Li+ neutralization as a probe of the local electronic potential in Li+-alkali covered metal surface collisions

A theoretical study of Li⁺ neutralization by collision on an alkali covered Al surface is presented. The neutralization probability is computed for Li atoms back scattered from Al sites and from alkali sites on the surface. The calculations are performed with a model representation using lithium as a representative for alkali adsorption. The results reproduce the very large difference in neutralization probability for Li scattered from substrate and adsorbate sites experimentally observed by Weare and Yarmoff [Surf. Sci. 348 (1996) 359] and thus confirm the importance of local effects in atom-surface charge transfer. For scattering from adsorbate sites, the neutralization is shown to be associated with a very large excitation probability of the scattered Li atom.     

Simulation of light scattering by a particle on a film-coated substrate using coupled-dipole method

The intensity of light scattered by a submicron particle on a film-coated semiconductor substrate is calculated as a function of the thickness of the film using the coupled-dipole method. The result of calculation reproduces the experimentally observed features, i.e., the oscillatory dependence of the scattering intensity on the thickness and the enhancement of the scattering intensity for very thin films. The enhancement is reproduced only when the dipole-dipole interaction between the particle and the substrate is included in the calculation. Using the method we propose, the scattering intensity can be calculated for an arbitrary size and shape of particle on an arbitrary thickness of film.     

Signatures of electromagnetic surface-shape resonances in scattering of pulsed beams from surface defects

We predict theoretically that electromagnetic resonances supported by surface defects can be detected experimentally by study of the scattering of electromagnetic pulses from these defects, and we formulate the optimal conditions for such experiments. Numerical scattering simulations confirm that the proposed scattering probes unambiguously identify resonance signatures. The approach that we suggest proves to be superior to conventional analysis of features in the dependence of the far-field intensity of scattered monochromatic light on its frequency, since these features do not necessarily point at resonant frequencies.     

Influence of surface roughness on the elastic-light scattering patterns of micron-sized aerosol particles

The relation between the surface roughness of aerosol particles and the appearance of island-like features in their angle-resolved elastic-light scattering patterns is investigated both experimentally and with numerical simulation. Elastic scattering patterns of polystyrene spheres, Bacillus subtilis spores and cells, and NaCl crystals are measured and statistical properties of the island-like intensity features in their patterns are presented. The island-like features for each class of particle are found to be similar; however, principal-component analysis applied to extracted features is able to differentiate between some of the particle classes. Numerically calculated scattering patterns of Chebyshev particles and aggregates of spheres are analyzed and show qualitative agreement with experimental results.     

Modulation of optical pulses under electromagnetically induced transparency conditions: transfer of the Rabi oscillations manifestation from the radiofrequency to the optical range

The relative intensities of lines in resonance Raman scattering spectra of isolated skatole and skatole-water complex have been calculated quantum mechanically. The influence of the intermolecular interaction on these spectra has been considered. Particular features of the intensity distribution in the resonance Raman scattering spectra of indole and skatole have been compared.     

均匀椭球粒子对拉盖尔-高斯光束的散射特性研究

基于广义Mie理论, 研究了椭球粒子对在轴入射的拉盖尔-高斯光束的散射特性. 通过局域近似法求解椭球坐标系中的波束因子, 计算得到了波束因子之间满足的普遍关系. 对散射强度随椭球粒子不同尺寸参数和扁圆程度的变化特性进行了数值计算, 并针对不同拓扑荷时的散射强度进行了对比分析. 结果表明: 当椭球粒子尺寸在与入射光波长可比拟的范围内变化时, 散射强度随尺寸参数的增大而增大, 随椭球长短轴之比和拓扑荷的增大而减小. 本文的理论研究能够为拉盖尔-高斯光束在粒径测量、大气激光通信、 大气遥感等领域的应用提供更准确的粒子模型和参考价值. 关键词： 椭球粒子 拉盖尔-高斯光束 波束因子 散射强度     

The special features of the ground state in CeAl3

The temperature (3–60 K) and transferred momentum (0.3–2.3 Å^?1) dependences of the intensity of quasi-elastic magnetic neutron scattering were studied for the polycrystalline heavy-fermion CeAl₃ compound to elucidate the special features of its ground state. Transferred momentum variations caused oscillations of the intensity of quasi-elastic magnetic neutron scattering, which was evidence of magnetic correlations in the f-electron subsystem occurring in a fairly wide temperature range.     

Investigation of micropipes in 6H-SiC by Raman scattering

The spectra of 6H-SiC crystals including micropipes have been examined for the Si face using Raman scattering. The first-order Raman features reveal that the intensity of the transverse optical phonon band centered at ∼796 cm⁻¹ is sensitive to the micropipes. And the second-order Raman features of the micropipes in bulk 6H-SiC are well-defined using the selection rules for second-order scattering in wurtzite structure. It is found that there are some second-order peaks missing for the micropipe-including sample, which may be induced by the reduction of the incident laser intensity at around the micropipe, especially the uneven surface in the inner wall of the micropipe. These features might also be employed to characterize other structural defects such as screw-dislocations and threading edge dislocations.     

Impurity-induced states on the surface of a three-dimensional Weyl semimetal

We study theoretically the features of impurity-induced states on the surface of a three-dimensional Weyl semimetal in this work. For calculating the impurity-induced local density of states based on T-matrix formulation, we found that for different Weyl semimetal phases the behaviors of a local impurity exhibit distinguishable prominent features for the surface Fermi arc states. Due to two opposite-directional and -chirality surface currents for a surface, a bound state appears at the unitary limit of scattering intensity near the impurity site. Then the resonance condition for different Weyl semimetal phases and scattering intensity is investigated. Our results can be used to identify distinctive topological phases of Weyl semimetal. Furthermore, the relevance of topological nodal-point and -line systems is discussed. Some relation between our theoretical results and current experimental scheme are also discussed.     

Scattering of light and neutrons in a model for superionic conductors

We discuss the cross sections for neutron scattering and light scattering from a superionic conductor. The motion of the mobile ions is treated as an independent continuous diffusion process through a periodic potential. While this determines the neutron scattering intensity completely, the light scattering is, in addition, strongly influenced by the spatial variation of the polarizability. This leads to selection rules and to differences between the two kinds of spectra. We present a rather complete study of a one-dimensional model which displays the general features of the problem. The results are based on a numerically accurate solution of the corresponding Fokker-Planck equation.     

Influence of dynamic effects in nuclear resonant Bragg scattering on the accuracy of determination of self-diffusion coefficient in 56Fe/57Fe periodic multilayers

The angular dependences of nuclear resonant scattering are considerably different from respective X-ray reflectometry curves because of some special features of their detection and nuclear decay acceleration (speedup effect) in the conditions of coherent scattering. Model calculations show that the kinematic formula relating the intensity of the nuclear Bragg reflection maximum at different stages of annealing to the diffusion coefficient is inapplicable when the Bragg peak falls near the critical angle.     

Optical backscattering measurements from fractal surfaces and their possible relevance to radar scattering from the sea surface

In spite of recent progress, existing theories of electromagnetic wave scattering by rough surfaces cannot yet explain several important features of microwave sea echo, particularly in grazing incidence geometries. To explain them it is necessary to develop scattering models that can reproduce the features in a robust way. The aim of this paper is to report laboratory optical frequency experiments designed to aid achievement of this objective. In particular, polarization sensitive measurements of the backscattered intensity are reported for a range of characterized fractal surfaces using visible laser radiation. The appearance of enhanced backscattering peaks are observed even quite close to grazing incidence for some types of surfaces and indicate the importance of multiple scattering. It is also shown that the dependence of the backscattering cross-section on incidence angle bears some gross similarities to that obtained from microwave scattering from the sea surface for high index fractal surfaces that exhibit intermittency.     

基于偏振门的动态光散射颗粒测量法的研究

为了解决动态光散射纳米颗粒测量技术无法测量高浓度颗粒粒径的难题,提出了一种基于偏振门的动态光散射测量法。从动态光散射和Mie理论出发,理论分析了在高浓度溶液下多重散射效应对散射光偏振态和颗粒粒度测量结果的影响。根据散射光偏振特点,结合偏振门检测技术,改进了传统的动态光散射光学系统。实验研究了在低浓度和高浓度溶液时,不同偏振角度下的散射光强和粒度测量值,完善了散射光的偏振理论。采用90°偏振门检偏,通过各种浓度下的实验,证明了方法的可行性。该方法较之目前同类方法具有原理和结构简单,系统易于维护的特点。     

Hypothesis of the spatial adjustment of optical inhomogeneities of water and its confirmation through experiments on measurements of light scattering

To explain the features of the scattering and propagation of light in liquid water, a hypothesis of the spatial adjustment of global optical inhomogeneities of water has been proposed. An analytical expression for the intensity of light singly scattered on randomly distributed clusters filling the entire water bulk has been obtained in the Rayleigh-Gans approximation. It has been shown that theoretical estimates are in good agreement with the experimental data on the volume scattering function in pure filtered water.     

Observation of a metastable periodic structure for the (001) surface of KTaO3 after cleaving in situ

Helium atom diffraction experiments carried out under ultrahigh vacuum conditions on a freshly cleaved (001) surface of KTaO3 reveal metastable features which decay over a period of several hours. The initial He diffraction pattern contains large scattering intensity satellite peaks very close to the specular reflection beam. As time from cleaving elapses, the satellite intensities diminish virtually to zero while the specular intensity increases, and the diffraction pattern evolves into one consistent with the (1x1) bulk termination surface. The data are compared with model calculations for scattering from a series of terraces at two heights with a distribution of terrace lengths [Surf. Sci. 384, 15 (1997)].     

红外区磷化稼散射强度的计算与分析

根据Mie散射理论,对磷化稼粒子光散射特性进行了数值计算与理论分析,得到了散射强度与散射角、入射波长以及偏振度与散射角的关系。研究表明,红外波段光散射很小,前向散射占有优势,粒子半径越大,前向散射越强,并且在散射角900方向上能观测到线偏振光,对研究GaP红外光学特性提供了理论参考。     

Multiple time scales in diffraction measurements of diffusive surface relaxation

We grew SrTiO3 on SrTiO3(001) by pulsed laser deposition, using x-ray scattering to monitor the growth in real time. The time-resolved small-angle scattering exhibits a well-defined length scale associated with the spacing between unit-cell high surface features. This length scale imposes a discrete spectrum of Fourier components and rate constants upon the diffusion equation solution, evident in multiple exponential relaxation of the "anti-Bragg" diffracted intensity. An Arrhenius analysis of measured rate constants confirms that they originate from a single activation energy.     

上海激光电子γ源

激光具有高强度、 高极化度等优异的性能。 用激光束轰击高能电子束就可以产生高强度、 高极化度的γ射线束。 上海激光电子γ源就是上海同步辐射装置上的这样一条束线站。 预计可以获得能量范围为1—22 MeV的准单色、 高强度（109—1011 s-1）和高极化度（线极化或圆极化）的γ射线束。 介绍了这条束线站目前的进展情况。 Shanghai Laser Electron Gamma Source (SLEGS) is a high intensity,short pulse and compact γ ray source which is based on inverse Compton scattering via interaction between pulsed high power laser beams and picosecond relativistic electron bunches. One of the attractive features of the laser Compton scattering is the easy control of polarization of the produced high energy photons that duplicates polarization of the applied laser beam. The γ ray with energy up to 22 MeV and intensity of 109—1011s 1 are expected to be produced by Compton backscattering of CO2 laser photons on the 3.5 GeV electrons bunches in the Shanghai Synchrotron Radiation Facility (SSRF). In this communication, we report same simulation results and the progressing status of SLEGS.     

Enhanced Raman scattering from nano-SnO2 grains

We present the Raman spectra of nano-SnO_{2} grains with sizes from 4nm to 80nm excited by 532nm and 1.06μm lines. The enhanced Raman scattering of the nanograins is observed for both exciting lines when the grain size is less than 8nm. The less the grain size is, the more intensely the Raman scattering is enhanced. According to our results, the enhancements of the Raman intensity are a few tenfolds and different for different exciting lines when the grain size is 4nm. It can be attributed to enhanced Raman scattering by electron－hole pair excitations in the nanograins that originate from sub-microscopic (10nm) size and other defect- and surface-related features. A critical size that divides respective predominance of bulk properties and the defect-, surface-, and size-related features can be determined to be about 8nm.