Characterization of hardened cylindrical samples using photothermal radiometry

The results of measurements of surface acoustic wave (SAW) humidity sensor with nafion layer are described in the paper. The sensitivity, response time as well as hysteresis for different temperatures have been investigated. The sensor sensitivity, linearity and hystersis are discussd. The results show that such sensor may be suitable for accurate humidity measurements in dry or hot enough environment.     

Characterization of photovoltaic cells using the photothermal deflection spectroscopy

The equilibrium segregation coefficientK ₀ of the following impurities has been measured in high-purity tellurium: Ag, Al, As, Cr, Cu, Fe, In, Mn, Ni, Pb, Pd, Ti, V, and their diffusion coefficient in liquid tellurium determined at 550 °C.     

Theory of two-photon photothermal deflection spectroscopy in stationary and flowing media for arbitrary optical pulse length

A general theory of pulsed two-photon photothermal deflection spectroscopy (PTDS) is presented. We find that there are significant enough differences in the amplitude and temporal evolution of PTDS signals between the results of the single- and two-photon theories that if one tries to interpret two-photon data with single-photon theory, the extracted values may be considerably in error. Our theory is sufficiently general that it incorporates both stationary and flowing media and considers optical pulses of arbitrary length. Moreover, the temporal profile of the optical pulse is explicitly taken into account. The two-photon absorption coefficient is explicitly expressed in terms of oscillator strengths and Clebsch–Gordan coefficients, and the Doppler width for both co-propagating and counter-propagating beams is taken into account. Although the theory is primarily developed for atomic and molecular vapors, it can easily be adapted for condensed matter by expressing the absorption coefficient in terms of the properties of the liquid or solid under investigation. PACS 82.80.Kq; 42.62.Fi; 39.30.+w     

Kinematics of media with continuously changing topology

The fundamental postulate of continuum mechanics states that a body is a three-dimensional differentiable manifold and its motions are diffeomorphisms. Simple thought experiments with cyclic motions of dislocations show that they do not preserve topology (set of neighborhoods). The same is valid for chaotic and turbulent motions with coarse-graining. To describe such motions, kinematics of a generalized continuum mechanics is suggested. Observables are defined operationally in the laboratory system which is not anymore equivalent to the Lagrangian picture. The body is a submanifold of a higher-dimensional space and generalized motions are its diffeomorphisms. In a gauge-theoretic interpretation, the motion is a translational connection with the curvature identified as a dislocation density-flux.     

Modelling optical fibres with arbitrary refractive-index profiles

The characteristics of various models of refractive-index profile are examined. Four models are considered: (1) power-law profile, (2) truncated even polynomial profile, (3) truncated all-term polynomial profile, (4) Gauss-Chebychev approximation. The characteristics of the various models are examined with particular reference to the ray-delay times and the shape of the impulse response. The results show that models (1) and (2) are limited in their usefulness in representing practical profiles, while the approximation (4) is easily applied to a variety of practical profiles.     

Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method

The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics, mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles, arbitrary-shaped liquid-like scatterers, and range-dependent environments. In all cases, the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities(sound pressure and its derivative), by projecting the Helmholtz equation on a constructed orthogonal and complete local basis. The admittance matrix, which is the modal representation of Direchlet-to-Neumann operator, is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes. The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation. The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed. Besides, the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method. It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles, liquid-like scatterers, and range-dependent environments. The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available.     

Determination of binary diffusion coefficients of gases using photothermal deflection technique

A photothermal deflection (PD) technique was applied to measure the binary diffusion coefficients of various gases (CO₂–N₂, CO₂–O₂, N₂–He, O₂–He, and CO₂–He). With an in-house-made Loschmidt diffusion cell, a transverse PD system was employed to measure the time-resolved PD signal associated with the variation of the thermal diffusivity and the temperature coefficient of the refractive index of the gas mixture during the diffusion. The concentration evolution of the gas mixture was deduced from the PD amplitude and phase signals based on our diffraction PD model and was processed using two mass-diffusion models explored in this work for both short- and long-time diffusions to find the diffusion coefficient. An optical fiber oxygen sensor was also used to measure the concentration changes of the mixtures with oxygen. Experimental results demonstrated that the binary diffusion coefficients precisely measured with the PD technique were in agreement with the literature values. Moreover, the PD technique can measure the diffusion coefficients of various gas mixtures with both short- and long-time diffusions. In contrast, the oxygen sensor is only suitable for the long-time diffusion measurements of the gas mixtures with oxygen. PACS 78.20.Nv; 51.20.+d     

Thermal conductivity of PVD TiAlN films using pulsed photothermal reflectance technique

In the present work, we have measured thermal-conductivity of industrial thin film TiAlN with a thickness of around 3 μm. These films are used in machining industry for cutting tools in order to increase their service life. A series of TiAlN coating with a different Al/Ti atomic ratio were deposited on Fe-304 stainless steel (AISI304) substrate by a lateral rotating cathode arc process. The samples were then coated with a 0.8 μm gold layer on top by magnetron sputtering. We present the thermal-conductivity measurement of these samples using pulsed photothermal reflectance (PPR) technique at room temperature. The thermal conductivity of the pure TiN coating is about 11.9 W/mK. A significant decrease in thermal conductivity was found with increasing Al/Ti atomic ratio. A minimum thermal conductivity of about 4.63 W/mK was obtained at the Al/Ti atomic ratio of around 0.72.     

Electromagnetic scattering from a continuously inhomogeneous random medium with cylindrical symmetry

Born's approximation is used to determine the mean value of the turbulent radar cross section (RCS) of an inhomogeneous cylindrical random medium at oblique incidence. The mean medium is taken into account by a renormalization procedure. Then, only the diffraction due to the fluctuating part of the permittivity has to be considered. The fluctuations are approximated by means of the turbulence spectrum given by Kolgomorov's theory. Furthermore, Maxwell's equations are solved in terms of fields rather than potentials. This leads us to a significant reduction of the linear system size which simplifies numerical calculations. It turns out that the fields which propagate in the mean medium are noticeably modified by that medium. Thus, the renormalization has a considerable effect on the assessment of the turbulent RCS of the wake. The influence of the direction of incidence on the RCS levels is also analysed. Finally, numerical results are given in order to compare calculations with experiment.     

Electromagnetic scattering from a continuously inhomogeneous random medium with cylindrical symmetry

Abstract

Born's approximation is used to determine the mean value of the turbulent radar cross section (RCS) of an inhomogeneous cylindrical random medium at oblique incidence. The mean medium is taken into account by a renormalization procedure. Then, only the diffraction due to the fluctuating part of the permittivity has to be considered. The fluctuations are approximated by means of the turbulence spectrum given by Kolgomorov's theory. Furthermore, Maxwell's equations are solved in terms of fields rather than potentials. This leads us to a significant reduction of the linear system size which simplifies numerical calculations. It turns out that the fields which propagate in the mean medium are noticeably modified by that medium. Thus, the renormalization has a considerable effect on the assessment of the turbulent RCS of the wake. The influence of the direction of incidence on the RCS levels is also analysed. Finally, numerical results are given in order to compare calculations with experiment.     

Radio-wave tomography of inhomogeneous media

Results of experimental investigations on radar sensing of inhomogeneous media and objects with the use of both superbroadband (from 0.5 to 17 GHz) multifrequency scanning and supershort nanosecond and subnanosecond radar pulses are considered. It is demonstrated that addition of angular and spatial scanning and subsequent synthesis of a large aperture allow a three-dimensional tomography of low-contrast inhomogeneities to be realized with a spatial resolution of about 1 cm. Examples are presented that confirm a high efficiency of the method for contactless tomography of the forest structure and detection and visualization of infantry mines below a rough sand surface. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 20–25, September, 2006.     

Optical properties of inhomogeneous media

A theory is presented for the optical properties of inhomogeneous media consisting of small particles in a continuous dielectric host. In contrast to the commonly used Maxwell-Garnett approach, our theory includes the dipole-dipole coupling between the randomly distributed particles. The pronounced disorder-induced broadening explains the large width of typical experimental absorption lines and thus resolved the long-standing discrepancy between measured spectra and the predictions of the Maxwell-Garnett model.     

Characterization of inhomogeneous colloidal layers using adapted coherence probe microscopy

Colloidal layers play an important role in environmental studies, for example in the movement of radionuclides in nuclear waste management. New characterization techniques are required for studying such complex, porous layers. The purpose of this work is to adapt coherence probe microscopy (CPM), which is typically used for measuring the surface roughness of single surfaces, to the analysis of thick inhomogeneous colloidal layers. Two types of layers, either composed of 80 nm or 400 nm alumina colloidal particles deposited on glass slides by decantation have been studied. One of the problems in performing routine roughness measurements of colloidal layers using CPM is the appearance of apparent pits below the level of the substrate surface. We demonstrate that this is due to partial detection of the buried colloid/substrate interface. Further, we have developed the “Z-scan” technique, which consists of building up an XYZ image stack by scanning the full depth of the sample. Any point in an XY image can then be investigated to study the local buried internal structure, layer thickness, and effective refractive index. Comparison of results with AFM and SEM confirm the structure found with CPM and the new “Z-scan” technique, which opens up new and useful applications.     

Measurements of third-order nonlinearity of inhomogeneous samples using nonlinear-imaging technique with a phase object

Using electrostatic self-assembly of a [CuPc(COOH)₄]/polydiallyldimethylammonium chloride (PDDA) film, we demonstrate that signal fluctuation induced by a random surface inhomogeneity of less than 70 nm can be approximately resolved by a nonlinear-imaging technique with a phase object (NIT-PO) as opposed to Z-scan. In our NIT-PO simulation the sample is regarded as perfectly parallel, while the incident intensity distribution is modified to mimic that of an extremely weak laser beam traversing the sample, which is detected by a charge-coupled-device (CCD) camera. However, the original phase in the simulations is maintained, since phase distortions caused by the sample are not measurable at the CCD plane. PACS 42.30.Kq; 42.65.-k     

Viscoelastic properties of inhomogeneous media with a fractal structure

The viscoelastic properties of a two-phase medium with a chaotic structure are calculated over the entire concentration range. The conditions for a monotonic and singular behavior of effective viscoelastic properties are established.     

Modal analysis of circular Bragg fibers with arbitrary index profiles

A finite-difference approach based upon the immersed interface method is used to analyze the mode structure of Bragg fibers with arbitrary index profiles. The method allows general propagation constants and eigenmodes to be calculated to a high degree of accuracy, while computation times are kept to a minimum by exploiting sparse matrix algebra. The method is well suited to handle complicated structures comprised of a large number of thin layers with high-index contrast and simultaneously determines multiple eigenmodes without modification.     

X射线在折射率连续变化等离子体介质中的传播

从Maxwell方程出发,得到了X射线光束在非均匀等离子体介质中传播的类衍射积分解,并从理论和数值模拟上着重讨论了折射率梯度效应对光束参数的影响。结果表明,在等离子体电子密度分布较高的区域,梯度效应明显,它直接影响光束的光强分布、衍射效应和光束的偏转程度。     

X射线在折射率连续变化等离子体介质中的传播

 从Maxwell方程出发，得到了X射线光束在非均匀等离子体介质中传播的类衍射积分解，并从理论和数值模拟上着重讨论了折射率梯度效应对光束参数的影响。结果表明，在等离子体电子密度分布较高的区域，梯度效应明显，它直接影响光束的光强分布、衍射效应和光束的偏转程度。