Case Of Specular Reflection Research Articles

Rigorous theory of thin-vapor-layer linear optical properties: The case of specular reflection of atoms colliding with the walls

The theory of the thin vapor layers linear optical properties is presented for the case of specular reflection of atoms colliding with the walls. The effects of light absorption and the shift in the resonance frequency are taken into account by means of self-consistent calculation of the field and polarization in a gaseous medium. The obtained formulas reproduce the complex dependence of the spectral line profile on the gas layer thickness and allow one to determine numerically the exact values of the blueshift.

Synergy of the ray tracing+carrier transport approach: On efficiency of perovskite solar cells with a back reflector

We investigate the absorptance and the power conversion efficiency of a perovskite thin-film solar cell at a specular and Lambertian reflection on the cell's back-surface reflector. The analysis is done by means of the Monte-Carlo ray tracing simulations, complemented by the transfer-matrix method to account for the interference phenomenon in the local generation rate G(z) of carriers inside the semiconductor. This function is employed further in the transport equations to calculate the current-voltage characteristics of the cell. Taking the perovskite absorber CH3NH3PbI3 as an example, we analyse its efficiency, altering the absorber thickness in the interval 50 ÷ 1000 nm. We find that in the cell (∼200 nm) the enhanced photon absorption due to the Lambertian reflection yields the efficiency increase on 2.2% as opposed to the specular reflection case. Moreover, the maximum efficiency, obtained for the perovskite layer of the thickness ∼150 nm, exceeds the one obtained for the perovskite layer of the thickness ∼500 nm with the specular reflection.

Measuring and Modeling the Growth Dynamics of Self-Catalyzed GaP Nanowire Arrays.

The bottom-up fabrication of regular nanowire (NW) arrays on a masked substrate is technologically relevant, but the growth dynamic is rather complex due to the superposition of severe shadowing effects that vary with array pitch, NW diameter, NW height, and growth duration. By inserting GaAsP marker layers at a regular time interval during the growth of a self-catalyzed GaP NW array, we are able to retrieve precisely the time evolution of the diameter and height of a single NW. We then propose a simple numerical scheme which fully computes shadowing effects at play in infinite arrays of NWs. By confronting the simulated and experimental results, we infer that re-emission of Ga from the mask is necessary to sustain the NW growth while Ga migration on the mask must be negligible. When compared to random cosine or random uniform re-emission from the mask, the simple case of specular reflection on the mask gives the most accurate account of the Ga balance during the growth.

Velocity Reversal Criterion of a Body Immersed in a Sea of Particles

We consider a rigid body colliding with a continuum of particles. We assume that the body is moving at a velocity close to an equilibrium velocity V_{\infty} and that the particles colliding with the body reflect diffusely, that is, probabilistically with some probablility distribution K. We find a condition that is sufficient and almost necessary that the collective force of the colliding particles reverses the relative velocity V(t) of the body, that is, changes the sign of V(t)-V_{\infty}, before the body approaches equilibrium. Examples of both reversal and irreversal are given. This is in strong contrast with the pure specular reflection case in which only reversal happens.

Modeling and shaping specular and diffuse reflection sound fields in enclosures.

Steady‐state sound fields in enclosures, with specular and diffuse reflection boundaries, are modeled with an energy‐intensity boundary element method using uncorrelated broadband directional sources. The specular reflection case is solved using an iterative relaxation method extended from a 3‐D diffuse reflection solution. When chosen properly, only a few directivity harmonics are required. Starting with a diffuse calculation, higher harmonicsare estimated by post‐processing, and the original diffuse influence matrix is refined accordingly and converges in a few relaxation steps. The method is higher‐order accurate, computationally efficient, and similar to the diffuse case in that it includes strict enforcement of energy conservation. The simulations give accurate results compared to exact modal solutions. Sample calculations are presented to show that the mean‐square pressure spatial variation can be tailored using a combination of diffuse and specular surfaces for the design of acoustic spaces.

Modeling specular reflection in enclosures with energy-intensity boundary elements and an iterative relaxation method.

Steady-state sound fields in enclosures with specular reflection boundaries are modeled by an energy-intensity boundary element method using uncorrelated broadband directional sources. The specular reflection case is solved using an iterative relaxation method extended from a three dimensional (3-D) diffuse reflection solution. When chosen properly, few directivity harmonics are required. Starting with a diffuse calculation, higher harmonics are estimated by post-processing, and the original diffuse influence matrix is refined accordingly and converges in few relaxation steps. The method is higher-order accurate and similar to the diffuse case in that it includes strict enforcement of energy conservation. The method is computationally efficient, making it useful for the design of acoustic spaces. This new 3-D energy-intensity boundary element method utilizes an absorption scaling theory, allowing for direct solution of the element power distribution that describes the primary spatial variation caused by the effects of specular reflection, the absorption dependence on incidence angle, and the non-uniform spatial distribution of absorption and input power in the enclosure. Sample results show that differences between diffuse and specular solutions are often fairly small. The iterative relaxation method, with a limited number of specular harmonics, appears to provide a reasonable approach in practice. [Sponsored by NSF.]

Diffraction Corrections to Fields Specularly Reflected by a Smooth 2-D Surface

Diffraction corrections to the geometric optics results were derived for a general case of specular reflection from a smooth, perfectly conducting 2-D body. The general equations are applied to the specific case when the surface directrix in the vicinity of the specular point can be approximated by the arc of the conic section curve (parabola, circle, ellipse, or hyperbola). These results extend upon the ones obtained earlier for backscattering only (I. M. Fuks, IEEE Trans. Antennas Propag., vol. 53, no. 5, pp. 1653-62, 2005) to the general case of bistatic scattering at arbitrary incidence angles

Transport Properties of Two-Dimensional Wigner Solid on Free Surface of Liquid3He–4He Mixtures

The Wigner solid (WS) transport over dilute solutions of 3 He in 4 He is theoretically studied in a wide range of temperatures. It is shown that for solution concentrations \(x \gtrsim 1\)%, the WS mobility should be limited by bulk 3 He quasiparticle reflection from the sublattice of surface dimples. The formation of a surface layer of 3 He atoms affects the WS resistivity in two different ways. First, it increases the depth of surface dimples and the kinetic friction with cooling. At the same time, it introduces the unusual diffusive reflection for bulk quasiparticles at the free surface that strongly reduces the kinetic friction, as compared with the case of specular reflection. The analysis presented indicates that the WS can be used as a sensitive probe for the bulk and surface 3 He impurity subsystems.

Regularity for the Vlasov--Poisson System in a Convex Domain

We consider the initial-boundary value problem in a convex domain for the Vlasov--Poisson system. Boundary effects play an important role in such physical problems that are modeled by the Vlasov--Poisson system. We establish the global existence of classical solutions with regular initial boundary data under the absorbing boundary condition. We also prove that regular symmetric initial data lead to unique classical solutions for all time in the specular reflection case.

An integral equation basic to the BGK model for flow in a cylindrical tube

The classical BGK model for describing the flow of a rarefied gas in a cylindrical tube is used as a starting point for developing an equivalent integral-equation formulation of the considered class of problems. While the problems of Poiseuille flow and thermal creep in a cylindrical tube have already been well solved in terms of a pseudo problem obtained from an integral-equation definition of the problems, the development of the relevant integral equation is given here for a larger class of problems. In particular it is noted that a general inhomogeneous source term in the balance equation and a general inhomogeneous term in the boundary condition are both included in the considered model, and, as a special case, the integral-equation formulation for the case of specular reflection at the surface of the tube is also developed.

Enhanced electron heating in diffuse reflection by a plasma boundary

Dense plasma heating by an ultrashort laser pulse is investigated in the regime of the high-frequency skin-effect. It is shown that the diffuse electron reflection by the plasma boundary yields a significant increase of electron temperature as compared to the specular reflection case, and a faster propagation of the heat flux inside the plasma.

Resistance of motion to a small, hypervelocity sphere, sputtering through a gas

Earlier work on the resistance acting on a small sphere moving through a gas is reviewed. A model for the resistance encountered by a sphere, the surface molecules of which are sputtered off during collisions with the gas molecules, is derived and compared with the case of specular reflection. The sputtering model is applied to the case of small 10-μm radius meteoroids entering the Earth's atmosphere. A possible link between the results obtained and the recent discovery of unheated, organic grains at an altitude of 40 km in the Earth's atmosphere is considered.

Low-temperature properties and specific anisotropy of pure anisotropically paired superconductors.

Dependences of low temperature behavior and anisotropy of various physical quantities for pure unconventional superconductors upon a particular form of momentum direction dependence for the superconducting order parameter (within the framework of the same symmetry type of superconducting pairing) are considered. A special attention is drawn to the possibility of different multiplicities of the nodes of the order parameter under their fixed positions on the Fermi surface, which are governed by symmetry. The problem of an unambiguous identification of a type of superconducting pairing on the basis of corresponding experimental results is discussed. Quasiparticle density of states at low energy for both homogeneous and mixed states, the low temperature dependences of the specific heat, penetration depth and thermal conductivity, the I-V curves of SS and NS tunnel junctions at low voltages are examined. A specific anisotropy of the boundary conditions for unconventional superconducting order parameter near $T_c$ for the case of specular reflection from the boundary is also investigated.

Multiple scattering in the interaction of low energy ions with a cold Au surface covered by a film of condensed argon

Energy spectra of ions emitted from a cold (< 40 K) Au surface covered by a thin film of condensed argon at small scattering angles (including the case of specular reflection) were examined. Depending on the density of the film new effects such as a splitting or shifting of the gold quasi-single-scattering peak are observed. It is postulated that these effects are connected with multiple scattering of projectiles inside the adsorbed film. Multiple scattering directs the ions to the detector after single scattering from the substrate atoms over the angles larger or smaller than the detection angle. At a certain density of adsorbed film only large-angle substrate scattering occurs. This phenomenon is manifested experimentally by a shift of the gold quasi-single-scattering peak.

A role of multiple scattering in the interaction of low energy ions with a cold Au surface covered by a film of condensed xenon

Energy spectra of ions emitted from a cold Au surface covered by a thin film of condensed xenon in the range of small scattering angles (including the case of specular reflection) were measured. If the concentration of particles in adsorbed film and its thickness are relatively small, new scattering effects such as a splitting and shifting of ‘single scattering peaks’, are observed. These effects are connected with multiple scattering of ions inside the adsorbed film of condensed xenon.

Multiple nondissociative scattering of molecules and multiple scattering of ions from a cold metal surface covered with krypton film

Energy spectra of ions emitted from a cold Au surface covered by condensed krypton film at small detection angles θ (including the case of specular reflection) under deuterium-molecule ion bombardment were measured. Two maxima on the energy scale (near the primary energy) were found, and their relative intensity changed according to the law: I 21 ∼ θ −7. Since multiple scattering theory of molecules predicts such a dependence, it is assumed that the observed maxima are connected with multiple nondissociative scattering of D 2 + molecules inside the krypton surface film. Additional experiments with Ar + ion scattering under the same conditions show a splitting of the quasi-single-scattering peak of gold due to multiple scattering of argon ions inside the krypton layer. The maxima in the deuterium energy spectra demonstrate multiple scattering events as well.

Electron resonance reflections from perfect crystal surfaces and surfaces with steps

Dynamical calculations are carried out to investigate the creation processes of reflection waves under the (660) specular reflection case of GaAs (110) in the geometry of reflection high energy electron diffraction (RHEED). It is shown that the resonance waves are localized at the top two to three atomic surface layers. The monolayer resonance characteristic happens only at some specified low angle incidence cases but not in general. Most of the reflection intensity in the RHEED pattern is created while the electrons are propagating along the surface. The probability of immediate reflections of electrons from a surface is small. This is the reason that the resonance excitation of a surface can greatly enhance the total reflectance of a surface. The propagation of a electron beam at a crystal surface can be characterized by a mean travelling distance, which is 500 to 700 Å for GaAs (110). It is pointed out that a column approximation may not be a good treatment for RHEED calculations. Dynamical calculations for surfaces with steps show that the one-atom-high down-step can critically interrupt the resonance propagation of the resonance wave along the surface. The interrupted wave goes out of the surface and forms some “extra” spots in the RHEED pattern, which are observed in RHEED experiments in a scanning transmission electron microscope. This confirms the existence of surface resonance waves and their oscillating propagations along crystal surfaces.

The Sommerfeld half‐plane problem revisited, IV: Variations on a theme of Carlson and Heins

AbstractA plane wave is incident upon an infinite set of equally spaced, semi‐infinite parallel and staggered plates. The boundary conditions on the plates alternate between the Dirichlet and Neumann ones. This problem is formulated as a pair of coupled Wiener‐Hopf integral equations and solved by a method proposed by A. E. Heins in 1950. For the case of specular reflection, that is, a single reflected plane wave, the magnitudes of the reflection coefficient and the transmission coefficients are determined.

Reversal of the wavefront of the second harmonic of YAG laser radiation used in atmospheric sounding

An analysis was made of reversed second harmonic radiation of a YAG laser traveling opposite to radiation probing an inhomogeneous medium (static and dynamic model media, turbulent atmosphere). The characteristics of the recorded radiation (angular spectrum, dispersion of the intensity fluctuations) are compared with the case of specular reflection and wavefront reversal without a change in the optical frequency.

Coupling of rayleigh-like waves with zero-sound modes in normal3He

The Landau kinetic equation is solved in the collisionless regime for a sample of normal3He excited by a surface perturbation of arbitrary ω andk. The boundary condition for the nonequilibrium particle distribution is determined for the case of specular reflection of the elementary excitations at the interface. Using the above solution, the energy flux through the boundary is obtained as a function of the surface wave velocity ω/k. The absorption spectrum and its frequency derivative are calculated numerically for typical values of temperature and pressure. The spectrum displays a sharp, resonant-like maximum concentrated at the longitudinal sound velocity and a sharp maximum of the derivative concentrated at the transverse sound velocity. The energy transfer is cut off discontinuously below the Fermi velocity. An experimental measurement of the energy transfer spectrum would permit a determination of both zero-sound velocities and the Fermi velocity with spectroscopic precision.