneling mechanism. The MRE exhibits a weak polarization and angular response at small angles of incidence. The MRE in reflection and transmission starts to grow strongly with increasing angle of incidence. The MRE in reflection in nanocomposites with metal contents corresponding to the insulating phase near the percolation threshold reaches the largest values with p-polarized light at an angle of incidence close to the Brewster angle. The results of the calculation are in a qualitative agreement with experimental data.     

IR transmission and reflection spectra of structures with ZnTe and ZnTe/ZnMgTe quantum wires

The IR transmission and reflection spectra of ensembles of one-layer (ZnTe) and two-layer (ZnTe/ZnMgTe) quantum wires have been measured in s- and p-polarized light. The optical parameters of the structures and the material/vacuum volume ratio have been found by dispersion analysis. The frequencies of IR-active modes have been calculated using a quasi-electrostatic approximation and models of prolate ellipsoid and two-layer cylinders. The spectra of ensembles of ZnTe nanowires differ little from the spectrum of bulk ZnTe, exception for some softening of the LO-like mode. The spectra of two-layer ZnTe/ZnMgTe nanowires contain interface modes along with the TO-like mode. The calculated and measured data agree well.     

Spectroscopic and Structural Studies of Complex of [CU(DIEN)(CNGE)(ONO2)2] (Dien=Diethylenetriamine,CNGE=Cyanoguanid)

The electronic absorption spectrum (diffuse reflection spectrum) of the crystal of [Cu(dien)(cnge)(ONO₂)₂] has been measured. The experimental results are interpreted quantitatively with ligand field theory and the radial wave function of non-free copper (II), and our calculation values coincide well with the experimental results. As a result, the d-d absorption spectrum was explained satisfactorily. In particular, the structural characterizations whose degree of distortion of crystal structures of three Copper(II) complexes is different in this paper, are also discussed with their spectral behaviors. The experimental data provides significant correlation between the spectra and degree of distortion of coordination structures.     

Observation of Resonant Photon Tunneling in Photonic Double Barrier Structures

Reflectance and transmittance of 632.8 nm He-Ne laser light for photonic double barrier structures (consisting of a SF10 prism, SiO₂ layer, Al or Al₂O₃ active layer, SiO₂ layer and SF10 prism) were measured as a function of the angle of incidence for both the ρ- and s-polarized incidence. Sharp reflection dips and transmission peaks were observed at angles larger than the critical angle of total reflection. The appearance of the transmission peaks can be attributed to resonant photon tunneling through the photonic double barrier structures analogous to resonant electron tunneling through double potential barrier structures. Resonant tunneling is mediated by the long-range surface plasmon polariton in the case of the Al active layer and the electromagnetic guided modes in the case of the Al₂O₃ layer.This paper was originally presented at the seventh Meeting on Near Field Optics, which was held on July 1, 1998 at Nagoya University, Nagoya, organized by Research Group on Near Field Optics, the Optical Society of Japan, an affiliate of Japan Society of Applied Physics. The authors have won the Near Field Optics Award for their best presentation at the meeting.     

Extraordinary ray refraction in a large pitch helical medium

The phenomenon of extraordinary ray refraction in a helical liquid crystal with large (compared to the light wavelength) pitch has been studied by theoretical and experimental methods. At a sufficiently large angle of incidence relative to the pitch axis, the extraordinary ray exhibits reflection (reversal) from a certain layer of the medium. The ordinary ray, for which the system is optically isotropic, exhibits no such reflection. The experimental dependences of the transmitted and reflected (reversed) rays are described using the geometrical optics approximation taking into account the optical losses for scattering inside the liquid crystal.