Calculation of discrete and resonant states of Coulomb acceptor in HgCdTe alloys

The energies and wavefunctions of both localized and resonant states are calculated for Coulomb acceptor in narrow-gap HgCdTe alloys with cadmium mole fraction from 0 to 30%. The simulation is performed with scattering matrix method within a spherically-symmetric three-band Kane model that takes into account the conduction band and two valence bands. The energies of both localized and resonant states are determined using the localization rate magnitude, introduced in this work.

Synthesis of highly efficient multilayer dielectric diffraction gratings for spectral combining of laser beams

Статья посвящена синтезу многослойных диэлектрических отражательных дифракционных решеток, с высокой эффективностью обеспечивающих спектральное сложение пучков с различной длиной волны в заданном дифракционном порядке. Приводятся результаты решения задачи синтеза многослойных диэлектрических дифракционных решеток, обеспечивающих спектральное сложение в первом или минус первом порядке дифракции. Кроме того, решается задача синтеза для таких решеток с учетом возможных технологических ограничений на высоту профиля (глубину травления). Решение задачи синтеза проводится путем минимизации зависящего от параметров решетки целевого функционала методом Нелдера-Мида. Решение прямой задачи на каждом шаге минимизации осуществляется при помощи комбинации неполного метода Галеркина и метода матриц рассеяния. The paper is devoted to the synthesis of multilayer dielectric reflection diffraction gratings providing high-efficiency spectral combining of the beams with different wavelengths in a given diffraction order. The results are presented for solving the synthesis problems for multilayer dielectric diffraction gratings providing spectral combining in the first or minus first diffraction order. Besides, the synthesis problem for such gratings is solved with account taken of possible technological constraints imposed by the height of the grating profile (etch depth). The solution of the synthesis problem is obtained by means of Nelder-Mead minimization of the merit function depending on the grating parameters. At each minimization step the direct problem is solved using a combination of the incomplete Galerkin method and scattering matrix method.

Generalized scattering matrix method for Lamb wave scattering analysis at cascaded notches

A thorough understanding of the scattering mechanism of Lamb waves at discontinuities is of interest for quantitative evaluation of structural properties and mode control. This study extends the generalized scattering matrix method to investigate the interaction of straight crested Lamb waves with multiple cascaded rectangular notches. Based on the orthogonality and completeness of Lamb modes, the mode matching method is utilized to determine the scattering matrices of downward and upward step discontinuities. After that, the generalized scattering matrix method is employed to determine the scattering matrices of a single rectangular notch and the recurrence relations between the scattering matrices of n + 1 cascaded notches and those of n cascaded notches. Finally, the scattering matrices of multiple cascaded notches can be easily obtained taking advantage of the recurrence relations. As the number of cascaded notches increases, more and sharper peaks appear in the scattering coefficient curves. The finite element simulations conducted in the time domain validate the theoretical results for cascaded notches with identical or different depths, which demonstrate that this method can be applied to find the scattering coefficients at piece-wise periodic or nonperiodic waveguides. The generalized scattering matrix method may have potential applications in quantitative nondestructive evaluation and mode control.

Experimental Investigation of Acoustic Characteristic on Orifice Shaped With Bias Flow

Combustion dynamics has been a significant problem for a lean, premixed, prevaporized (LPP) combustor. Understanding the acoustic characteristics of combustor components is essential to modeling thermoacoustic behavior in a gas turbine combustion system. Acoustic characteristics such as impedance and scattering matrix elements are experimentally determined for different-shape orifices with an emphasis on the effect of the flow field on them. These orifices are used to represent premixed swirl cups in LP combustors. The validity and limitation of two different methodologies are evaluated by comparing measured results with those of others. Consistent with analytical predictions, the measured resistance through an orifice increases as the bias flow increases. Different types of orifices considered in this study behave similarly to a thin orifice at high bias flow even though the discharge coefficients vary as much as 30% between them. The conventional method produces impedance values independent of waves reflected from the end boundary condition only when the scattering elements at the orifice downstream are roughly equal to those upstream of the orifice. However, the scattering matrix method produces impedance values that are not affected by the source or reflected waves at the system’s boundary. The scattering matrix measurements show that the reflection and transmission elements increases and decreases, respectively, as the bias flow through an orifice increases.

Study on the Propagation Characteristics of Terahertz Waves in Dusty Plasma with a Ceramic Substrate by the Scattering Matrix Method

The propagation characteristics of terahertz (THz) waves incident vertically into inhomogeneous and collisional dusty plasma with a ceramic substrate are studied using the scattering matrix method (SMM). The effects of the incident wave frequency and plasma parameters, such as the maximal electron density, dust particle density, dust particle radius and collision frequency, on the reflectance and transmittance of THz waves in the dusty plasma are discussed. In addition, the differences of the propagation properties in the dusty plasma, with and without ceramic substrate, are analyzed. Meanwhile, the differences of the propagation properties in dusty plasma and common plasma, respectively, with ceramic substrate are also compared. Simulation results show that the substrate and dust particles have significant influence on the propagation characteristics of THz wave in plasma sheath. Finally, the transmission increases with the increase of electron density, dust density, dust particle radius and collision frequency.

Расчет температурной зависимости энергии состояний кулоновского акцептора в узкозонном твердом растворе HgCdTe

Localized and resonant state energies of coulomb acceptor in narrow-gap HgCdTe alloy are calculated at different temperatures. A universal technique for estimation of localized and resonant state energies is suggested. It is shown theoretically that these energies are туфкдн constant in a wide range of temperatures from 0 to 100 K. The simulation is performed with scattering matrix method within spherically-symmetric three-band Kane model that takes into account the conduction band two valence bands.