Study of the elastic stiffness constants of thiourea by Brillouin scattering

All the elastic stiffness constants of thiourea have been measured at room temperature. The value of C₆₆(0.7 × 10¹⁰dynes/cm²) is very low. The C₁₁ and C₃₃ constants exhibit discontinuities at 169 and 202 K. The longitudinal acoustic phonons propagating in the c direction are very strongly damped in the vicinity of 202 K.     

水中受激布里渊散射阈值的研究

在对水中受激布里渊散射阈值的研究中,针对传统定义上的不足,提出一种新的定义和新的测量方法.测量了不同能量的光束在不同长度的水介质中传输,在宽线宽和窄线宽情况下水的衰减系数.通过水的衰减系数的变化来确定不同情况下受激布里渊散射的阈值.试验发现,水中的受激布里渊阈值在理想稳态和理想瞬态下是一个常数,只与泵浦激光和介质属性有关,和介质长度无关;在中间情况下,受激布里渊阈值是否与介质长度有关,还要根据具体情况来分析.     

Brillouin scattering study of multilayer cobalt-niobium films

Spin waves which are characteristic of periodic structures of thin ferromagnetic Co films alternating with nonmagnetic Nb films have been investigated by means of Brillouin light scattering. The dependence of the magnon frequencies on the magnetic inplane field and on the wave-vector was measured for several samples with different numbers and thicknesses of the layers. The experimental data are in good agreement with a theory of magnetostatic surface spin waves in such media elaborated by Grünberg and Mika. The amplitudes of the transverse magnetization in the different layers of the stack have been calculated. The highest frequency branch resembles the Damon-Eshbach surface magnon. With decreasing frequency the branches acquire volume mode character. In addition, a number of phonon branches has been observed which are interpreted as plate modes of the combined Co-Nb layer on the Si substrate.     

钽铌酸锂晶体的布里渊散射研究

研究了钽铌酸锂(LiTa_xNb_(1-x)O_3,x=0.0013,0.0052,0.015,0.06)晶体在室温的布里渊散射.给出了它们的弹性刚度常数和压电应力常数.测量了一种组份晶体的布里渊散射频移在50K～580K范围内的温度特性.发现某些声子散射谱中除三个正常峰外还存在一个异常峰.     

Brillouin scattering study of methanol at high pressure

Abstract

Brillouin scattering has been used to study methanol as a function of pressure up to 8.4 GPa. Our near-forward-scattering experiments yield the pressure dependence of the velocity of longitudinal acoustic (LA) phonons, while we determine the pressure dependence of the product of the index of refraction and the LA phonon velocity from our backscattering experiments. The pressure dependence of the LA phonon lifetimes is obtained from the linewidth of the measured Brillouin peaks. From our backscattering experiments we find that the normalized phonon attenuation is a decreasing function of pressure.     

Brillouin scattering study of the orientationally disordered phase of cyclohexanol

Brillouin scattering was used to measure the velocity and attenuation of longitudinal hypersonic waves in the orientationally disordered (OD) phase of a cyclohexanol single crystal and at the OD-liquid transition. Our results show that the coupling with a high-frequency relaxation mechanism, which dominates the behaviour of the hypersonic waves in the liquid, is still efficient in the OD phase.     

Brillouin scattering study on the wave properties in thin SiC films

The modified Rayleigh wave velocities on the SiC hetero-epitaxial films have been investigated using a Brillouin scattering technique. The SiC nanoscopic films were formed on clean surface of Si substrates by the molecular ion beam technique or Ion beam induced chemical vapor deposition. Back scattering geometry was used to obtain the ripple Brillouin scattering from the film surface. Owing to the high stability of the measurement system, the precise velocity measurement was performed. As a result, Rayleigh wave velocity showed a clear dependence on the crystalline structure of SiC film, indicating that the shear moduli of very thin epitaxial films shows similar tendency with those of SiC bulk sample.     

Inelastic neutron scattering study of commensurate-incommensurate phase transition in thiourea

This paper presents a study of the nature of the incommensurate lattice instability in deuterated thiourea by inelastic neutron scattering. It shows clearly a “soft mode” which condenses at the phase transition in a satellite reflexion. A study of related dispersion curves along the [O ξ O] direction shows an unusual spectral shape in a large temperature range above T_c.     

Brillouin scattering and the CMB

Brillouin scattering of photons off the density fluctuations in a fluid is potentially important for cosmology. We derive the Brillouin spectral distortion of blackbody radiation, and discuss the possible implications for the cosmic microwave background. The thermal Sunyaev-Zeldovich effect is slightly modified by Brillouin distortion, but only at very long wavelengths.     

Brillouin scattering study of epoxy adhesive layers during cure

The isothermal curing process of thin epoxy adhesive layers (mixture of a bisphenol A-based epoxy prepolymer and an aliphatic diamine curing agent) has been investigated. The Brillouin scattering technique with 90 degrees A scattering geometry enables simultaneous measurements of longitudinal and shear wave properties in the GHz range. Observed longitudinal and shear wave velocities showed similar changes during cure. They rapidly increased and gradually became constant, reflecting the elastic changes of the epoxy layer. The final velocities, however, clearly depended on the curing temperature. Taking the glass transition process of epoxy resins into consideration, these curing behaviors in thin layers are discussed.     

Brillouin scattering in layered structures

Theoretical and experimental results on Brillouin scattering in inhomogeneous materials are presented: Normal elastic modes and Brillouin intensities have been calculated for a periodic layer system. Measurements on semicrystalline polybutene-1 are discussed in terms of the theoretical results. Both theory and experiment yield several Brillouin lines in VV scattering instead of the one peak characteristic for homogeneous specimens.     

Brillouin scattering in the layer compound GaSe

Brillouin scattering has been used to obtain the five independent elastic constants in the layer compound GaSe. The results show clear elastic anisotropy of the crystal. Resonant Brillouin scattering near the absorption edge has also been studied, but no resonant enhancement was found.     

Brillouin scattering study of phase transitions in T1Ins2

The temperature dependence of the elastic coefficients of T1InS₂ has been investigated by Brillouin scattering measurements. For longitudinal phonons propagating in the (001) plane the variation of ΔC_∼∼(T_c−T) was found below the ferroelectric transition point (T_c=189 K). For propagation perpendicular to the (001) plane (C₃₃ mode) clear anomalies were observed at T=213 K and T=195 K. Between these temperatures the Brillouin peaks show broadening, which is attibuted to a coupling between the acoustic mode and an overdamped mode.     

KrF激光受激布里渊散射反射率稳定性的研究

实验研究发现抽运功率密度（或抽运能量）的波动引起的受激布里渊散射(SBS)反射率的不稳定程度受实验参数（抽运能量、介质气压和透镜焦距）的影响.当抽运能量、介质气压和透镜焦距这三个参数同时满足下列条件时可以获得稳定的输出：抽运能量超过5倍的SBS阈值，介质气压在16×105Pa和透镜焦距在15—50cm的范围内；同时还发现当改变实验参数时SBS反射率与稳定性的变化规律完全一致，反射率越高稳定性越好.通过理论分析得到 SBS反射率的相对稳定度实际上是受GIL因子的影响，理论计算与实验符合得很好. 关键词： KrF激光 受激布里渊散射 反射率 稳定度     

Brillouin scattering in microstructures involving GaAs

Light interaction with Rayleigh Surface Waves propagating parallel to the surface of GaAs substrates implanted with heavy ions has been used for the determination of the acoustic velocity in amorphous GaAs. A complete analysis of the peak-width of the scattered light from folded acoustic modes, including the contribution of the phonon lifetime and the light absorption, is presented for superlattices. In the case of the GaAs-AlAs systems, this analysis can explain the sharpness of the observed peaks.     

Brillouin scattering in cubic potassium cyanide

The temperature dependence of the elastic shear constant C₄₄ of cubic potassium cyanide has been measured by optical Brillouin spectroscopy in the temperature range from 300-168 K. A strong softening of the constant C₄₄ was found in agreement with the results of ultrasonic and neutron measurements.     

后向受激布里渊散射诱导的光学材料破坏机理研究

 区别于传统的受激布里渊散射(SBS)发生器和放大器，提出了一种新型的SBS模型：自供种子光模型 (self Stokes seeding，SSS)。数值求解了SBS耦合波方程组，得到了SBS诱导应力的时空分布。基于SSS建立了高功率激光辐照下光学材料破坏阈值的计算模型，研究了SBS破坏阈值与激光脉宽以及作用区长度的关系。研究发现，SBS作为一种破坏机制，表现为前表面破坏，且破坏阈值与激光脉宽以及作用区长度均成反比。     

On the material response in stimulated Brillouin scattering

We re-examine behavior of the material response in stimulated Brillouin scattering and from this revise its theoretical formalism. We show that the response out of exact Brillouin resonance splits into two processes: one is the induction of a moving density grating, propagation characteristics of which follow these of the beat pattern of pump and Stokes fields, and the other is the induction of an acoustic wave, frequency of which coincides with that of the beat pattern but which propagates at the acoustic velocity in the medium. The resulting equations for the response amplitudes are solved analytically in several representative cases.     

Brillouin scattering study of elastic properties related to polymorphism in 2-chloronaphthalene

The frequency and line width of the longitudinal acoustic mode propagating in the (010) direction of 2-chloronaphthalene have been measured by Brillouin scattering, from 8 to 326 K. Measurements of the transverse mode frequency between 200 and 326 K are also given. While the standard variation due to anharmonic phonon-phonon interactions is observed up to 200 K, a large increase of the sound absorption and the related decrease in the velocity appear in the vicinity of the phase transition. This behaviour can be explained by a coupling between the strain components and the order parameter. The form of this coupling is discussed for the two acoustic modes.