On optical properties of nonspherical inhomogeneous particles

To solve the problem of light scattering by multilayer scatterers of an arbitrary axisymmetric shape, a separation of variables method that involves special scalar potentials and their expansions in spherical functions is developed. The approach is shown to yield highly exact results even for particles that have 100 layers or more. A graphic library that illustrates the optical properties of layered and homogeneous (with an effective refractive index) spheroids, spheres, and Chebyshev particles of various shapes and sizes (about 650 figures) is created and is put on the Internet. It is noted that the linear polarization of radiation transmitted forward through a polydisperse medium containing partially oriented nonspherical porous particles strongly depends on the structure of scatterers. It is shown that the difference between the degrees of polarization of layered and corresponding homogeneous scatterers can exceed 200–300%.     

Bounds and exact theories for the transport properties of inhomogeneous media

We investigate the bounds of Milton on the transport coefficient of a two-component composite, in their application to the square and hexagonal arrays of cylinders, and the three cubic lattices of spheres. We show that, in all five cases, as more information is supplied about the geometry of the composite, the bounds converge to the precise point obtained from an exact theory specific to the geometry in question. We illustrate the use of the bounds in determining whether a set of known values of the transport coefficient adequately specifies the general behaviour of that quantity. We determine the values of two structure-dependent parameters for cell materials with spheroidal cells and the value of one parameter for hexagonal and square arrays of cylinders with missing array elements. These parameters determine bounds both on the transport and on the elastic properties of the respective materials.     

Experimental and theoretical studies of polaron optical properties in KNbO3 perovskite

Time-resolved absorption and luminescence spectra have been measured in KNbO₃ perovskite crystals after pulsed band-gap excitation by 200 fs laser pulses and 10 ns electron pulses. Quantum chemical calculations using the large unit cell periodic model support the interpretation of the observed transient absorption bands at 0.8 and 1.1 eV as the self-trapped electron polarons and bound hole polarons, respectively. The activation energy for the 2.2 eV green luminescence quenching is 0.05 eV. We suggest that the short lifetime (<15 ns) of the luminescence at RT is caused by the radiative recombination of nearest electron and hole polarons.     

Low-energy peculiarities of the optical properties of inhomogeneous alloys

The optical properties of PdMn_0.7Fe_0.3, Pd₂AuFe and GdCu alloys of different homogeneity have been investigated. Possible reasons for the peculiarities typical of all alloys studied (deviation from the Drude behavior and low-energy absorption of light at ?ω < 0.5 eV) are discussed. Occurrence of these anomalies is related to general features of studied objects microstructure (phase inhomogeneity of medium in the form of presence in high-resistivity matrix of alloys of small inclusions of metal type.     

Experimental and theoretical study of the multiple scattering of acoustical waves in inhomogeneous media

To describe the propagation of acoustic waves in concrete, we used the results of Waterman for the complex propagation constant in a scattering medium. This makes it possible to calculate the attenuation and phase velocity in the medium concerned. The agreement between theoretical and experimental results being very poor for concrete, we searched for a synthetic medium with a closer correspondence to the theoretical pattern assumed, to determine whether the theory works better for such media. In fact, the synthetic medium gave experimental results in good agreement with the theoretical ones. The results allow us to suggest the use of a more precise treatment suggested by Fikioris and Waterman, which could lead to a better agreement for concrete. However, this extension will be reserved for a later publication.To put an end to the confusion created by misprints in the expressions of certain publications, which have been used as such without correction by some authors, we include here full details of the theory used by us, and give an explanation of our notation.     

Effect of phosphorus on the electronic and optical properties of naphthoxaphospholes: theoretical investigation

Density functional theory (DFT) and time-dependent DFT calculations were performed to elucidate the electronic and optical properties of 2-R-naphthol[2,3-d]oxaphospholes (R-NOPs). On the basis of the calculated results, the poor π overlap between the 3p_z orbital of P atom and the 2p_z orbitals of other atoms and increasing polarity of P atom result in a reduced energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital. When these two effects are considered simultaneously, the absorption energies obtained for the S₁ state can be below 3.00 eV according to replace the P atom of oxaphosphole ring by As atom (increasing the poor π overlap) and change the functional groups (increasing polarity). The origin of these two effects is the inherent size of the 3p orbital of P atom. The role of P atom in the control of the electronic and optical properties of R-NOPs is clearly elucidated.     

Experimental and theoretical investigations of optical properties of GaN/AlGaN MQW nanostructures. Impact of built-in polarization fields

We report the results from detailed optical spectroscopy from MOCVD grown GaN/AlGaN multiple quantum wells (MQWs), as opposed to most previous studies where MBE was employed by means of photoluminescence (PL) technique. In this paper we will present theoretical and experimental results demonstrating how polarization induced electric fields and bound interface charges in GaN/AlGaN MQWs affect the emission peak energy, PL line shape, as well as the emission line width. Theoretically estimated fields in this work are consistent with experimental data. Transition energy of the heavy hole and electron ground state Ee-hh in GaN/AlGaN MQWs were calculated and it is found that it stays in good agreement with the experimental data.     

Experimental and theoretical studies on high-temperature thermal properties of fibrous insulation

In the present paper, an experimental apparatus has been developed to measure heat transfer through high-alumina fibrous insulation for thermal protection system. Effective thermal conductivities of the fibrous insulation were measured over a wide range of temperature (300-973 K) and pressure (10⁻²-10⁵ Pa) using the developed apparatus. The specific heat and the transmittance spectra in the wavelength range of 2.5-25 μm were also measured. The spectral extinction coefficients and Rosseland mean extinction coefficients were obtained from transmittance data at various temperatures to investigate the radiative heat transfer in fibrous insulation. A one-dimensional finite volume numerical model combined radiation and conduction heat transfer was developed to predict the behavior of the effective thermal conductivity of the fibrous insulation at various temperatures and pressures. The two-flux approximation was used to model the radiation heat transfer through the insulation. The experimentally measured specific heat and Rosseland mean extinction coefficients were used in the numerical heat transfer model to calculate the effective thermal conductivity. The average deviation between the numerical results for different values of albedo of scattering and the experimental results was investigated. The numerical results for ω=1 and experimental data were compared. It was found that the calculated values corresponded with the experimental values within an average of 13.5 percent. Numerical results were consistent with experimental results through the environmental conditions under examination.     

Surface-induced optical anisotropy of inhomogeneous media

We demonstrate that the presence of interfaces induces anisotropy in the optical properties of thin inhomogeneous layers. Several mechanisms are discussed that can control the properties of this surface-induced anisotropy. We found that the effective refractive indices for s- and p-polarized fields are different and depend on the thickness of the layer, concentration and optical properties of inclusions in the layer, and the angle of incidence.     

Low-frequency optical conductivity of inhomogeneous alloys

The optical conductivity of PdMn_0.7Fe_0.3, Pd₂AuFe, and GdCu alloys with different degrees of homogeneity has been measured. Possible reasons for a low-frequency (E < 1 eV) anomalous maximum in the σ(ω) curves are discussed. The deviation from the Drude behavior of σ(ω) is assigned to the presence of small “metallic” inclusions in the high-resistivity matrix of these alloys.     

Synthesis,structural aspects and nonlinear optical properties of novel phthalimide derivatives: theoretical and experimental approach

Novel phthalimides ( 1 , 2 , 3 ) possessing variability of cyclic amines have been synthesized and characterized by analytical and spectroscopic techniques. Phthalimide 1 and 2 crystallized in a triclinic system with space group Pī; however, an orthorhombic system with a chiral space group of P2₁2₁2₁ was observed for 3 possessing piperidine cyclic amine. The hydrogen atoms attached to the central chiral carbon were oriented anti to each other resulting in minimum steric repulsion. The occurrence of C–H···O hydrogen bonds in 1 , 2 , 3 enabled the building of several supramolecular structures. Hyperpolarizability 197.6096 Debye Ų calculated for 1 was found to be higher than the hyperpolarizabilities, 138.0836 and 165.2521 Debye Ų measured for 2 and 3 , respectively. Subsequently, phthalimides ( 1 , 2 , 3 ) were assessed for second harmonic generation (SHG) response, and a negligible response was recorded for 1 and 2 ; however, 3 showed a significant response of 14.2 mV. In addition to acentric structure, helical structural motifs identified in 3 could be responsible for its enhanced SHG response. Copyright © 2014 John Wiley & Sons, Ltd.     

40 Gb/s all-optical logic NOR and OR gates using a semiconductor optical amplifier: Experimental demonstration and theoretical analysis

We experimentally and theoretically demonstrate 40 Gb/s all-optical logic NOR and OR gates based on a semiconductor optical amplifier (SOA) and a blue shifted optical bandpass filter (OBF). Two kinds of data formats are discussed, namely return-to-zero (RZ) format and nonreturn-to-zero (NRZ) format. The logic NOR and OR functions of RZ format are realized at the OBF detuning of −0.22 nm and −0.44 nm, respectively. The logic NOR function of NRZ format is realized at the OBF detuning of −0.24 nm. The simulation is in good agreement with the experimental results when the linewidth enhancement factor is 5.5. The simulation also shows that the SOA with large linewidth enhancement factor is preferred to achieve NOR and OR functions with good performance. The input data signal is of good pulsewidth-tolerance for NOR function, whereas not for OR function. The high Q factor could be obtained at narrow pulses injection.     

A theoretical insight into the solid-state optical properties of luminescent materials: the supermolecular approach

The way interchain interactions affect the absorption and luminescence properties of organic conjugated materials is addressed by means of correlated quantum-chemical calculations on molecular aggregates. Special emphasis is given to the influence of chain length and relative positions of the interacting units. The consideration of α -oligothiophenes in their crystalline structure allows us to shed light into the chain-length evolution of the optical splitting of the lowest optically-allowed excited state and to validate the theoretical approach by confronting the theoretical predictions to experimental results. Various strategies are proposed to prevent luminescence quenching when going from solutions to films or crystals.     

Scattering by inhomogeneous particles: microwave analog experiments and comparison to effective medium theories

It is common practice to use effective medium theories (EMT) to estimate average, “effective” optical constants of inhomogeneous materials. A variety of EMTs were developed for different internal structures of the medium and for a variety of shapes, size distributions and physical properties of the inhomogeneities. The most popular EMTs (Maxwell Garnett, Bruggeman, Looyenga, etc.) consider inhomogeneities that are much smaller than the wavelength. The so-called extended EMTs were developed to find effective optical constants in the case of inhomogeneities comparable and slightly larger than the wavelength. This paper compares angular distribution and wavelength dependence of intensity and polarization of scattered light obtained from calculations using the most popular EMTs and extended EMTs with the results of microwave analog measurements at the microwave facilities of the University of Florida. We simulated the light scattering by organic grains with silicate inclusions of size parameter x=0.075 (≈0.01 μm), 0.60 (≈0.1 μm), and 1.24 (≈0.2 μm). The conclusion is that for inclusions of a small size and for a small volume fraction of them in the mixture all EMTs yield similar results and show reasonable agreement with experimental results. The accuracy is better for the angular dependencies of the intensity and of the polarization of the scattered light than for their wavelength dependencies. For inhomogeneities comparable and larger than the wavelength extended EMTs work better but for smaller inclusions non-extended EMTs show more accurate results. Large volume fractions of the inclusions in the mixture (>10%) essentially reduce the accuracy of the results obtained with EMTs. Based on our study we do not recommend to use EMTs in the back-scattering domain and at the scattering angles 30°<θ<70°.     

Equivalence of dual-field theoretical limits of superstring theories

The equivalence of type IA and type IB field-theoretical limits of superstring theories is shown by using a new type of duality transformation. Compactifications of the type IB theory to four dimensions are studied and it is shown that they induce the same vacuum configurations as the type IA theory provided the field equations are satisfied.     

Methods of ellipsometric analysis of polarization optical properties of inhomogeneous surface layers of optoelectronics elements

The basic regularities of changes in the main ellipsometric parameters of a light beam reflected from inhomogeneous surface layers of silicate glasses have been described on the basis of the Drude-Born theories of polarized light reflection. A method of physicomathematical modeling of the refractive index profile in an inhomogeneous surface layer of silicate glasses is reported, which makes it possible to determine, with the lowest second-kind error probability, a model of an inhomogeneous reflecting system that is adequate to the object of study.