Showing papers on "Brillouin zone published in 1980"
TL;DR: Estimates of the real and imaginary parts M′ and M″ of the longitudinal bulk modulus have been made for the first time and offer opportunities for probing the lens and its proteins topographically as a function of growth.
Abstract: Brillouin spectra of biological systems may ultimately be related to their intrinsic molecular properties. In some instances the optical properties may be associated with the elastic ones and ultimately with the force constants of the molecules involved1,2. In the present work we have used a triple-pass Fabry–Perot interferometer to measure Brillouin light scattering spectra for refractive tissues of the eye, including cornea, capsule and lens. Combined with corresponding measurements of density, estimates of the real and imaginary parts M′ and M″ of the longitudinal bulk modulus have been made for the first time. Measurements have extended over four classes of vertebrate: Mammalia, Aves, Pisces and Amphibia; only small differences have been found between the various samples of cornea, whereas marked differences occur between the different lenses. Hence this account concentrates largely on the latter. The implications of this work lie not so much at the opthalmological level as at the macromolecular and offer, in conjunction with other scattering techniques, opportunities for probing the lens and its proteins topographically as a function of growth.
177 citations
TL;DR: In this paper, the Brillouin theorem was used to optimise the orbitals in a general multi-structure valence-bond wave function, and the resulting VB SCF method is a powerful generalisation of MC SCF to permit the use of non-orthogonal orbitals.
133 citations
TL;DR: The surface phonons of metals at certain points of the two-dimensional Brillouin zone can be observed in electron energy-loss spectroscopy when suitable coupling is provided by commensurable adsorbate lattices.
Abstract: Surface phonons of metals at certain points of the two-dimensional Brillouin zone can be observed in electron energy-loss spectroscopy when suitable coupling is provided by commensurable adsorbate lattices.
129 citations
TL;DR: In this article, the Brillouin spectra of binary and ternary silicate glasses were investigated and absolute values for the Pockets coefficients p12 and p44 and (p11 and p12) were calculated from the measured spectra.
Abstract: The Brillouin spectra of binary and ternary silicate glasses were investigated and absolute values for the Pockets coefficients p12 and p44 and (p11 – p12) were calculated from the measured spectra The results were interpreted as to the density and refractive index dependence of the Pockels coefficients in terms of the theoretical treatments by Carleton, Mueller and Sipe From the measured p12 and p44 values the quantity (ϱ∂ϵ/∂p), the change of the dielectric constant with respect to density, was calculated and compared with (ϱ∂ϵ/∂ϱ) evaluated from the Lorentz-Lorenz equation, Drude equation and the Carleton model The Lorentz-Lorenz and Drude equations overestimated the magnitude of (ϱ∂ϵ/∂ϱ), while the Carleton model with its two limiting cases set upper and lowe bounds to (ϱ∂ϵ/∂ϱ) From the (ϱ∂ϵ/∂ϱ) results the strain polarizability constant (λ0) was determined and its physical significance discussed In general, the alkali-oxide concentration dependence of the Pockels coefficients of various silicate glasses has been measured and qualitatively explained by several existing theoretical formulations
81 citations
TL;DR: In this article, Raman experiments on polar phonons in GaAs•Ga1−xAlxAs superlattices are reported. And the interpretation in terms of folding of the phonon Brillouin zone and scattering from q≠0 phonons induced by electronic zone folding is discussed.
Abstract: Raman experiments on polar phonons in GaAs‐Ga1−xAlxAs superlattices are reported. Other data from the literature, and its interpretation in terms of folding of the phonon Brillouin zone and scattering from q≠0 phonons induced by electronic zone folding, are discussed. An alternative explanation is presented based on optical anisotropy induced by layering. Numerical results show good agreement with experiment.
79 citations
TL;DR: Very low-angle Brillouin light-scattering experiments have been performed in liquid water subjected to a temperature gradient as mentioned in this paper, and both the sign and the order of magnitude of this effect agree with recent theoretical calculations for nonequilibrium systems.
Abstract: Very-low-angle Brillouin light-scattering experiments have been performed in liquid water subjected to a temperature gradient. The line intensities are unequal, and both the sign and the order of magnitude of this effect agree with recent theoretical calculations for nonequilibrium systems.
77 citations
TL;DR: In this article, a detailed theory of the scattering of light by acoustic surface ripples arising from both bulk and surface phonons in solids is given, and the measured Brillouin spectra of Al, Ni, GaAs and GaP are presented.
Abstract: A detailed theory of the scattering of light by acoustic surface ripples arising from both bulk and surface phonons in solids is given. The measured Brillouin spectra of Al, Ni, GaAs and GaP are presented. The experimental results are compared with theoretical predictions for the ripple scattering mechanism. This mechanism is dominant for Al and Ni, where there is good agreement between theory and experiment for the spectral distribution and angular dependence of the intensity, but poor agreement for the absolute cross section. The alternative scattering mechanism by way of the elasto-optic effect is shown to be important in GaAs and GaP, although in the latter the scattering from surface phonons is still apparently dominated by the ripple mechanism.
73 citations
TL;DR: In this article, the lattice instability of 1 T -TiSe 2 was studied on the basis of the electronic band structure of this compound obtained by a tight-binding fit to the Zunger and Freeman's band.
Abstract: Lattice instability of 1 T -TiSe 2 is studied on the basis of the electronic band structure of this compound obtained by a tight-binding fit to the Zunger and Freeman's band. The electronic susceptibility, for which the wave number dependence of electron-lattice matrix elements is taken into account, is calculated for several phonon modes of wave vectors at the M and L points in the Brillouin zone. The results are discussed in connection with the lattice instability.
56 citations
TL;DR: In this paper, the effects of magnetic field on the stimulated Brillouin and Raman scattering processes are studied for CO2 laser plasmas and toroidal systems by an extraordinary electromagnetic wave.
Abstract: The effects of magnetic field on the stimulated Brillouin and Raman scattering processes are studied. The formalism applies to plasmas produced by CO2 lasers and to electron cyclotron heating of toroidal systems by an extraordinary electromagnetic wave. In the case of laser fusion the plasma is magnetized due to the self‐generated dc magnetic field, while in toroidal plasmas it is due to the external magnetic field. The magnetic field greatly reduces the threshold for Brillouin backscattering by the lower hybrid wave. The Raman scattering by the upper hybrid wave has substantial growth rate even for large kλD because of the reduction of linear Landau damping due to the magnetic field.
52 citations
TL;DR: In this paper, simple models are used to provide nonlinear estimates of Brillouin scatter in several complementary regimes and some applications to laser plasma interactions are given, including laser plasma interaction.
Abstract: Simple models are used to provide nonlinear estimates of Brillouin scatter in several complementary regimes. Some applications to laser plasma interactions are given.
49 citations
TL;DR: In this article, the question of accuracy obtainable in density-of-states and Fermi-energy evaluations in disordered alloys by using various direction sets is discussed, and results on the simple cubic tight-binding band and on the model Hamiltonian for Cu are considered.
Abstract: We present several large sets of special directions for cubic lattices. The question of accuracy obtainable in density-of-states and Fermi-energy evaluations in disordered alloys by using various direction sets is discussed. In this context, results on the simple cubic tight-binding band and on the model Hamiltonian for Cu are considered.
TL;DR: In this article, the Rayleigh-Brillouin spectrum of He, Ne, and Ar is reported for 90mmode + √ √ − √ +√ −√ -degree scattering at a number of densities spanning the kinetic and hydrodynamic regime.
Abstract: The Rayleigh-Brillouin spectrum of He, Ne, and Ar is reported for 90\ifmmode^\circ\else\textdegree\fi{} scattering at a number of densities spanning the kinetic and hydrodynamic regime. A purely experimental test of scaling is made and it is found that deviations from scaling at high density can be attributed to mean-field effects. At low densities there is evidence that deviations from scaling, which arise from the detailed dependence of the spectrum on the intermolecular potential, are detectable at the few percent level. Some insight into scaling is obtained by comparing the results at low densities with curves predicted from a $3E$ kinetic model and from hydrodynamic theory.
TL;DR: In this paper, a straightforward application of the surface Green function matching method to the surface wave problem is presented. But these results cannot explain some remaining discrepancies between Brillouin scattering data on one hand and ultrasonic experimental data as well as theoretical calculations on the other hand.
TL;DR: In this paper, a system in which many laser shots are used to build up one Brillouin spectrum for each range gate in an ocean subsurface experiment is described, where the laser beam is used to acquire the three-dimensional information (frequency, depth, and intensity) required for a range resolved spectrum, either multichannel or integration technique must be employed.
Abstract: In order to acquire the three‐dimensional information (frequency, depth, and intensity) required for a range resolved Brillouin spectrum, either a multichannel or integration technique must be employed. This paper describes a system in which many laser shots are used to ’’build up’’ one Brillouin spectrum for each range gate in an ocean subsurface experiment.
TL;DR: In this paper, an extension of the Langevin method was used to calculate the fluctuations of a fluid about a stationary state held away from global thermal equilibrium by a temperature gradient or shear flow.
TL;DR: Using a triple-pass plane and a confocal Fabry-Pérot interferometers in tandem, a Brillouin spectrometer with a frequency resolution of 10(8) and a contrast of more than 10(10) is constructed.
Abstract: Using a triple‐pass plane and a confocal Fabry–Perot interferometers in tandem, we have constructed a Brillouin spectrometer with a frequency resolution of 108 and a contrast of more than 1010. Our system is controlled and fully stabilized by a desktop calculator, allowing efficient data collection for very long integration times.
TL;DR: In this paper, high-resolution angle-resolved photoemission spectra for Fe(100) are reported which identify and characterize surface states near the Fermi energy extending from the two-dimensional Brillouin zone.
Abstract: High-resolution angle-resolved photoemission spectra for Fe(100) are reported which identify and characterize surface states near the Fermi energy extending from $\overline{\ensuremath{\Gamma}}$ to $\overline{X}$ of the two-dimensional Brillouin zone. These results provide an experimental test of recent transition-metal surface electronic structure calculations and yield predictions relevant to spin-polarized photoemission from Fe(100).
TL;DR: In this paper, a formulation of the cluster approach to the electronic structure of solids is proposed, which allows exact matching of cluster eigenvalues to points in the Brillouin zone without interference by edge effects.
Abstract: A formulation of the cluster approach to the electronic structure of solids is proposed. This allows exact matching of cluster eigenvalues to points in the Brillouin zone without interference by edge effects. The scheme can be made self-consistent with respect to charge distribution.
TL;DR: In this article, the magnetic susceptibility of bismuth single crystals is measured in the trigonal-binary plane over a wide temperature range from 90 K to 540 K, and a function to express the observed values at any temperature is obtained by using a feast squares fitting method.
Abstract: The magnetic susceptibility of bismuth single crystals is measured in the trigonal-binary plane over a wide temperature range from 90 K to 540 K. Moreover, we get a function to express the observed values at any temperature, assuming that the temperature dependence of the energy gap dominates the susceptibility of bismuth. All coefficients of this function are determined by using a feast squares fitting method. Then we can evaluate the energy gap at any temperature; for example, the values of energy gaps at 0 K are 18 meV and 193 meV at the L-point and at the T-point in the Brillouin zone, respectively. They are nearly compatible with other experimental results.
TL;DR: In this paper, the first measurements of Brillouin frequency shifts and linewidths in a solid below 1 K were reported, where the resonant attenuation of 35-GHz phonons by two-level systems in vitreous silica and the related anomalous behavior of the velocity were observed down to 0.3 K, and the phonon energy was fully described by current theory based on the existence of two level systems in glasses.
Abstract: We report the first measurements of Brillouin frequency shifts and linewidths in a solid below 1 K. The resonant attenuation of 35-GHz phonons by two-level systems in vitreous silica and the related anomalous behavior of the velocity are observed down to 0.3 K, where the phonon energy $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\simeq}5kT$. The low-temperature data are fully described by current theory based on the existence of two-level systems in glasses. Above 10 K, in contrast, a qualitative agreement between theory and experiment is found.
TL;DR: In this article, the de Haas-van Alphen frequencies of the order of 10 4 gauss in LaB 6 have been studied in the low magnetic fields by the torque method.
Abstract: Angular variations of de Haas-van Alphen frequencies of the order of 10 4 gauss in LaB 6 have been studied in the low magnetic fields by the torque method. These frequencies are interpreted as interconnecting necks between nearly spherical ellipsoids which are centered at the points X in the simple cubic Brillouin zone. The magnetic breakdown field is estimated to be about 150 kOe from the Fermi surface parameter. These results are consistent with already reported do Haas-van Alphen data.
TL;DR: The Brillouin lines in the polarized light scattering spectrum of liquid CCI4, SiCl4 and SnCl4 were analyzed and relaxation times and relaxation strengths were calculated in the temperature range between the melting and the boiling points of these liquids.
Abstract: The Brillouin lines in the polarized light scattering spectrum of liquid CCI4, SiCl4 and SnCl4 were analysed and relaxation times and relaxation strengths were calculated in the temperature range between the melting and the boiling points of these liquids. The results were interpreted on the basis of an isolated binary collision model. The connection between experimental relaxation times, theoretical relaxation probabilities and molecular collision numbers as obtained from model considerations are discussed. The relative significance of factors as the anisotropy of intermolecular forces and multiple collision is assessed.
TL;DR: The backscattering of normally incident light by a medium in which there are two polariton branches is considered in this paper, and the boundary condition is written as u+ mu du/dz=0, and explicit results are given for this form.
Abstract: The backscattering of normally incident light by a medium in which there are two polariton branches is considered. The exciton boundary condition is written as u+ mu du/dz=0, and explicit results are given for this form. The phonon Green function which governs the scattering includes the reflection term which is of importance in opacity broadening. If the wavevector of the scattered light does not vary significantly over the linewidth, then the lineshapes are of the form derived by Dervisch and Loudon (1976); in general numerical evaluation is required. The opacity broadening means that the positions of the Brillouin peaks are shifted from those given by earlier theories. The equivalence between the differential formulation used here and an integrodifferential formulation is established and discussed.
TL;DR: In this article, complete tables of optical dipole selection rules for Bloch states in the hexagonal-close-packed lattice are given for symmetry lines and symmetry points in the Brillouin zone.
Abstract: Complete tables of optical dipole selection rules for Bloch states in the hexagonal-close-packed lattice are given for symmetry lines and symmetry points in the Brillouin zone. Included are both single and double group representations.
TL;DR: In this article, a linear dependence of the energies of E 1 + Δ 1 reflectivity maxima and of the shoulders connected with the E 0 + Δ 0 transitions for small manganese concentrations x was found.
TL;DR: In this article, the displacement gradients associated with transverse acoustic vibrations polarised parallel to the surface of a sample consisting of a plane parallel isotropic film deposited on an isotropically semi-infinite substrate are derived.
Abstract: Green functions are derived for the displacement gradients associated with transverse acoustic vibrations polarised parallel to the surface of a sample consisting of a plane parallel isotropic film deposited on an isotropic semi-infinite substrate. The frequency dependence of the corresponding Brillouin scattering cross section is calculated for arbitrary scattering angle. The spectrum includes contributions from the surface Love waves and from the higher-frequency bulk acoustic waves. Numerical calculations of Brillouin spectra are presented for a sample in which the substrate material is inactive in light scattering.
TL;DR: In this paper, a short-pulse (100 psec), 1.06-m laser backscatter from a high-pressure nitrogen gas target is reported, which shows the expected Brillouin red shift.
Abstract: Measurements are reported of short-pulse (100 psec), 1.06-..mu..m laser backscatter from a high-pressure nitrogen gas target. Spectral measurements clearly show the expected Brillouin red shift. The backscatter fraction saturated at approx. 40% at 2 x 10/sup 15/ W/cm/sup 2/ and what appears to be multiple Brillouin scattering in a long--gradient-length plasma is observed.
TL;DR: In this paper, a small polycrystalline ingot sample of NpCo2Si2 (weight ≈ 1.5 g) has been studied by neutron diffration between 2 and 160 K on the multi-detector D1B of ILL, Grenoble.
TL;DR: In this article, the Rayleigh-Brillouin spectra of He, Ne, and Ar were used to determine thermodynamic and transport properties of gases as a function of density and thus provide another method of probing intermolecular potentials.
Abstract: The Rayleigh-Brillouin spectra of He, Ne, and Ar are reported for the hydrodynamic region. The experiments show that light scattering may be used to determine thermodynamic and transport properties of gases as a function of density and thus provide another method of probing intermolecular potentials. In addition, the transition from the hydrodynamic to the kinetic regime is examined in terms of generalized hydrodynamics.
TL;DR: In this paper, room-temperature Brillouin-scattering measurements of the longitudinal and transverse sound velocities for the cubic crystals K2SnCl6, K2ReCl6 and K2SiF6 are presented.
Abstract: Room-temperature Brillouin-scattering measurements of the longitudinal and transverse sound velocities for the cubic crystals K2SnCl6, K2ReCl6, (NH4)2SnCl6 and (NH4)2SiF6 are presented. The elastic constantsc11,c12 andc44 are determined from the angular variation of the Brillouin line shifts. Furthermore, for K2SnCl6 the sound velocities in the [100]- and [111]-direction are investigated as a function of temperature, 256K≦T≦330K. A strong softening of thec11–c12 mode is observed in the para-distortive phase as the temperature approaches the phase transition temperatureTc1=262K from above, whilec44 shows no anomaly within the experimental error. These acoustic anomalies are interpreted theoretically by a mechanism based on the coupling of the elastic strain field to the fluctuations of the soft-mode coordinates.