Absence of phase transformation of dense anthracene from Raman scattering

The high pressure vibrational properties of anthracene are investigated by using Raman scattering techniques in diamond anvil cells up to 7.1?GPa at room temperature. We present a detailed analysis of the normal vibrational modes of anthracene along with assignments of both symmetry and molecular motion. Our results demonstrate that almost all the modes shift toward higher frequencies and some peaks are broadened with increasing pressure. The smooth evolution of peaks corresponding to first and second nearest neighbor shell molecules with pressure rules out the possible existence of phase transformation. The mode Grüneisen parameters are obtained over the wide frequency range and relatively high pressure range.     

Dispersive phonon modes by resonant Raman scattering in AgBr

Dispersive Raman modes are observed in AgBr at low temperatures when the incident laser light is tuned across the indirect Γ-L^′₃ exciton absorption. These modes occur as sidebands of the resonantly enhanced 2 TO(L), TO+LA(L) and 2 LA(L) Raman peaks and are interpreted as being due to three- and four-phonon processes, respectively. They involve longitudinal acoustic phonons near the Brillouin zone center that exhibit strong dispersion. From analysing the spectra the relaxation of the intermediate exciton state can be studied in detail. The model applied enables us to obtain directly the average effective mass of the ls indirect exciton as 1.5 electron masses.     

Double resonance Raman scattering of second-order Raman modes from an individual graphite whisker

Resonant Raman scattering of second-order Raman modes from an individual graphite whisker synthesized by a high-temperature heat-treatment method at a special pressure was discussed here. The dependence of phonon frequencies on the incoming laser light and the frequency difference between Stokes and anti-Stokes scattering show their origin from double resonance Raman scattering. Our results show that all the experimental results of second-order Raman modes in graphite whiskers, such as the excitation-energy dependence on the mode frequency, the frequency shift between a second-order Raman mode and its fundamentals, and the frequency discrepancy between Stokes and anti-Stokes components of a second-order Raman mode can be well understood by double resonance Raman scattering.     

Raman scattering from plasmon-LO phonon coupled modes in ZnTe

Raman scattering spectra of LO phonon-plasmon coupled modes were observed at various temperatures below 400 K. The contributions of plasmon damping and phonon damping were analyzed by the use of the theoretical expression of the cross section and of Hall data. The temperature dependence of the calculated LO-phonon damping was discussed.     

用激光增益获取弱增益拉曼模式的受激拉曼散射光谱

当酒精的弱增益拉曼模式处于罗丹明640染料分子的激光增益范围时，在由悬垂液滴构成的圆形谐振腔中，观察到乙醇分子C—H伸缩系列模中多个弱增益拉曼模式的受激拉曼散射（SRS）光谱.随着抽运光的增强，迅速增长的强增益拉曼模式的受激辐射抑制了其他弱增益模式的SRS，并导致染料激光的完全淬灭.通过分析圆形腔腔模的光子速率方程和激光染料分子的三能级粒子数速率方程，解释了观察到的实验现象. 关键词： 受激拉曼散射 悬垂液滴 弱拉曼增益模式 激光增益     

Raman tensor elements for multiferroic BiFeO3 with rhombohedral R3c symmetry

A quantitative assessment of the Raman spectrum emitted from a coarse‐grained polycrystal of multiferroic BiFeO₃ has been carried out by means of a polarized Raman microprobe. The dependence of the intensity of Raman phonon modes has been first theoretically modeled as a function of crystal rotation. Then, the Raman tensor elements have been experimentally determined from the analysis of the A_g and E_g vibrational modes. Copyright © 2009 John Wiley & Sons, Ltd.     

Anomalous scattering data on some molten elements

In this work a method of analyzing anomalies in the pair distribution function of certain molten metals is suggested using the temperature dependence of experimental structure factor data.     

Double resonance in Raman scattering on single phonon modes of GaSe

Resonance in the Raman cross section for one-phonon modes of GaSe at 80°K has been observed for both incident and scattered photon energies equal to the direct exciton energy. The Raman efficiency spectrum within the region of resonance is shown to fit well with the shape computed from existing theories.     

Stimulated Raman scattering of lattice translational modes in liquid heavy water

A study was conducted on stimulated Raman scattering (SRS) when laser-induced plasma is formed in heavy water by focusing an intense picosecond pulsed Nd:YAG laser beam with wavelength 532 nm at room temperature. An unexpected 280 cm(-1) low frequency SRS line attributed to the lattice translational modes is observed. This SRS line and the internal-mode SRS lines indicate that the ice VII structure is formed in heavy water under the condition of laser-induced shockwave production.     

Raman study of some water modes in lithium sulphate monohydrate

The Raman spectrum of uncoupled OH stretching modes in lithium sulphate monohydrate has been determined and the line-widths of rotatory water modes have been measured in the range 90–290 K. These results provide evidence for the positions of the H atoms and a flipping motion of the water molecules respectively.     

Determination of the electro-optic contribution to the Raman scattering tensor of InPS4

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 1, pp. 147–150, January, 1990.     

Raman scattering from acoustic modes in Si/Ge superlattice waveguides

This paper discusses the design of acoustic vibrational modes in Si/Ge planar optical waveguides and its application in creating silicon-based Raman devices with a flexible spectrum. It addresses the deficiencies of the recently demonstrated Raman-based silicon lasers and amplifiers as they relate to spectral and low efficiency limitations of bulk silicon. The treatment is for in-plane scattering in a forward scattering configuration. In addition to calculating the spectrum and the efficiency for Raman active modes, it is shown that the negligible wave-vector of the phonons involved in this type of scattering allows for the use of the bandgap “pinching” effect to arrive at specific layer thicknesses for Si and Ge that optimize the scattering efficiency.     

Infrared absorption and Raman scattering on coupled plasmon-phonon modes in superlattices

We theoretically consider a superlattice formed by thin conducting layers spatially separated between insulating layers. The dispersion of two coupled phonon-plasmon modes of the system is analyzed by using the Maxwell equations, with the retardation effect included. Both transmission for the finite plate and the absorption for the semi-infinite superlattice in the infrared are calculated. Reflectance minima are determined by the longitudinal and transverse phonon frequencies in the insulating layers and by the density-state singularities of the coupled modes. We also evaluate the Raman cross section from the semi-infinite superlattice. The text was submitted by the authors in English.     

On the form of the Raman tensor of normal modes in electronically degenerate states

A theory is proposed to derive the form of the scattering tensor of normal modes of electronically degenerate states. Essentially group theoretical arguments are used and emphasis is placed on the origin of asymmetric tensors of Raman and Rayleigh processes.     

Raman tensor calculation for magnesium phthalocyanine

We present ab-initio density functional (DFT) calculations of the vibrational spectra of neutral magnesium phthalocyanine (MgPc) molecule and of its Raman scattering intensities.