Hyper-Rayleigh light scattering from an aqueous suspension of purple membrane

Here we report the first observation of hyper-Rayleigh light scattering from bacteriorhodopsin in the form of an aqueous suspension of unoriented purple membranes. A typical purple membrane suspension used in our experiments contains approximately 10(8) randomly oriented purple membranes. Each purple membrane contains approximately 10(5) bacteriorhodopsin molecules in a two-dimensional crystallinearray. Hyper-Rayleigh light scattering is observed when the purple membrane suspension is illuminated with light that has a wavelength of 1064 nm. We propose that the 532-nm scattered light from each of the bacteriorhodopsin molecules in a single purple membrane is coherent, and that the scattered light from different purple membranes is incoherent. This proposal is supported by the following experimental observations: (a) the 532-nm light intensity is proportional to the square of the incident power, (b) the intensity of the 532-nm signal is linearly proportional to the concentration of purple membrane in solution, (c) the scattered 532-nm light is incoherent, (d) the scattered 532-nm light intensity decreases if the size of the purple membranes is reduced while the bacteriorhodopsin concentration is kept constant, and (e) the 532-nm light is due to the retinal chromophore of the bacteriorhodopsin molecule. The ratio of horizontal polarized hyper-Rayleigh scattered light to vertically polarized hyper-Rayleigh scattered light gives the angle (23 ± 4°) of the retinal axis with respect to the plane of the purple membrane. The hyperpolarizability of the bacteriorhodopsin molecule is found to be 5 ± 0.4 × 10(-27) esu.     

Determination of the characteristics of a suspension of particles from the spectrum of low-angle light scattering

A method is suggested for determining the concentration and properties of particles suspended in liquids based on combined analysis of low-angle light scattering spectra and absorption spectra in the 200–900 nm range. __________ Translated from Izmeritel'naya Tekhnika, No. 1, pp. 57–60, January, 2006.     

Analysis of light scattering from a cutting tool edge

The scattering of light from cutting tools is studied. The contribution of cutting tool edge parameters (height and width) to scattering patterns and the influence of side surface roughness on scattering patterns are investigated. An angle-limited integrated scattering method is developed and analyzed for fast determination of edge parameters.     

Resonance light scattering (RLS) detection of nanoparticle separations in a microelectrical field-flow fractionation system

In this study, resonance light scattering (RLS) is demonstrated as a detection methodology for real-time visualization of the electrical field-flow fractionation process. On-column RLS was used to monitor the fractionation of a bolus sample containing 40-, 60-, and 80-nm-diameter RLS Particles into individual particles and bands of particles. Optical detection using the RLS system was correlated to an on-chip electrical conductivity detector. Particle concentrations as low as 1.08/spl times/10/sup -12/ M (1 RLS Particle/1.54 pL) were detected using both the optical and electrical detection systems.     

Near-field microscopy by elastic light scattering from a tip

We describe ultraresolution microscopy far beyond the classical Abbe diffraction limit of one half wavelength (lambda/2), and also beyond the practical limit (ca. lambda/10) of aperture-based scanning near-field optical microscopy (SNOM). The 'apertureless' SNOM discussed here uses light scattering from a sharp tip (hence scattering-type or s-SNOM) and has no lambda-related resolution limit. Rather, its resolution is approximately equal to the radius a of the probing tip (for commercial tips, a < 20 nm) so that 10 nm is obtained in the visible (lambda/60). A resolution of lambda/500 has been obtained in the mid-infrared at lambda = 10 microm. The advantage of infrared, terahertz and even microwave illumination is that specific excitations can be exploited to yield specific contrast, e.g. the molecular vibration offering a spectroscopic fingerprint to identify chemical composition. S-SNOM can routinely acquire simultaneous amplitude and phase images to obtain information on refractive and absorptive properties. Plasmon- or phonon-resonant materials can be highlighted by their particularly high near-field signal level. Furthermore, s-SNOM can map the characteristic optical eigenfields of small, optically resonant particles. Lastly, we describe theoretical modelling that explains and predicts s-SNOM contrast on the basis of the local dielectric function.     

Determination of the structural properties of a columnar hexagonal liquid crystal by light scattering

In this study we examine a new computer model of light scattering. Light propagation through a columnar hexagonal liquid crystal has been represented by using a cylindrical model. Numerical aspects of the light scattering process, which are based on numerically solving Maxwell's equations, have been calculated for a liquid crystal. We describe in detail the circular cylindrical model for computing light scattering from a columnar hexagonal liquid crystal and present the results of benchmark computations. We report results of extensive calculation for oriented columnar molecular systems. Our results are compared with previous studies on light scattering by other materials.     

Simulation of light scattering from a particle upon a wafer surface

We simulated light scattering from a particle located on a smooth surface. We developed a new approach utilizing the discrete sources method based on a strict mathematical model for this scattering problem. The main features of the corresponding numerical algorithm are presented. The results of modeling and comparisons with other theoretical results and experimental data are shown as well.     

Green light stimulates terahertz emission from mesocrystal microspheres

The discovery of efficient sources of terahertz radiation has been exploited in imaging applications, and developing a nanoscale terahertz source could lead to additional applications. High-frequency mechanical vibrations of charged nanostructures can lead to radiative emission, and vibrations at frequencies of hundreds of kilohertz have been observed from a ZnO nanobelt under the influence of an alternating electric field. Here, we observe mechanical resonance and radiative emission at ～ 0.36 THz from core-shell ZnO mesocrystal microspheres excited by a continuous green-wavelength laser. We find that ～ 0.016% of the incident power is converted into terahertz radiation, which corresponds to a quantum efficiency of ～ 33%, making the ZnO microspheres competitive with existing terahertz-emitting materials. The mechanical resonance and radiation stem from the coherent photo-induced vibration of the hexagonal ZnO nanoplates that make up the microsphere shells. The ZnO microspheres are formed by means of a nonclassical, self-organized crystallization process, and represent a straightforward route to terahertz radiation at the nanoscale.     

Ellipsometry of light scattering from multilayer coatings

A scatterometer is extended and allows us to perform ellipsometric measurements on scattered light in each direction of space. Experimental data are given for single thin-film layers and optical coatings and reveal unexpected results. The phenomena are investigated by means of the electromagnetic theories of surface and bulk scattering that emphasize the role of partial correlation and localized defects.     

Neutron scattering from liquid 4He

In this lecture the study of excitations in quantum fluids and solids using neutrons is briefly introduced. The remainder focuses on liquid ⁴ He, giving a brief historical sketch of ideas on phonons and rotons, a survey of some recent neutron scattering data particularly on the temperature dependence of S(Q, ) and a new interpretation of phonons and rotons in superfluid ⁴He.Now at Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716.     

Magnetic field and concentration dependence of light scattering from a ferrofluid

Measurements of light scattering from a ferrofluid were undertaken as functions of both magnetic field and particle concentration. The results show that the distribution pattern of light intensity in space is a continuous banding perpendicular to the field direction. The light intensity weakens with increasing scattering angle. The experiments also indicate that the scattering coefficient increases both with the magnetic field and with the particle concentration and tends to saturate at higher field strengths. Finally, the experimental results are discussed in terms of an expanded theory of light scattering established by considering the widths of the chains formed in the ferrofluid as functions of both the magnetic field and the particle concentration.     

Measurements of light scattering from glass substrates by total integrated scattering

A total integrated scattering (TIS) measurement was performed to investigate the surface and volume scattering of K9 glass substrates with low reflectance. Ag layers with thicknesses of 60 nm were deposited on the front and back surfaces of the K9 glass substrates by the magnetron sputtering technique. Surface scattering of the K9 glass substrate was obtained by the TIS measurement of the Ag layers on the assumption that the Ag layers and the K9 substrate had the same surface profile. Volume scattering of the substrates was deduced by subtracting the front and back surface scattering from the total scattering of the substrates.     

Angular distribution of the forward light scattering from a quartz fiber

Using a new technique based on the fanning of a coherent light beam in a photorefractive BaTiO(3) crystal, we have measured the angular distribution of forward light scattering by quartz fibers of radii from 15 to 30 μm. Data have been obtained over the angular range 0° to 0.3° and are in good agreement with theory.     

Modeling light scattering from Diesel soot particles

The Mie model is widely used to analyze light scattering from particulate aerosols. The Diesel particle scatterometer, for example, determines the size and optical properties of Diesel exhaust particles that are characterized by the measurement of three angle-dependent elements of the Mueller scattering matrix. These elements are then fitted by Mie calculations with a Levenburg-Marquardt optimization program. This approach has achieved good fits for most experimental data. However, in many cases, the predicted complex index of refraction was smaller than that for solid carbon. To understand this result and explain the experimental data, we present an assessment of the Mie model by use of a light-scattering model based on the coupled-dipole approximation. The results indicate that the Mie calculation can be used to determine the largest dimension of irregularly shaped particles at sizes characteristic of Diesel soot and, for particles of known refractive index, tables can be constructed to determine the average porosity of the particles from the predicted index of refraction.     

Large-angle in-plane light scattering from rough surfaces

An in-plane light scattering setup that is capable of measuring large azimuthal scattering angles is presented. This type of measurement makes it easier to probe large k(parallel) at a fixed k(perpendicular) value (k(parallel) and k(perpendicular) are momentum transfer vectors parallel and perpendicular to the surface, respectively). Therefore the system allows us to explore small lateral scale and large vertical roughness (approximately lambda, the wavelength of the probe beam) of a rough surface. In-plane intensity measurements from a rough backside Si wafer and a Cu thin-film surface are reported. The structure factor that is related to surface roughness parameters is obtained from the measured in-plane intensity profiles. Both scalar (Beckmann-Kirchhoff) and vector (Rayleigh-Rice) theories have been applied to interpret the experimental data. The roughness parameters obtained from the scattering measurements are compared with those measured by atomic-force microscopy.     

Circularly symmetric light scattering from nanoplasmonic spirals

In this paper, we combine experimental dark-field imaging, scattering, and fluorescence spectroscopy with rigorous electrodynamics calculations in order to investigate light scattering from planar arrays of Au nanoparticles arranged in aperiodic spirals with diffuse, circularly symmetric Fourier space. In particular, by studying the three main types of Vogel's spirals fabricated by electron-beam lithography on quartz substrates, we demonstrate polarization-insensitive planar light diffraction in the visible spectral range. Moreover, by combining dark-field imaging with analytical multiparticle calculations in the framework of the generalized Mie theory, we show that plasmonic spirals support distinctive structural resonances with circular symmetry carrying orbital angular momentum. The engineering of light scattering phenomena in deterministic structures with circular Fourier space provides a novel strategy for the realization of optical devices that fully leverage on enhanced, polarization-insensitive light-matter coupling over planar surfaces, such as thin-film plasmonic solar cells, plasmonic polarization devices, and optical biosensors.     

Elastic light scattering from single microparticles on a femtosecond time scale

Experimentally measured and theoretically calculated elastic light-scattering spectra from single microparticles illuminated by 100-fs pulses are presented. Although in the theoretical calculation only a single incoming femtosecond laser pulse was used, the spectral behavior of scattered light shows all the features seen in the experimental spectrum from many femtosecond pulses, including morphology-dependent resonances (MDR's). The good agreement between experimental and theoretical elastic light-scattering data has stimulated a theoretical investigation of the time-dependent behavior of the elastically scattered light from a single microparticle on a femtosecond time scale. Since the spatial pulse length of the incoming laser pulse is smaller than the particle circumference, the temporal behavior of reflection, diffraction, refraction, and coupling into MDR's can be distinguished. Since the time-dependent scattering is strongly dependent on particle size, refractive index, and pulse chirp, it may be possible to encode several bits of information into a single laser pulse and therefore to increase optical data communication rates.     

Size-shape determination of nonspherical particles in suspension by means of full and depolarized static light scattering

Full and depolarized static light-scattering (LS) experiments have been carried out to characterize the size and shape of colloidal suspensions. Results have been compared with theoretical predictions following the extended-boundary-condition method (T-matrix) formalism for scattering by nonspherical particles. Theory-to-experiment data fitting has yielded size-shape data that compare well with electron-microscopy determinations. Depolarized light-scattering has been found to be an especially useful tool to use to find the correct geometrical parameters of the suspended particles. Size (though not shape) is also correctly fitted through full LS experiments.