Rayleigh Line Research Articles

Rayleigh scattering and atomic dynamics in dissipative optical lattices.

We investigate Rayleigh scattering in dissipative optical lattices. In particular, following recent proposals [S. Guibal, Phys. Rev. Lett. 78, 4709 (1997)]; C. Jurczak, Phys. Rev. Lett. 77, 1727 (1996)]], we study whether the Rayleigh resonance originates from the diffraction on a density grating and is therefore a probe of transport of atoms in optical lattices. It turns out that this is not the case: the Rayleigh line is instead a measure of the cooling rate, while spatial diffusion contributes to the scattering spectrum with a much broader resonance.

Light scattering and sound propagation in a chemically reacting binary gas mixture

The aim of this paper is to study time-dependent problems like sound propagation and light scattering in binary mixtures undergoing a simple reversible symmetric reaction—of the type A+A⇌B+B—close to the final stage of the chemical reaction where the system tends to chemical equilibrium. The molecules of the gas are modeled as rigid spheres and—apart from the binding (or formation) energy of the molecules—the internal degrees of freedom were not taken into account. The hydrodynamic description is based on the conservation laws of mass, momentum and energy closed by the constitutive equations for the pressure tensor, heat flux vector, diffusion velocity and rate of reaction which correspond to the Navier–Stokes law and generalized laws of Fourier, Fick and Arrhenius, respectively. For the problem of sound propagation it is shown how endothermic and exothermic reactions have influence on the phase speed and on the attenuation coefficient, whereas for the problem of light scattering, their influences on the width of the Rayleigh and Brillouin lines and the position of the Brillouin peak are analyzed.

Detailed features of one-dimensional detonations

The oscillation mechanism and reignition process of one-dimensional unsteady detonations are numerically studied using a one-step chemical reaction model governed by Arrhenius kinetics. A series of simulations, without perturbations from the outflow boundary to the detonation front, are carried out while the degree of overdrive, f, is varied between 1.10 and 1.74 (f=D2/DCJ2; where D is detonation velocity). Shock pressure histories and x–t diagrams are utilized in order to attain precise understanding of the one-dimensional unsteady detonations. At higher degrees of overdrive, f=1.40–1.74, shock pressure histories agree with those of previous studies. The oscillation mechanism is the same as that of the large-disturbance regime of unsteady shock-induced combustion around a projectile. At lower degrees of overdrive, f<1.30, grid resolution affects the eventual results, because half reaction time in the shock pressure exhibits considerable variation. Four typical kinds of oscillation pattern are discussed and are explained by their x–t diagrams and shock pressure histories. Each oscillation mechanism is essentially the same as that of the large-disturbance regime. The reignition process in the failed regime was numerically investigated at f=1.01–1.25. The reignition points tend to converge on a specified point in study of grid refinement, although the oscillation of the shock pressure histories becomes chaotic, suggesting the existence of a unique solution for reignition. All the simulation results for f=1.01–1.20 show the failed regime after initial disturbance at the early stage. The failed regime is compared with the solution of the Riemann problem, and analysis consisting of a Rayleigh line for weak leading shock and a partially burnt Hugoniot curve is adopted. Analysis suggests the concept of partial chemical heat release, indicating the possibility of discontinuous change in conditions, and, indeed, simulation indicates occurrence of explosion. The explosion time derived from the analysis agrees well with the results of simulation.

Raman scattering in amorphous films of In 1− xSe x alloys

Raman scattering (RS) in amorphous films of In 1− x Se x with 0.67± x⩾0.38 has been studied in backscattering geometry with the use of a microscope. Recorded RS spectra are revealing a mixed vibrational density-of-states and molecular character. The spectra spread from the Rayleigh line up to 200–250 cm −1. The bands superimposed on the continua are related to zone center modes of the relevant crystal counterpart, Se–Se or In–In vibrations. The RS spectra suggest the structure of the In 1− x Se x alloys to be the continuous random network built up of In centered tetrahedral clusters with In and Se atoms at the corners. The structure of the Se-rich alloys is similar to 4-2 networks with dominant InSe 4/2 clusters and two-fold coordination of Se bridging atoms. That of the In-rich alloys is expected to resemble 4-3 network with rather strong involvement of In atoms at corner of the In-centered tetrahedral clusters and Se atoms being linked to three In ones.

Ultrabroadband collection and illumination optics for Raman and photoluminescence spectroscopy in the 200–700 nm wave band

The design and construction of an optical instrument is described to enable accurate and reliable resonance Raman scattering and photoluminescence measurements to be acquired in the 200–700 nm (1.77–6.2 eV) wave band, with minimum user intervention between changes of the excitation wavelength. An f/6 line or point focus is formed at the sample. f/2 achromatic catadioptric optics image the scattered light to the entrance slit of an f/7.5 spectrometer. An ultraviolet sensitive charge coupled device camera enables imaging and alignment of samples within the excitation laser region, providing an imaging resolution of better than 13 μm (results presented elsewhere suggest a resolution limit of 7 μm). The use of an aperture plate allows pseudo-confocal operation, leading to considerable improvement in depth discrimination when interrogating extended volume scatterers. This mode of operation furthermore eliminates stray light derived from the Rayleigh line, thereby enabling line focus spectra to be obtained to very low wave numbers. The optics present a unique method of interrogating a sample with an extended lateral and well-defined axial interaction region with a high collection efficiency (optical throughput of >41%), simultaneously offering broadband achromatic spectral response in collection from 200 to 700 nm.

Magnetic instability in a sheared azimuthal flow

We study the magneto-rotational instability of an incompressible flow which rotates with angular velocity (r )= a + b=r 2 where r is the radius and a and b are constants. We nd that an applied magnetic eld destabilises the flow, in agreement with the results of Rudiger & Zhang (2001). We extend the investigation in the region of parameter space which is Rayleigh stable. We also study the instability at values of magnetic Prandtl number which are much larger and smaller than Rudiger & Zhang. Large magnetic Prandtl numbers are motivated by their possible relevance in the central region of galaxies (Kulsrud & Anderson 1992). In this regime we nd that increasing the magnetic Prandtl number greatly enhances the instability; the stability boundary drops below the Rayleigh line and tends toward the solid body rotation line. Very small magnetic Prandtl numbers are motivated by the current MHD dynamo experiments performed using liquid sodium and gallium. Our nding in this regime conrms Rudiger & Zhang's conjecture that the linear magneto-rotational instability and the nonlinear hydrodynamical instability (Richard & Zahn 1999) take place at Reynolds numbers of the same order of magnitude.

Melting Temperature, Brillouin Shift, and Density of States of Nanocrystals

The amplitude of displacement of atoms due to scattering at the surface is calculated. It is found that the zero-point vibrational correction to the mean-square displacement varies as the inverse square of the nanocrystal size and the temperature-dependent part also varies with the nanocrystal size. The melting temperature is found to depend on the nanocrystal size so that smaller melting temperature is obtained for smaller nanocrystals. The phonon−phonon scattering is found to shift the Brillouin line such that as the crystal size reduces, it moves toward the Rayleigh line. The phonon density of states is found to be larger for nanocrystals than for the bulk crystals as it depends on the inverse square of the nanocrystal size.

Structure of liquid solutions near the critical point

Specific features of the structure of the critical state of binary liquid solutions leading to an anomalous behavior of the Rayleigh line due to a dramatic increase in concentration and density fluctuations are considered. It is shown that an experimental treatment must deal with two fluctuation regions near the critical point of solvent vaporization. In the first region, one can achieve a sufficient degree of accuracy by using theories like self-consistent field theory. In the second region, which is closer to the critical point than the first region, scaling theory of second-order phase transitions may be applied. It is found that the anomalous behavior of the Rayleigh line associated with kinetic coefficients is determined by the equilibrium thermodynamic properties and by the radius of fluctuation correlation (rc). A general theory is developed for calculating thermodynamic potentials, especially the chemical potential and its concentration derivative in the fluctuation region. The results of these calculations are compared with the experimental data briefly described in the paper.

Three-dimensional materials analysis by confocal Raman microspectroscopy

Two- and three-dimensional spatial analysis of various composite materials was performed with a scanning confocal Raman microspectrometer. Samples include TiO(2) microparticles, mixtures of polymers, and the surface of an older Eprom computer chip. In the last case both structural and compositional information was obtained by means of comparing the signal intensity of the Rayleigh line with that of the silicon Raman line at 520 cm(-1). The spatial compositions of a pain-relief medicine and a pharmaceutical salt mixture could be visualized from characteristic Raman lines of the components.

Temporal coherence control of Nd:YAG pumped Raman shifter

We study the temporal coherence properties of a Nd:YAG pumped Raman shifter (pump wavelength=355 nm) and report the control of its temporal coherence length z c with hydrogen gas pressure P for different input pump energies E in. Within the range: 3.1⩽ E in⩽6.5 mJ, and for: 0.41⩽ P⩽4.83 MPa, z c exhibits an inverse hump-like dependence with P. The shortest z c occurs near a (critical) pressure P= P c≈0.69 MPa, that is independent of E in. At P= P c, the eight Stokes and anti-Stokes lines exist at their strongest in the Raman output spectrum. For P< P c, a sharp increase in z c is obtained with decreasing P due to the relative dominance of the 355 nm Rayleigh line in output spectrum. For P> P c, a slow increase in z c is observed with P due to the dominance of the second-order Stokes line and the weakening of the anti-Stokes lines that is caused by the deterioration of the phase-matching condition for four-wave mixing.

Temperature dependence of Raman scattering in amorphous films of In 1− xSe x alloys

Raman scattering (RS) in amorphous films of In 1− x Se x with 0.70≥ x≥0.38 has been studied in backscattering geometry with the use of a single channel Raman spectrometer at room and 10 K temperatures. The recorded RS spectra reveal dominant vibrational density-of-states character. They exhibit a continuum, spanning the Rayleigh line up to a shoulder at about 250 cm −1, that moves towards lower frequencies as x decreases from 0.70 to 0.38. The bands at about 104, 125 and at 143 and 237 cm −1 are attributed to In–In, Se 8 ring molecules and Se-chain oscillations, respectively. The structure of In 1− x Se x alloys is deduced to be a continuous random network based on InSe 4/2 tetrahedral clusters interconnected by Se atoms at the shared corners or local Se-chain fragments or Se 8 rings. With growing In content, some Se atoms in such clusters are replaced by In atoms to an extent dependent on In content. The disappearance of the 143 and 237 cm −1 bands in the low temperature spectra taken on the In 0.30Se 0.70 film is attributed to the contraction of interatomic bonds, making conditions favorable for breaking Se polymer chains and Se 8 ring molecule formation.

Ionic contribution to Rayleigh line wing under conditions of light scattering by liquid electrolytic solutions

A theoretical treatment is performed of the mechanism (suggested in N. F. Bunkin andA. V. Lobeev, Z. Phys. Chem. 214, 269 (2000)) of ionic effect on the Rayleigh line wing under conditions of light scattering by liquid electrolytic solutions. The mechanism consists essentially in that the fluctuation electric field caused by Brownian motion of ions dissolved in a liquid leads, because of the Kerr polarization effect, to fluctuations of optical anisotropy of the scattering medium. The spectral characteristics of the Rayleigh line wing are obtained using the fluctuation-dissipative theorem as applied to equilibrium thermal electromagnetic field. Expressions are derived for the integral intensity and spectral width (Δν) of the Rayleigh line wing in terms of parameters of liquid solution such as the temperature T, the viscosity η, the concentration of dissolved ions ni, and the coefficient of their diffusion Di. It is demonstrated that Δν ∝ exp(−W/2T), where W is the activation energy of ion mobility bi = Di/T. The possible region of validity of developed theoretical concepts as applied to the experimental data for the Rayleigh line wing in electrolytic solutions is discussed.

Concentration Phase Transitions and Structural Disordering in the System of Solid Solutions LixNa1−xTa0.1Nb0.9O3

Concentration phase transitions and structural disordering in the system of solid solutions LixNa1−xTa0.1Nb0.9O3 (x = 0–0.16) are investigated by the methods of Raman scattering, x–ray structural analysis, and electrophysical measurements. Points of disruption of the translational order in the arrangement of cations at x = 0.05–0.06, 0.09, 0.11, 0.135, and 0.14 that correspond to the boundaries of morphotropic regions and concentration structural anomalies are detected. At points x = 0.11; 0.135, and 0.14, the Raman spectrum in the region of vibrations of the cations located in octahedral and cubooctahedral holes (0–400 cm−1) consists of two wide maxima and is practically smeared into the wing of the Rayleigh line, and on the concentration dependences of the electrophysical properties one observes sharp anomalies. The oxygen ochahedrons are distorted less significantly as x changes: the corresponding lines broaden, and new lines demonstrating a symmetry change of the oxygen octahedrons appear only for x ≥ 0.14. It is shown that the system of solid solutions LixNa1−xTa0.1Nb0.9O3 for x < 0.015 is characterized by the antiferroelectric type of dipole ordering, and for x ≥ 0.015 the structure of a solid solution becomes noncentrosymmetric.

Resonance Raman scattering in photonic band-gap materials

We study the resonance Raman scattering of light from a three-level atom embedded in a photonic band-gap material or in a frequency dispersive medium whose photon spectrum exhibits a gap due to photon coupling to medium excitations such as excitons and optical phonons. We demonstrate that the one-particle spectrum of the system consists of either a continuous part with energy lying outside the gap or a single discrete mode with energy lying inside the gap. The discrete mode, which occurs when both of the allowed atomic transitions of the $\ensuremath{\Lambda}$ configuration lie inside the gap, can be treated as a photon-atom bound state in which the radiation is localized in the vicinity of the atom. In the case of the continuous spectrum, the Rayleigh and Stokes lines are shifted as well as narrowed (or broadened) as the corresponding transition frequencies are shifted relative to the upper band edge, providing a distinctive experimental signature of atom-photon interactions near a photonic band edge.

Experimental and Predicted Detonation Parameters for Liquid-Phase H2O2/H2O Mixtures

We report the measured failure diameter and a detonation speed for the liquid explosive mixture 90.5/9.5 wt % H2O2/H2O confined in thick seamless 304 stainless steel tubing and fired at ca. 30 °C. The detonation speed datum and knowledge of the diameter effect curves of other liquid explosives are used to estimate the infinite-medium (i.e., planewave) detonation speed of this material. Ambient condition sound speed measurements and the universal liquid Hugoniot form are used to obtain the unreacted Hugoniot of the 90.5/9.5 wt % H2O2/H2O mixture. This Hugoniot and the Rayleigh line obtained from the estimated infinite-medium detonation wave speed are used to predict the von Neumann spike pressure of the material. Estimates of the fully reacted (i.e., products) Hugoniot, the Chapman−Jouguet (CJ) detonation pressure, and CJ detonation speed for other H2O2/H2O mixtures are obtained using the CHEETAH equilibrium thermochemical code. Predictions of the infinite-medium detonation speed and the von Neumann spike ...

Low-energy excitations in stressed poly(methyl methacrylate)

Raman study of flexure stressed poly(methyl methacrylate) (PMMA) plates at the frequency range of libration mode (80 cm−1), boson peak (14 cm−1), and quasi-elastic light scattering (QLS) (below 20 cm−1) is presented. The reversible changes in the vicinity of the Rayleigh line were attributed to partial disturbance of the midrange order due to stress-induced redistribution of random fluctuations of orientation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1133–1136, 2000

Low-energy excitations in stressed poly(methyl methacrylate)

Raman study of flexure stressed poly(methyl methacrylate) (PMMA) plates at the frequency range of libration mode (80 cm−1), boson peak (14 cm−1), and quasi-elastic light scattering (QLS) (below 20 cm−1) is presented. The reversible changes in the vicinity of the Rayleigh line were attributed to partial disturbance of the midrange order due to stress-induced redistribution of random fluctuations of orientation. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1133–1136, 2000

Raman scattering in In 2Se 3 and InSe 2 amorphous films

Raman scattering (RS) in both In 2Se 3 and InSe 2 amorphous films has been studied by micro-Raman in backscattering geometry at room temperature. The 40 μm thick films were prepared by thermal vacuum deposition onto a borosilicate glass substrate. The In 2Se 3 amorphous film was stripped off from the substrate. The recorded Raman spectra of both amorphous films reveal a general phonon density-of-states character, though some contribution of molecular-like character in the case of In 2Se 3 amorphous film is observed. The Raman spectra of In 2Se 3 film appear to be related to that of the α-In 2Se 3 crystal, while those of InSe 2 seem to be related to the γ-In 2Se 3 crystal. The peaks in the frequency range from the Rayleigh line up to about 240 cm −1 are attributed to the folding of TA–LA and TO–LO crystal related modes. The strongest feature at 254 cm −1 and a shoulder at 235 cm −1 in the Raman spectrum of In 2Se 3 film are attributed to Se 8 rings and Se n polymer molecules, while the one at 490 cm −1 is assigned to a second order contribution. The 150 cm −1 feature in InSe 2 a-film is related to the zone center mode of the γ-In 2Se 3 crystal. The Raman spectra suggest that the structure of In 2Se 3 film is composed of linked InSe 4 tetrahedral clusters with locally distributed Se n polymer and Se 8 ring molecules. For InSe 2, the structure of the film seems to be composed of InSe 4 clusters linked by Se atoms at the corners shared by two vicinal tetrahedra.

The prediction and discovery of Rayleigh line fine structure

The history of the theoretical prediction and experimental discovery of the Rayleigh line fine structure (which belongs to one of the most important phenomena in optics and physics of condensed matter) is discussed along with the history of first publications concerning this topic.

Quasi-elastic light scattering and the solitonic phase in betaine calcium chloride dihydrate (BCCD)

The temperature (40K ≤ T ≤ 200K) and polarization dependence (z(yy)x, z(xz)x) of the integrated intensities of quasi-elastically scattered light (λ = 514.5 nm) in a wavenumber interval of (0 ± 3) cm−1 around the Rayleigh line at the different phase transitions in single crystals of BCCD have been observed. Large anomalies (central peaks) are observed at the transitions into the ferroelectric, the various commensurate (c, c′), and the incommensurate phases. The widths of the anomalies on the temperature scale differ considerably, they are large in the region of quasi-harmonic modulation but narrow in the region of square-wave modulation (solitonic phase), where unusual shapes on the T-axis are displayed. The scattering phenomena at low temperatures are hypothetically interpreted by the formation or rearrangement of domain walls (solitons). The c-c′ transitions are of the order-disorder type.