表面增强拉曼散射概述（下）

表面增强拉曼散射概述（下）武建劳，郇宜贤，傅克德，张鹏翔（陕西师范大学物理系西安７１００６２）ＴｈｅＳｔａｔｕｓｏｆＳｕｒｆａｃｅ－ｅｎｈａｎｃｅｄＲａｍａｎＳｃａｔｔｅｒｉｎｇＷｕＪｉａｎｌａｏ；ＨｕａｎＹｉｘｉａｎ；ＦｕＫｅｄｅ；ＺｈａｎｇＰｅｎ...     

表面分形球、柱的光散射

分形和分维是近些年才兴起的一门处理复杂事物的新方法￣［１］。本文主要研究具有表面分形的球、柱的光散射特征。我们首先利用几何光学近似研究了一种表面满足自仿射原理的分形均匀球的散射，其散射特性与分维存在一定的关系。我们还利用微扰法讨论了表面具有沟槽的分形柱的光散射的分形特征。     

Electrochemical modulation spectroscopy

Applications of modulation spectroscopy techniques in electrochemical kinetic studies are reviewed. These methods permit direct in situ detection and identification of reaction intermediates and the measurement of kinetic rate constants approaching the diffusional limit. The results of spectral studies of adsorbed monolayers on metal surfaces are discussed with particular reference to surface roughness effects and photon-assisted charge-transfer transitions between the metal-adatom complex (considered to be a virtual bound state) and the conduction band of the substrate. Recent developments in the theory of the electroreflectance (ER) of metals are presented. The primary features are shown to arise from free-electron effects. At high positive biases, field-modulated interband transitions are enhanced owing to the reduced shielding of surface d orbitals. Surface plasmon generation in metals is also readily detected by ER measurements because of the ease with which interfacial optical parameters can be varied.     

Magnetic form factor determination by inelastic scattering of neutrons as compared to elastic scattering measures

The difference between the magnetic form factor for elastic and inelastic scattering of neutrons is derived to interpret recent neutron scattering experiment.     

Light scattering in a finite multi-particle system

We use the discrete dipole approximation (DDA) to perform electromagnetic scattering calculations of particles in a 3D volume. We adjust the spacing between the particles to change the volume densities of the scattering systems from approximately 10% to 100%. For very large volume densities, e.g. >50%, it is difficult to assign unambiguously whether the system is composed of a single heterogeneous particle or of multiple particles. Our calculations demonstrate optical effects attributable to multiple scattering in systems having volume densities as high as ～90%. This suggests that heterogeneities within naturally occurring particle systems can produce multiple-scattering effects. We also see evidence of very deep negative polarization branches (NPBs) (～?6%) that may have implications in interpreting polarization phase curves of cometary circumnuclear halos.     

Light scattering properties of a rough-ended optical fibre

Uniform wide-angle irradiation of a laser beam is achieved by roughening chemically the output end of an optical fibre. The angular distribution of the scattered light is analysed experimentally as a function of the incident angle of the laser beam into the input end of the fibre and the length of the rough core surface at its output end.     

Light modulation by a real stationary ultrasonic field

The temporal modulation of a light beam diffracted by a real stationary ultrasonic field in a liquid is studied. The stationary fields, experimentally obtained, are really ‘pseudo-stationary’, due to volume absorption and reflection losses.The modulation waveforms are analysed in a ‘thick-screen model’. The pseudo-stationary field has been considered as built up both by two antiparallel progressive beams of different amplitude, and by a stationary field plus a residual progressive beam. Different modulation formulae are obtained for beams either spatially superposed or placed at a finite distance.     

Pulse phase modulation as a method for timing measurements in Mössbauer spectroscopy

To study the time dependence of resonant scattering of gamma radiation in nuclear systems, and to determine the duration of interaction with them, it is proposed to set the reference time by phase-breaking in the incident wave.     

Light scattering from colloids

This paper presents a review of light scattering results on static and dynamic properties of ordered colloidal suspensions of charged polystyrene particles and fractal colloidal aggregates. Our studies on static structure factor,S(Q), of ordered monodisperse colloidal suspensions and binary mixtures of particles with different particle diameters, measured by angle-resolved Rayleigh scattering will be discussed. This will include determination of bulk modulus using gravitational compression and observation of colloidal glass (inferred from splitting of the second peak inS(Q)). Dynamic light scattering, with real time analysis of scattered intensity fluctuations, is used to get information about Brownian dynamics of the particles. Recent advances in the field of light scattering from colloidal aggregates which show fractal geometry will also be discussed.     

Light scattering in a fluid far from equilibrium

The integrated intensity is computed of each of the two Brillouin lines of a stationary fluid far from equilibrium in the presence of a temperature gradient. The difference in intensity found is due to mode-coupling effects and deviates appreciably from an extrapolation of earlier calculations near equilibrium.     

血液的光散射特性

测定了不同血液样品(全血、红细胞、血浆)在可见光的吸收光谱,研究了He-Ne激光经过全血和红细胞的偏振度的变化,得出了人体血液中对可见光的吸收和散射主要来自红细胞的结论.     

Photoassociative spectroscopy as a self-sufficient tool for the determination of the Cs triplet scattering length

In photoassociation spectroscopy, the line intensities of a given vibrational progression exhibit zero-signal modulation reflecting the node structure of the s-wave ground state wave function of two free colliding atoms. This leads to the determination of the scattering length. We performed photoassociation of cold Cs atoms polarized in the Zeeman sublevel f = 4, m(f) = 4. We analyzed the intensities of the lines associated with the Cs2 0(-)(g) state dissociating to the 6s(1/2)+6p(3/2) asymptote. This yields a value of the Cs triplet state scattering length, a(T) = -530a(0), while consistency requirements impose a value of the multipole ground state molecular coefficient, C6 = 6510 a.u.     

Infrared laser modulation spectroscopy

The lack of sensitivity in far infrared of conventional modulation techniques can be overcome by the use of a laser beam as a powerful high resolution infrared source. As an illustration of these features we describe a thermoreflectance experiment performed on mercury telluride using a frequency stabilised CO₂ laser. In this experiment a thin slab of HgTe was illuminated by the beam of the laser. A continuous shift of the Γ_6v?Γ_8c energy interval was produced by a slow temperature variation while the sample was submitted to a slight temperature modulation obtained by low frequency Joule heating. Synchronous and direct detection of the reflected beam gave the relative variation of reflectivity as a function of the sample temperature. Several spectra obtained at different emission lines enable us to determine the energy difference (E_g) between Γ_6v and Γ_8c inverted states. As a first approach a qualificative fit has been obtained with a simple model of dielectric constant and its temperature derivative. These results give the first direct determination of E_g near room temperature E_g = ? 117.04 meV at T = 286 ± 2 K.     

Light scattering from a fluid with a stationary temperature gradient

The spectrum of light scattered from a system in which a stationary temperature gradient is maintained is calculated on the basis of fluctuating hydrodynamics. Explicit expressions are obtained for the frequency dependence of the intensity of the modified Brillouin lines.     

Light scattering from a fluid with a stationary temperature gradient

The spectrum of light, scattered from a fluid with a stationary temperature gradient, is calculated on the basis of fluctuating hydrodynamics. Explicit expressions are obtained for the spectrum of the scattered light which is no longer symmetric around the frequency of the incident light. In particular the difference in height and intensity of the Brillouin lines is given. Furthermore the shift in the position of the maximum of the Rayleigh line is calculated.     

Light propagation and light scattering

A self-consistent theory is given for the propagation and scattering of light in a material medium. A generalized statement for the extinction theorem is obtained. To first order Yvon's result is recovered for the intensity of polarized scattered light.     

Light scattering by a finite obstacle and fano resonances

The conditions for observing Fano resonances at elastic light scattering by a single finite-size obstacle are discussed. General arguments are illustrated by consideration of the scattering by a small (relative to the incident light wavelength) spherical obstacle based upon the exact Mie solution of the diffraction problem. The most attention is paid to recently discovered anomalous scattering. An exactly solvable one-dimentional discrete model with nonlocal coupling for simulating diffraction in wave scattering in systems with reduced spatial dimensionality is also introduced and analyzed. Deep connections between the resonances in the continuous and discrete systems are revealed.