Coherent light scattering from a two-dimensional Mott insulator

We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak parameters by a simple analytic model. In contrast to Bragg scattering, scattering from a single plane yields diffraction peaks for any incidence angle. We demonstrate the feasibility of detecting spin correlations via light scattering by artificially creating a one-dimensional antiferromagnetic order as a density wave and observing the appearance of additional diffraction peaks.     

Low-frequency inelastic light scattering from As-S glasses

Raman scattering from As-S glasses were observed in the low-frequency region, from 5 to 60 cm^?1. The spectral features depend on the quenching and annealing conditions as well as on the temperature and the composition. The spectrum was explained in terms of the vibration of the layer-like clusters coupled with each other through van der Waals forces.     

Theory of inelastic scattering from magnetic impurities

We use the numerical renormalization group method to calculate the single-particle matrix elements T of the many-body T matrix of the conduction electrons scattered by a magnetic impurity at T=0 temperature. Since T determines both the total and the elastic, spin-diagonal scattering cross sections, we are able to compute the full energy, spin, and magnetic field dependence of the inelastic scattering cross section sigma(inel)(omega). We find an almost linear frequency dependence of sigma(inel)(omega) below the Kondo temperature T(K), which crosses over to a omega(2) behavior only at extremely low energies. Our method can be generalized to other quantum impurity models.     

X-ray inelastic scattering from small particles of graphite

The spectrum of inelastically scattered X-ray radiation from small particles of graphite shows energy losses which are due to volume and surface plasmons, as in the foil case. Surface plasmons from spherical particles (SPS) have not been observed. It is shown that graphite is inappropriate in the study of SPS using X-ray scattering experiments.     

Stimulated light emission and inelastic scattering by a classical linear system of rotating particles

The rotational dynamics of particles subject to external illumination is found to produce light amplification and inelastic scattering at high rotation velocities. Light emission at frequencies shifted with respect to the incident light by twice the rotation frequency dominates over elastic scattering within a wide range of light and rotation frequencies. Remarkably, net amplification of the incident light is produced in this classical linear system via stimulated emission. Large optically induced acceleration rates are predicted in vacuum accompanied by moderate heating of the particle, thus supporting the possibility of observing these effects under extreme rotation conditions.     

Many-photon effects in inelastic light scattering

The usual approach to second harmonic generation (SHG) is based on low-order pertubation theory and neglects the changes in the electronic states that are induced by the exciting beam. To see whathappens in this approximation fails we propose a new formalism, based on the method of excitation amplitudes, to set up a theory of the SHG response and other inelastic light scattering phenomena. We develop the quantum theory in the dipole approximation and show that the inclusion of electron-photon coupling to all others leads to new features. Strong exciting fields produce a nonnegligible SHG response in highly polarisable centro-symmetric systems, and the emitted spectrum shows a dynamical Stark effect.     

Coherent soft X-ray magnetic scattering

X-ray sources are exceptional tools for studying the structure of matter down to atomic-length scales, but across a wide range of fields there are samples that have remained notoriously difficult to study, such as airborne particles, particles in solution, membrane proteins, and macromolecular complexes. The advancement of imaging techniques to address these elusive samples has been a big motivation for constructing new X-ray light sources. Fourth-generation light sources, commonly called X-ray free-electron lasers (XFELs) [1 Madey, J. 1971. Journal of Applied Physics, 42: 1906–1913. [Crossref], [Web of Science ®] , [Google Scholar]], represent a huge step forward, with upwards of nine orders of magnitude increase in peak brightness for hard X-rays. As of 2012, four such XFELs are already productively operational (in Germany [2 Ackermann, W. 2007. Nature Photonics, 1: 336–342. [Crossref], [Web of Science ®] , [Google Scholar]], the U.S. [3 Emma, P. 2010. Nature Photonics, 4: 641–647. [Crossref], [Web of Science ®] , [Google Scholar]], Japan [4 Ishikawa, T. 2012. Nature Photonics, 6: 540–544. [Crossref], [Web of Science ®] , [Google Scholar]], and Italy [5 Allaria, E. 2012. Nature Photonics, 6: 699–704. [Crossref], [Web of Science ®] , [Google Scholar]]), with at least five more planned for the next 10 years. These lasers produce femtosecond pulses of extremely intense coherent radiation through the positive feedback between a co-moving electron bunch and the radiation it emits when they traverse an extended undulator. This process creates remarkably strong, tunable probes that will undoubtedly change the way we examine nanoscale structure and dynamics.     

Coherent light scattering from ruby dressed with rf photons

We observed a new kind of coherent light scattering from ruby subjected to an rf Stark field and explained it in terms of rf photon dressing. The theory is also applied to explain the sublevel coherence generation by an rf Stark field in the coherent Raman beat spectroscopy.     

Angle-resolved second-harmonic light scattering from colloidal particles

We report angle-resolved second-harmonic generation (SHG) measurements from suspensions of centrosymmetric micron-size polystyrene spheres with surface-adsorbed dye (malachite green). The second-harmonic scattering profiles differ qualitatively from linear light scattering profiles of the same particles. We investigated these radiation patterns using several polarization configurations and particle diameters. We introduce a simple Rayleigh-Gans-Debye model to account for the SHG scattering anisotropy. The model compares favorably with our experimental data. Our measurements suggest scattering anisotropy may be used to isolate particle nonlinear optics from other bulk nonlinear optical effects in suspension.     

微小颗粒的光散射数值模拟

简单介绍了以经典Mie理论为基础的光散射测量技术在颗粒直径和颗粒浓度测量中广泛的应用。分别以Mie理论和离散偶极子近似理论(DDA)为基础, 用数值计算方法分析了球型颗粒的光散射特性，给出了微小颗粒对平行入射光散射的强度函数和散射偏振度的数值计算方法。得到了强度函数和偏振度随相关物理参量变化的三维图，为微小颗粒散射研究提供了一种三维视图。计算结果表明：当尺度参量x＜4时，2种方法所得结果差异不大；随尺度参量增大，2种方法所得结果出现较大差异。与经典Mie理论相比，由于离散偶极子近似理论可以解决各种形状的颗粒散射问题，其应用前景更广泛。     

Theory of light scattering from a system of interacting Brownian particles

Starting from a N-particle diffusion equation for a system of N interacting spherical Brownian particles, a non-linear transport equation for concentration fluctuations δc(r, t) of the particles is derived. This dynamic equation is transformed into a hierarchy of equations for retarded propagators of increasing numbers of concentration fluctuations. A cluster expansion to lowest order in the average concentration results in a set of two coupled equations. The spectrum of light scattered by the interacting particles is in general not a Lorentzian, due to the non-linear term in the transport equation. For small scattering wave vectors k the width is D(ω)k², where ω is the transferred frequency. It is shown that D(0) = D_e, the effective diffusion coefficient. For a hardcore interaction potential the spectrum is Lorentzian and it is found that D_e = D₀(1 + φ), where D₀ is the diffusion constant for independent particles and φ the volume concentration of Brownian particles.     

Deep inelastic electron scattering on light nuclei

Czechoslovak Journal of Physics -     

Coherent inelastic backscattering of intense laser light by cold atoms

We present a nonperturbative treatment of coherent backscattering of intense laser light from cold atoms and predict a nonvanishing backscattering signal even at very large intensities, due to the constructive (self-)interference of inelastically scattered photons.     

A unified model for diffractive and inelastic scattering of a light atom from a solid surface

A simple model for gas-surface scattering is presented which permits treatment of inelastic effects in diffractive systems. This model, founded on an impulsive collision assumption, leads to an intensity distribution which is just a sum of contributions from n-phonon scattering events. Furthermore, by using a convenient form for the repulsive interaction potential, analytic expressions are obtained for the elastic and one-phonon intensities that are in qualitative agreement with experimental results.     

Extraction of cross-sections of inelastic scattering from energy spectra of reflected atomic particles

REELS spectra of the electrons reflected off niobium are measured with energy resolution <0.5 eV within the 5–40 eV energy range of the probing beam. The measurements were performed for the scattering angles θ = 45° and θ = 120° by means of two electron guns. The process of energy losses is described within the framework of a model with three different energy loss laws: surface, intermediate, and bulk layers are considered. Differential cross-sections of inelastic scattering are represented in the form of simple equations.     

Coherent light scattering from semicontinuous silver nanoshells near the percolation threshold

We report on measurements of visible extinction spectra of semicontinuous silver nanoshells grown on colloidal silica spheres. We find that thin, fractal shells below the percolation threshold exhibit geometrically tunable plasmon resonances. A modified scaling theory approach is used to model the dielectric response of such shells, which is then utilized to obtain the extinction cross section in a retarded Mie scattering formalism. We show that such spherical resonators support unique plasmon dynamics: in the visible there is a new regime of coherently driven cluster-localized plasmons, while crossover to homogeneous response in the infrared predicts a delocalized shell plasmon.     

Coherent light scattering spectroscopy for supersonic flow measurements

A unified discussion on coherent light scattering spectroscopy and its spectral dependence on molecular gas velocity, temperature and density is presented. The feasibility of using coherent Raman spectroscopy techniques for nonintrusive measurements of supersonic flow parameters is demonstrated and recent laboratory as well as wind tunnel experiments are reviewed. In addition, the advantages of using coherent Rayleigh-Brillouin spectroscopy for measuring high pressure flows are discussed.     

Coherent inelastic electron scattering in LEED studies of As (0001)

The diffraction of low-energy electrons scattered inelastically from the As (0001) surface has been characterized. One prominent feature equivalent to loss followed by diffraction was observed photographically in the LEED display. The inverse process, diffraction plus loss, was present in energy distributions of LEED beams as measured with a high-angular resolution, variable position mini-analyzer and supported with spot photometry. The results indicate an inherent difficulty in obtaining LEED intensity data for As (0001) at E_p > 150 eV. In a further test of factors affecting LEED intensities, limitations to time-reversal invariance have also been observed and correlated with inelastic effects.     

Elastic and inelastic scattering of high-energy particles on the deuteron

The scattering amplitudes on the deuteron at small momentum transfers are described, taking into account the shadow corrections. In the framework of Regge pole theory, the inelastic shadow corrections are expressed in terms of the amplitudes of inelastic processes. The validity limit of the formulae thus obtained is discussed.     

The spatial coherence factor in light scattering from a system of independent particles

We derive the spatial coherence factor associated with the intensity correlation function of light scattered from N independent particles. The expression agrees with that derived by assuming a gaussian light field. We show also that the so-called cross-spectral purity condition is valid in this case. The applicability of this expression to the case of clipped intensity correlation function and to the case of strongly interacting particles are also discussed.