Brillouin zone

About: Brillouin zone is a research topic. Over the lifetime, 13849 publications have been published within this topic receiving 383077 citations.

Coherent self-heterodyne detection of spontaneously Brillouin-scattered light waves in a single-mode fiber

Abstract: Time-domain reflectometry of spontaneous Brillouin scattering in a single-mode optical fiber is performed with a coherent self-heterodyne detection system containing a recently proposed external frequency translator and a single light-wave source. The light wave is divided into probe and reference light waves. The frequency of the probe light wave is upconverted by the translator by an amount approximately equal to the Brillouin frequency shift. The frequency-converted probe is launched into the fiber and spontaneously Brillouin scattered. As the frequency of the scattered probe is downconverted to near that of the reference light wave, coherent self-heterodyne detection of spontaneous Brillouin scattering becomes possible without having to use a fast-speed detector.

Structural and optical properties of paraelectric SrTiO3

Abstract: The electronic energy band structure, site- and angular-momentum-decomposed densities of states (DOS) and charge-density contours of perovskite SrTiO3 in the paraelectric cubic phase are calculated by the first-principles tight-binding linear muffin-tin orbitals method with atomic sphere approximation using density functional theory in its local density approximation. The calculated band structure shows a direct band gap of ~1.4 eV at the gamma point in the Brillouin zone. The total DOS is compared with experimental x-ray photoemission spectra. From the DOS analysis, as well as charge-density studies, we conclude that the bonding between Sr and TiO3 is mainly ionic and that the TiO3 entities bond covalently. Using the projected DOS and band structure we have analysed the interband contribution to the optical properties of SrTiO3 . The real and imaginary parts of the dielectric function and hence the optical constants (such as the reflectivity, refractive index, extinction coefficient and absorption coefficient) and the electron energy-loss spectrum are calculated. The calculated spectra are compared with the experimental results for SrTiO3 in the cubic phase and are found to be in good agreement with the experimental results in low-energy regions. The role of band-structure calculation as regards the optical properties of SrTiO3 is discussed.

AXIALLY SYMMETRIC MODEL FOR LATTICE DYNAMICS OF METALS WITH APPLICATION TO Cu, Al, AND ZrH$sub 2$

Abstract: A lattice dynamics model (A-S model) is proposed for metals which assumes that the restoring forces between the ions have the character of bond stretching and axially symmetric bond bending. It is shown that this type of restoring force is derivable from a sum of spherically symmetrical two-body potentials, $v({R}_{\mathrm{ij}})$, taken over all ($i, j$) pairs of lattice sites separated by a distance ${R}_{\mathrm{ij}}$. The dynamical matrix for a face-centered cubic lattice is worked out for the first three neighbor shells of atoms. The dispersion curves for aluminum and copper are derived from the elastic constant and thermal diffuse x-ray data. The A-S force constants or Cu and Al fall off rapidly with distance and give dispersion curves which are at least as good as those derived from the third-neighbor general tensor force model. Particularly noteworthy is the fact that Walker's tensor force constants for Al are nearly axially symmetric. However, Jacobsen's tensor force constants for Cu are not axially symmetric. Contrary to this observation, it is found that White's force constants derived by using Feynman's theorem are nearly axially symmetric.The A-S model is also applied to Zr${\mathrm{H}}_{2}$ which has a tetragonally deformed fluorite structure. It is shown that the six optical branches are flat to within 3% over the entire Brillouin zone and that the hydrogen-hydrogen interactions are very weak compared to the hydrogen-zirconium interactions. The dynamical matrix for the acoustic spectrum is derived.

Dynamic stabilization of cubic Ca Si O 3 perovskite at high temperatures and pressures from ab initio molecular dynamics

Abstract: The stability of cubic $\mathrm{Ca}\mathrm{Si}{\mathrm{O}}_{3}$ perovskite (CaPv) at high temperatures and pressures is investigated by vibrational normal-mode analysis. We compute power spectra of mode autocorrelation functions using a recently developed hybrid approach combining ab initio molecular dynamics with lattice dynamics. These power spectra, together with the probability distributions of atomic displacements, indicate that cubic CaPv is stabilized at $T\ensuremath{\sim}600$ K and $P\ensuremath{\sim}$ 26 GPa. We then utilize the concept of phonon quasiparticles to characterize the vibrational properties of cubic CaPv at high temperature and obtain anharmonic phonon dispersions through the whole Brillouin zone. Such temperature-dependent phonon dispersions pave the way for more accurate calculations of free-energy, thermodynamic, and thermoelastic properties of cubic CaPv at Earth's lower mantle conditions.

One-End-Access High-Speed Distributed Strain Measurement with 13-mm Spatial Resolution Based on Brillouin Optical Correlation-Domain Reflectometry

Abstract: We demonstrate a one-end-access high-speed distributed strain sensing with high spatial resolution in optical fibers based on Brillouin optical correlation-domain reflectometry. In this work, Brillouin frequency shifts (BFSs) of a 3- cm fiber section are measured with 13- mm spatial resolution and 50- Hz sampling rate. To our knowledge, this spatial resolution is the best result ever reported in Brillouin scattering-based reflectometers, and is superior to that obtained in Brillouin optical time-domain analyzers, though the signal-to-noise ratio is deteriorated. Data processing to find the peak in the Brillouin spectrum is newly introduced to show directly the BFS with a sampling rate of 19 Hz, and the measurement of vibrated strains at frequencies of up to 4 Hz is presented under 22- cm resolution.