Showing papers on "Light scattering published in 2002"

Scattering, Absorption, and Emission of Light by Small Particles

Abstract: Preface Acknowledgements Part I. Basic Theory of Electromagnetic Scattering, Absorption, and Emission: 1. Polarization characteristics of electromagnetic radiation 2. Scattering, absorption, and emission of electromagnetic radiation by an arbitrary finite particle 3. Scattering, absorption and emission by collections of independent particles 4. Scattering matrix and macroscopically isotropic and mirror-symmetric scattering media Part II. Calculation and Measurement of Scattering and Absorption Characteristics of Small Particles: 5. T-matrix method and Lorenz-Mie theory 6. Miscellaneous exact techniques 7. Approximations 8. Measurement techniques Part III. Scattering and Absorption Properties of Small Particles and Illustrative Applications: 9. Scattering and absorption properties of spherical particles 10. Scattering and absorption properties of nonspherical particles Appendices References Index.

On the Absorption Cross Section of CdSe Nanocrystal Quantum Dots

Abstract: The linear absorption cross section is a crucial parameter to the design of nanocrystal quantum dot devices and to the interpretation of spectroscopic data. We measure and report the size-dependent absorption cross section of CdSe nanocrystal quantum dots. We compare the results for absorption far above the band edge, where the quantum dot density of states may be approximated as a continuum, to simple theoretical models of light scattering from light-absorbing small particles. Excellent agreement with theory is found for dilute dispersions in hexane. We find that for absorption at 350 nm the per particle absorption cross section Cabs (in cm2) for CdSe is Cabs = (5.501 × 105)a3 cm-1, where a is the particle radius in cm. The absorption cross section is observed to be largely insensitive to the solvent refractive index. Detailed modeling of the effect of the ligand shell may be necessary to understand the lack of sensitivity of the absorption properties of nanocrystal quantum dots to the refractive index o...

Neutrons, X-rays and light : scattering methods applied to soft condensed matter

Abstract: Part I. Using general principles 1. Introduction to scattering experiments (P.N. Pusey) 2. Scattering experiments: Experimental aspects, initial data reduction and absolute calibration (P. Lindner) 3. General theorems in small-angle scattering (O. Spalla) 4. The inverse scattering problem in small angle scattering (O. Glatter) 5. Fourier transformation and deconvolution (O. Glatter) Part II. Methods 6. Instrumentation for small-angle x-ray and neutron scattering and instrumental smearing effects (J.S. Pedersen) 7. Contrast and contrast variaion in neutron, x-ray and light scatering (P. Schurtenberger) 8. Static light scattering of large systems (O. Glatter) 9. Dynamic light scattering (P.N. Pusey) 10.Inelastic neutron scattering: Dynamics of polymers (R. Zorn) Part III. Revealing microstructures of soft condensed matter 11. Static properties of polymers (P. Schurtenberger) 12. Surfactant micelles and bilayers: Shapes and interactions (G. Porte) 13. Scattering by microemulsions (Th. Zemb) 14. Interacting colloidal suspensions (R. Klein) 15. Monte Carlo simulation techniques applied in the analysis of small-angle scattering data from colloids and polymer system (J.S. Pedersen) 16. Modelling of small-angle scattering data from colloids and polymer systems (J.S. Pedersen) Part IV. Special Applications 17. Scattering experiments under external constraints: SANS and Shear flow (P. Lindner) 18. Using synchrotron radiation to study structure development in polymer processing (A.J.Ryan) 19. Biological applications of small-angle neutron scattering (R.P. May) 20. Light scattering in turbid suspensions, a tutorial (J. Ricka) 21. Use of scattering methods in chemical industr - SAXS an SANS from fibers and films (J. Rieger) Subject Index

Review of polarization sensitive optical coherence tomography and Stokes vector determination.

Abstract: Polarization sensitive optical coherence tomography (PS-OCT) provides depth resolved measurements of the polarization state of light reflected from turbid media such as tissue. The theory and calculation of the Stokes vector of light reflected from turbid media is described and application of PS-OCT to contemporary biomedical imaging problems is given. Measurement of the depth resolved Stokes parameters allows determination of the degree of polarization and optical axis orientation in turbid media that can be modeled as a linear retarder. Effect of multiple scattering and speckle on the accuracy and noise of the computed Stokes parameters is discussed. Future directions for development of PS-OCT instrumentation for biological and medical applications is given.

Handbook of Optical Biomedical Diagnostics

Abstract: Part 1 Physics of Light-Tissue Interaction - Diagnostical Aspects: Introduction to Light Scattering by Biological Objects Optics of Blood Propagation of Pulses and Photon Density Waves in Turbid Media Coherence Phenomena and Statistical Properties of Multiply Scattered Light Tissue Phantoms. Part 2 Pulse and Frequency-Domain Techniques for Tissue Spectroscopy and Imaging: Time-Resolved Imaging in Diffusive Media Frequency-Domain Techniques for Tissue Spectroscopy and Imaging Monitoring of Brain Activity With Near-Infrared Spectroscopy Signal Quantification and Localization in Tissue Near-Infrared Spectroscopy Time-Resolved Detection of Optoacoustic Profiles for Measurement of Optical Energy Distribution in Tissues. Part 3 Scattering, Fluorescence, and Infrared Fourier Transform Spectroscopy of Tissues: Light Back Scattering Spectroscopy of Epithelial Tissues - Principles and Applications Reflectance and Fluorescence Spectroscopy of Human Skin in Vivo Infrared and Raman Spectroscopy of Human Skin in Vivo Fluorescence Technologies in Biomedical Diagnostics. Part 4 Coherent-Domain Methods for Biological Flows and Tissue Ultrastructure Monitoring: Speckle and Doppler Methods of Blood and Lymph Flow Monitoring Real-Time Imaging of Microstructure and Blood Flows Using Optical Coherence Tomography Speckle Technologies for Monitoring and Imaging of Tissues and Tissue-Like Phantoms Optical Assessment of Tissue Mechanics.

Drastic reduction of plasmon damping in gold nanorods

Abstract: Summary form only given. Samples of gold nanospheres and nanorods are investigated in a conventional dark-field microscope For spectral investigations, the scattered light from single particles is focused with the microscope onto the entrance slit of a spectrometer coupled to a cooled CCD camera. This dark-field spectroscopy provides a nearly background free measuring technique and allows to record spectra with excellent signal to noise ratio.

Surface characterization techniques for determining the root-mean-square roughness and power spectral densities of optical components

Abstract: Surface topography and light scattering were measured on 15 samples ranging from those having smooth surfaces to others with ground surfaces. The measurement techniques included an atomic force microscope, mechanical and optical profilers, confocal laser scanning microscope, angle-resolved scattering, and total scattering. The samples included polished and ground fused silica, silicon carbide, sapphire, electroplated gold, and diamond-turned brass. The measurement instruments and techniques had different surface spatial wavelength band limits, so the measured roughnesses were not directly comparable. Two-dimensional power spectral density (PSD) functions were calculated from the digitized measurement data, and we obtained rms roughnesses by integrating areas under the PSD curves between fixed upper and lower band limits. In this way, roughnesses measured with different instruments and techniques could be directly compared. Although smaller differences between measurement techniques remained in the calculated roughnesses, these could be explained mostly by surface topographical features such as isolated particles that affected the instruments in different ways.

Non-spherical aerosol retrieval method employing light scattering by spheroids and it application to AERONET data

Abstract: Received 4 December 2001; revised 5 February 2002; accepted 8 February 2002; published 24 May 2002. [1] Numerous studies indicate the need to account for particle non-sphericity in modeling the optical properties of dustlike aerosols. The methods for simulating the scattering of light by various non-spherical shapes have rapidly evolved over the last two decades. However, the majority of aerosol remote-sensing retrievals still rely on the Mie theory because retrievals accounting for particle non-sphericity are not as well defined methodologically and are demanding computationally. We propose a method for the retrieval of the optical properties of non-spherical aerosol based on the model of a shape mixture of randomly oriented polydisperse spheroids. This method is applied to angular and spectral radiation measurements from the Aerosol Robotic Network (AERONET) in locations influenced by desert dust. Comparisons with Mie-based retrievals show a significant improvement in dust-particle phase functions, size distributions, and refractive indices. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0933 Exploration Geophysics: Remote sensing; 0994 Exploration Geophysics: Instruments and techniques

Collective cooling and self-organization of atoms in a cavity.

Abstract: We theoretically investigate the correlated dynamics of N coherently driven atoms coupled to a standing-wave cavity mode. For red detuning between the driving field and the cavity as well as the atomic resonance frequencies, we predict a light force induced self-organization of the atoms into one of two possible regular patterns, which maximize the cooperative scattering of light into the cavity field. Kinetic energy is extracted from the atoms by superradiant light scattering to reach a final kinetic energy related to the cavity linewidth. The self-organization starts only above a threshold of the pump strength and atom number. We find a quadratic dependence of the cavity mode intensity on the atom number, which demonstrates the cooperative effect.

Propagation of polarized light in birefringent turbid media: a Monte Carlo study.

Abstract: A detailed study, based on a Monte Carlo algorithm, of polarized light propagation in birefringent turbid media is presented in this paper. Linear birefringence, which results from the fibrous structures, changes the single scattering matrix and alters the polarization states of photons propagating in biological tissues. Some Mueller matrix elements of light backscattered from birefringent anisotropic turbid media present unusual intensity patterns compared with those for nonbirefringent isotropic turbid media. This result is in good agreement with the analytic results based on the double-scattering model. Degree of polarization, Stokes parameters, and diffuse reflectance as functions of linearly birefringent parameters based on numerical results and theoretical analysis are discussed and compared in an effort to understand the essential physical processes of polarized light propagation in fibrous tissues.

Resonant light scattering from individual Ag nanoparticles and particle pairs

Abstract: Light scattering by individual Ag nanoparticles and structures have been studied spectroscopically. Individual particles were selected and manipulated with a micromanipulator installed inside a scanning electron microscope (SEM). With typical particle dimensions of some 100 nm, the plasma resonances of particles and the coupled modes of particle pairs were observed in the visible region. The polarization dependence of the resonance frequencies strongly reflects the shape anisotropy; the effect that would be averaged out for experiments on ensembles. With a simple approximation to take the glass substrate into account, the results are in good agreement with the analytical calculations by Mie scattering, and with numerical calculations by the finite-difference time-domain method, both of which are performed with the morphological parameters obtained from the SEM observation for the corresponding particle or particle pair.

Organic light-emitting devices for illumination quality white light

Abstract: A method of generating white light by combining a blue organic light-emitting diode with a down-conversion phosphor system is presented. It is demonstrated that the use of the down-conversion phosphor system actually leads to an overall power efficiency increase, an effect attributed to the high quantum efficiency of phosphor materials and the presence of light scattering in the phosphor layers. It is also shown that this approach permits the generation of illumination quality white light over the full range of color temperatures required for lighting applications. For the model device demonstrated in this work, an overall electrical to optical power conversion efficiency of 1.3% was achieved at a brightness of 1080 cd/m 2 .

Spontaneous and stimulated Brillouin scattering gain spectra in optical fibers

Abstract: We study the Brillouin scattering behavior in several single-mode fibers with different waveguide characteristics in terms of their longitudinal mode structures in the gain spectrum, linewidth narrowing, and stimulated Brillouin scattering (SBS) threshold levels. Evolution from spontaneous to SBS is investigated by monitoring the Brillouin line-shape and the behavior of the longitudinal acoustooptic resonance modes that exist in the core. We compare our results with the current theory of Brillouin scattering generated from noise in the undepleted pump approximation. We also present experimentally Brillouin gain spectra in the highly depleted pump regime, where there is no analytical solution, by showing the evolution of the gain spectrum as a function of the injected laser intensity.

Microrheology of polyethylene oxide using diffusing wave spectroscopy and single scattering

Abstract: Experiments investigating the local viscoelastic properties of a simple uncross-linked flexible polymer are performed on polyethylene oxide solutions in the semidilute regime using polystyrene beads of varying sizes and surface chemistry as probes. We measure the thermal motions of the beads to obtain the elastic and viscous moduli of our sample. Two different dynamic light scattering techniques, diffusing wave spectroscopy and quasielastic light scattering (QELS), are used to determine the dynamics of the probe particles. Diffusing wave spectroscopy probes the short time dynamics of the scatterers while QELS or single scattering measures the dynamics at larger times. This results in a larger frequency overlap of the data obtained from the microrheological techniques with the data obtained from the conventional bulk measurements. The moduli are estimated using a modified algebraic form of the generalized Stokes-Einstein equation. Comparison of microrheology with bulk measurements shows excellent similarity confirming the applicability of this method for simple, uncross-linked polymeric systems.

An experiment to measure Mie and Rayleigh total scattering cross sections

Abstract: We present an undergraduate-level experiment using a conventional absorption spectrophotometer to measure the wavelength dependence of light scattering from small dielectric spheres suspended in water. The experiment yielded total scattering cross-section values throughout the visible region that were in good agreement with theoretical values predicted by the Rayleigh and Mie theories.

The Principles of Nonlinear Optics

Abstract: Introduction. Nonlinear Optical Susceptibilities. General Description of Wave Propagation in Nonlinear Media. Electrooptical and Magnetooptical Effects. Optical Rectification and Optical Field-Induced Magnetization. Sum-Frequency Generation. Harmonic Generation. Difference Frequency Generation. Parametric Amplification and Oscillation. Stimulated Raman Scattering. Stimulated Light Scattering. Two-Photon Absorption. High-Resolution Nonlinear Optical Spectroscopy. Four-Wave Mixing. Four-Wave Mixing Spectroscopy. Optical-Field-Induced Birefringence. Self-Focusing. Multiphoton Spectroscopy. Detection of Rare Atoms and Molecules. Laser Manipulation of Particles. Transient Coherent Optical Effects. Strong Interaction of Light with Atoms. Infrared Multiphoton Excitation and Dissociation of Molecules. Laser Isotope Separation. Surface Nonlinear Optics. Nonlinear Optics in Optical Waveguides. Optical Breakdown. Nonlinear Optical Effects in Plasmas. Index.

Electrically controlled light scattering with single metal nanoparticles

Abstract: A concept to electrically control the scattering of light is introduced. The idea is to embed noble metal nanoparticles in an electro-optical material such as a liquid crystal in order to induce a spectral shift of the particle plasmon resonance by applying an electric field. Light scattering experiments on single gold nanoparticles show that spherically shaped nanoparticles become optically spheroidal when covered by an anisotropic liquid crystal. The two particle plasmon resonances of the optically spheroidal gold nanoparticles can be spectrally shifted by up to 50 meV when electric fields of more than 10 kV/cm are applied.

High-Sensitivity Detection of DNA Hybridization on Microarrays Using Resonance Light Scattering

Abstract: The application of resonance light scattering (RLS) particles for high-sensitivity detection of DNA hybridization on cDNA microarrays is demonstrated. Arrays composed of ∼2000 human genes (“targets”) were hybridized with colabeled (Cy3 and biotin) human lung cDNA probes at concentrations ranging from 8.3 ng/μL to 16.7 pg/μL. After hybridization, the arrays were imaged using a fluorescence scanner. The arrays were then treated with 80-nm-diameter gold RLS Particles coated with anti-biotin antibodies and imaged in a white light, CCD-based imaging system. At low probe concentrations, significantly more genes were detected by RLS compared to labeling by Cy3. For example, for hybridizations with a probe concentration of 83.3 pg/μL, ∼1150 positive genes were detected using RLS compared to ∼110 positive genes detected with Cy3. In a differential gene expression experiment using human lung and leukemia RNA samples, similar differential expression profiles were obtained for labeling by RLS and fluorescence technol...

Polarized angular dependent spectroscopy of epithelial cells and epithelial cell nuclei to determine the size scale of scattering structures.

Abstract: An understanding of the relationship between tissue structures and light scattering from tissue will help facilitate the development and acceptance of noninvasive optical diagnostics including elastic scattering spectroscopy, diffuse reflectance, and optical coherence tomography. For example, a quantitative model of the structures that scatter light in epithelial cells would allow determination of what structures control the characteristics of in vivo light transport measurements and subsequently could provide a detailed relationship between cellular structures and optical measurements. We have determined the size distribution of refractive index structure variations in epithelial cells as well as in nuclei isolated from epithelial cells from measurements of the angular dependence of polarized light scattering. The quantitative size distributions we obtained for both whole cells and isolated nuclei include particles with effective radii of 2 µm to 10 nm or less and contain orders of magnitude more small particles than large particles. These results demonstrate that not only are biological cells very heterogeneous, but so are the nuclei within them. Light scattering is likely sensitive to structures smaller than those commonly investigated by standard pathology methods.

Comparative study of polarized light propagation in biologic tissues.

Abstract: We report the depolarization of light scattered by a variety of birefringent and nonbirefringent tissues. We used Stokes polarime- try to investigate how scatterer structures in each tissue contribute to the depolarization of linearly versus circularly polarized light propa- gating through that tissue. Experiments were performed on porcine blood, fat, tendon, artery, and myocardium. The results indicate that the two incident polarization states are depolarized differently de- pending on the structure of the sample. As seen in sphere suspensions, for tissues containing dilute Mie scatterers, circularly polarized light is maintained preferentially over linearly polarized light. For more dense tissues, however, the reverse is true. The results illustrate situations where polarized light will provide an improvement over unpolarized light imaging, information that is crucial to optimizing existing pola- rimetric imaging techniques. © 2002 Society of Photo-Optical Instrumentation En-

Composite Plasmon Resonant Nanowires

Abstract: We present an experimental study of the polarization-dependent scattering of light from homogeneous and multisegment silver, gold, and nickel nanowires. The metallic nanowires are prepared within a polycarbonate membrane template by a combination of electroplating (gold and nickel) and electroless (silver) growth processes. The size range of the nanowire segments is such that surface plasmon resonances are supported, dominating the optical spectra. We characterize the light scattering properties of individual composite nanowires using an optical microscope configured for single particle spectroscopy. Because of the scattering efficiency associated with the plasmon resonance, very narrow (∼30 nm diameter) nanowires can be readily observed under white-light illumination, with the spectral characteristics of each subsection easily distinguishable. Because of their compactness, these simply prepared multiisegment plasmon resonant nanowires are capable of hosting a large number of segment sequences over a comp...

Organic light-emitting device having enhanced light extraction efficiency

Abstract: An enhanced light extraction OLED device including a transparent substrate; light scattering layer disposed over a first surface of the transparent substrate; a transparent first electrode layer disposed over the light scattering layer; an organic EL element disposed over the transparent first electrode layer and including one or more organic layers but at least one light emitting layer in which light is produced; and a transparent second electrode layer disposed over the organic EL element.

Rearrangements in hard-sphere glasses under oscillatory shear strain.

Abstract: We investigate particle rearrangements in colloidal glasses subjected to oscillatory shear strain by the technique of light scattering (LS) echo. LS echo directly follows the motion of the particles through peaks (echoes) in the intensity autocorrelation function; the height of the peak measures the reversible motion in the sample. Polydisperse hard-sphere poly-methylmethacrylate particles were used to avoid crystallization under shear. The yielding behavior is monitored through irreversible particle rearrangements at several volume fractions in the glass phase region. At high volume fractions the glasses are found to yield at strains as high as 15% while the irreversible rearrangements have a more gradual onset with strain for low volume fraction glasses. The behavior of high order echoes at long times is related to the effects of shear on the frozen-in fluctuations of the glass.

Light scattering by dust and anthropogenic aerosol at a remote site in the Negev desert, Israel

Abstract: [1] We investigated aerosol optical properties, mass concentration, and chemical composition over a 2 year period at a remote site in the Negev desert, Israel (Sde Boker, 30° 51′N, 34° 47′E, 470 m above sea level). Light-scattering measurements were made at three wavelengths (450, 550, and 700 nm), using an integrating nephelometer, and included the separate determination of the backscatter fraction. Aerosol coarse and fine fractions were collected with stacked filter units; mass concentrations were determined by weighing, and the chemical composition by proton-induced X-ray emission and instrumental neutron activation analysis. The total scattering coefficient at 550 nm showed a median of 66.7 Mm−1(mean value 75.2 Mm−1, standard deviation 41.7 Mm−1) typical of moderately polluted continental air masses. Values of 1000 Mm−1and higher were encountered during severe dust storm events. During the study period, 31 such dust events were detected. In addition to high scattering levels, they were characterized by a sharp drop in the Angstrom coefficient (i.e., the spectral dispersion of the light scattering) to values near zero. Mass-scattering efficiencies were obtained by a multivariate regression of the scattering coefficients on dust, sulfate, and residual components. An analysis of the contributions of these components to the total scattering observed showed that anthropogenic aerosol accounted for about 70% of scattering. The rest was dominated by the effect of the large dust events mentioned above and of small dust episodes typically occurring during midafternoon.

Vector radiative transfer equation for arbitrarily shaped and arbitrarily oriented particles: a microphysical derivation from statistical electromagnetics

Abstract: The concepts of statistical electromagnetics are used to derive the general radiative transfer equation (RTE) that describes multiple scattering of polarized light by sparse discrete random media consisting of arbitrarily shaped and arbitrarily oriented particles. The derivation starts with the volume integral and Lippmann-Schwinger equations for the electric field scattered by a fixed N-particle system and proceeds to the vector form of the Foldy-Lax equations and their approximate far-field version. I then assume that particle positions are completely random and derive the vector RTE by applying the Twersky approximation to the coherent electric field and the Twersky and ladder approximations to the coherency dyad of the diffuse field in the limit N → ∞. The concluding section discusses the physical meaning of the quantities that enter the general vector RTE and the assumptions made in its derivation.

Mechanisms of Ultrasonic Modulation of Multiply Scattered Coherent Light

Abstract: An analytic model of the ultrasonic modulation of multiply scattered coherent light in scattering media is provided. The model is based on two mechanisms: the ultrasonic modulation of the index of refraction, which causes a modulation of the optical path lengths between consecutive scattering events, and the ultrasonic modulation of the displacements of Rayleigh scatterers, which causes a modulation of optical path lengths upon each scattering event. Multiply scattered light accumulates modulated optical path lengths along its path. Consequently, the intensity of the speckles that are formed by the multiply scattered light is modulated. In water solutions, for example, the contribution from the index of refraction is slightly less than the contribution from displacement when the scattering mean free path is less than a critical fraction of the acoustic wavelength, and it becomes increasingly greater than the contribution from displacement beyond this critical point.

Diffuse-reflectance spectroscopy from 500 to 1060 nm by correction for inhomogeneously distributed absorbers.

Abstract: Diffuse-reflectance spectroscopy for measurement of the absorption and scattering coefficients of biological tissue produces reliable results for wavelengths from 650 to 1050 nm. Implicitly, this approach assumes homogeneously distributed absorbers. A correction factor is introduced for inhomogeneous distribution of blood concentrated in discrete cylindrical vessels. This factor extends the applicability of diffusion theory to lower wavelengths. We present measurements of in vivo optical properties in the wavelength range 500-1060 nm.

Collapse of a Monolayer by Three Mechanisms

Abstract: The collapse of monolayers of 2-hydroxytetracosanoic acid at the air/water interface has been examined by measurements of surface pressure−area isotherms and imaging with light scattering microscop...