Showing papers on "Light scattering published in 2015"
TL;DR: A single-junction polymer solar cell with an efficiency of 10.1% is demonstrated by using deterministic aperiodic nanostructures for broadband light harvesting with optimum charge extraction through self-enhanced absorption due to collective effects, including pattern-induced anti-reflection and light scattering.
Abstract: A single-junction polymer solar cell with an efficiency of 10.1% is demonstrated by using deterministic aperiodic nanostructures for broadband light harvesting with optimum charge extraction. The performance enhancement is ascribed to the self-enhanced absorption due to collective effects, including pattern-induced anti-reflection and light scattering, as well as surface plasmonic resonance, together with a minimized recombination probability.
1,002 citations
TL;DR: This review summarizes recently developed feedback-based approaches for focusing light inside and through scattering objects.
Abstract: Light scattering was thought to be the fundamental limitation for the depth at which optical imaging methods can retain their resolution and sensitivity. However, it was shown that light can be focused inside even the most strongly scattering objects by spatially shaping the wavefront of the incident light. This review summarizes recently developed feedback-based approaches for focusing light inside and through scattering objects
363 citations
TL;DR: In this article, the authors describe the physics that explains the optical properties of disordered nanostructures and scattering used to develop the random lasers, particularly discussing the role of modes in random lasers.
235 citations
TL;DR: In this paper, the suppression and control of multiple light scattering events are investigated because they offer the possibility of optical focusing and imaging through biological tissues, and they may open new avenues for diagnosis and treatment of several human diseases.
219 citations
TL;DR: A review of light scattering applications in the field of particle characterization can be found in this paper, where the authors address static light scattering (the measurement of scattering intensities due to light-particle interaction at various spatial locations), dynamic light scattering, and scattering tracking analysis (the tracking of particle movement through scattering measurement).
210 citations
Book•
29 Jun 2015
TL;DR: In this article, the authors present a method for the determination of molecular structure of polymers and their distribution in dilute solutions using a light scattering detector and a column-packing approach.
Abstract: Preface. 1 Polymers. 1.1 Introduction. 1.2 Molecular Structure of Polymers. 1.2.1 Macromolecules in Dilute Solution. 1.3 Molar Mass Distribution. 1.3.1 Description of Molar Mass Distribution. 1.3.1.1 Distribution Functions. 1.3.1.2 Molar Mass Averages. 1.4 Methods for the Determination of Molar Mass. 1.4.1 Method of End Groups. 1.4.2 Osmometry. 1.4.2.1 Vapor Pressure Osmometry. 1.4.2.2 Membrane osmometry. 1.4.3 Dilute Solution Viscometry. 1.4.3.1 Properties of Mark-Houwink Exponent. 1.4.3.2 Molecular Size from Intrinsic Viscosity. 1.4.3.3 Dependence of Intrinsic Viscosity on Polymer Structure, Temperature and Solvent. 1.4.4 Matrix Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry. 1.4.5 Analytical Ultracentrifugation. 1.5 Keynotes. 1.6 References. 2 Light Scattering. 2.1 Theory and Basic Principles. 2.2 Types of Light Scattering. 2.2.1 Static Light Scattering. 2.2.1.1 Particle Scattering Functions. 2.2.1.2 Light Scattering Formalisms. 2.2.1.3 Processing the Experimental Data. 2.2.2 Dynamic Light Scattering. 2.3 Light Scattering Instrumentation. 2.4 Specific Refractive Index Increment. 2.5 Light Scattering in Batch and Chromatography Mode. 2.6 Parameters Affecting Accuracy of Molar Mass Determined by Light Scattering. 2.7 Examples of Light Scattering Measurement in Batch Mode. 2.8 Keynotes. 2.9 References. 3 Size Exclusion Chromatography. 3.1 Introduction. 3.2 Separation Mechanisms. 3.2.1 Steric Exclusion. 3.2.2 Restricted Diffusion. 3.2.3 Separation by Flow. 3.2.4 Peak Broadening and Separation Efficiency. 3.2.5 Secondary Separation Mechanisms. 3.3 Instrumentation. 3.3.1 Solvents. 3.3.2 Columns and Column Packing. 3.3.3 Detectors. 3.3.3.1 UV Detector. 3.3.3.2 Refractive Index Detector. 3.3.3.3 Infrared Detector. 3.3.3.4 Evaporative Light Scattering Detector. 3.3.3.5 Viscosity Detector. 3.3.3.6 Light Scattering Detector. 3.3.3.7 Other Types of Detectors. 3.4 Column Calibration. 3.4.1 Universal Calibration. 3.4.2 Flow Marker. 3.5 SEC Measurements and Data Processing. 3.5.1 Sample Preparation. 3.5.1.1 Sample Derivatization. 3.5.2 Determination of Molar Mass and Molar Mass Distribution. 3.5.3 Reporting Results. 3.5.4 Characterization of Chemical Composition of Copolymers and Polymer Blends. 3.5.5 Characterization of Oligomers. 3.5.6 Influence of Separation Conditions. 3.5.7 Accuracy, Repeatability and Reproducibility of SEC Measurements. 3.6 Applications of SEC. 3.7 Keynotes. 3.8 References. 4 Combination of SEC and Light Scattering. 4.1 Introduction. 4.2 Data Collection and Processing. 4.2.1 Processing MALS Data. 4.2.1.1 Debye Fit Method. 4.2.1.2 Zimm Fit Method. 4.2.1.3 Berry fit Method. 4.2.1.4 Random Coil Fit Method. 4.2.1.5 Influence of Light Scattering Formalism on Molar Mass and RMS Radius. 4.2.2 Determination of Molar Mass and RMS Radius Averages and Distributions. 4.2.3 Chromatogram Processing. 4.2.4 Influence of Concentration and Second Virial Coefficient. 4.2.5 Repeatability and Reproducibility. 4.2.6 Accuracy of Results. 4.3 Applications of SEC-MALS. 4.3.1 Determination of Molar Mass Distribution. 4.3.2 Fast Determination of Molar Mass. 4.3.3 Characterization of Complex Polymers. 4.3.3.1 Branched Polymers. 4.3.3.2 Copolymers and Polymer Blends. 4.3.4 Conformation Plots. 4.3.5 Mark-Houwink Plots. 4.4 Keynotes. 4.5 References. 5 Asymmetric Flow Field Flow Fractionation. 5.1 Introduction. 5.2 Theory and Basic Principles. 5.2.1 Separation Mechanisms. 5.2.2 Resolution and Band Broadening. 5.3 Instrumentation. 5.4 Measurements and Data Processing. 5.4.1 Influence of Separation Conditions. 5.4.1.1 Isocratic and Gradient Experiments. 5.4.1.2 Overloading. 5.4.2 Practical Measurements. 5.5 A4F Applications. 5.6 Keynotes. 5.7 References. 6 Characterization of Branched Polymers. 6.1 Introduction. 6.2 Detection and Characterization of Branching. 6.2.1 SEC Elution Behavior of Branched Polymers. 6.2.2 Distribution of Branching. 6.2.3 Average Branching Ratios. 6.2.4 Other Methods for the Identification and Characterization of Branching. 6.3 Examples of Characterization of Branching. 6.4 Keynotes. 6.5 References. Symbols. Abbreviations. Index.
203 citations
Book•
08 Aug 2015
TL;DR: A survey of ET of rarefied Monatomic Gases can be found in this paper, where a theory of Polyatomic Rarefied Gas and Dense Gas is presented.
Abstract: 1 Introduction.- 2 Mathematical Structure.- 3 Waves in Hyperbolic Systems.- 4 Survey of ET of Rarefied Monatomic Gases.- 5 ET Theory of Polyatomic Rarefied Gas and Dense Gas.- 6 Maximum entropy principle for rarefied polyatomic gases.- 7 Stationary heat conduction in a polyatomic gas at rest.- 8 Linear Wave in Polyatomic Gas.- 9 Shock Wave.- 10 Fluctuating hydrodynamics.- 11 Light scattering in Polyatomic Gas.- 12 ET6 Theory of Polyatomic Rarefied Gas and Dense Gas.- 13 Non linear ET6.- 14 Molecular ET Theory of Polyatomic Rarefied Gas.- 15 ET of dense gas with 6 moments.- 16 Mixture of Gases.- 17 Hyperbolic Parabolic Limit, Max wellian iteration and Objectivity.
199 citations
TL;DR: The anti-Stokes background is highly temperature dependent and is shown to be related to the thermal occupation of electronic states within the metal via a simple model, which suggests new routes to enhance SERS sensitivities, as well as providing ubiquitous and calibrated real-time temperature measurements of nanostructures.
Abstract: Temperature-dependent surface-enhanced Raman scattering (SERS) is used to investigate the photoluminescence and background continuum always present in SERS but whose origin remains controversial. Both the Stokes and anti-Stokes background is found to be dominated by inelastic light scattering (ILS) from the electrons in the noble metal nanostructures supporting the plasmon modes. The anti-Stokes background is highly temperature dependent and is shown to be related to the thermal occupation of electronic states within the metal via a simple model. This suggests new routes to enhance SERS sensitivities, as well as providing ubiquitous and calibrated real-time temperature measurements of nanostructures.
195 citations
TL;DR: In this paper, the first Kerker's condition for a spherical particle shape was realized, at which the backward scattering practically vanishes for some combination of refractive index and particle size.
Abstract: High-refractive index dielectric nanoparticles may exhibit strong directional forward light scattering at visible and near-infrared wavelengths due to interference of simultaneously excited electric and magnetic dipole resonances. For a spherical particle shape, the so-called first Kerker’s condition can be realized, at which the backward scattering practically vanishes for some combination of refractive index and particle size. However, realization of Kerker’s condition for spherical particles is only possible at the tail of the scattering resonances, when the particle scatters light weakly. Here we demonstrate that significantly higher forward scattering can be realized if spheroidal particles are considered instead. For each value of refractive index n exists an optimum shape of the particle, which produces minimum backscattering efficiency together with maximum forward scattering. This effect is achieved due to the overlapping of magnetic and electric dipole resonances of the spheroidal particle at th...
190 citations
TL;DR: In this paper, a method to tailor the reflection and scattering of terahertz (THz) waves in an anomalous manner by using 1-bit coding metamaterials is presented.
Abstract: Arbitrary control of terahertz (THz) waves remains a significant challenge although it promises many important applications. Here, a method to tailor the reflection and scattering of THz waves in an anomalous manner by using 1-bit coding metamaterials is presented. Specific coding sequences result in various THz far-field reflection and scattering patterns, ranging from a single beam to two, three, and numerous beams, which depart obviously from the ordinary Snell's law of reflection. By optimizing the coding sequences, a wideband THz thin film metamaterial with extremely low specular reflection, due to the scattering of the incident wave into various directions, is demonstrated. As a result, the reflection from a flat and flexible metamaterial can be nearly uniformly distributed in the half space with small intensity at each specific direction, manifesting a diffuse reflection from a rough surface. Both simulation and experimental results show that a reflectivity less than −10 dB is achieved over a wide frequency range from 0.8 to 1.4 THz, and it is insensitive to the polarization of the incident wave. This work reveals new opportunities arising from coding metamaterials in effective manipulation of THz wave propagation and may offer widespread applications.
180 citations
TL;DR: This work shows that the exceptionally bright white appearance of Cyphochilus and Lepidiota stigma beetles arises from a remarkably optimised anisotropy of intra-scale chitin networks, which act as a dense scattering media.
Abstract: Whiteness arises from diffuse and broadband reflection of light typically achieved through optical scattering in randomly structured media. In contrast to structural colour due to coherent scattering, white appearance generally requires a relatively thick system comprising randomly positioned high refractive-index scattering centres. Here, we show that the exceptionally bright white appearance of Cyphochilus and Lepidiota stigma beetles arises from a remarkably optimised anisotropy of intra-scale chitin networks, which act as a dense scattering media. Using time-resolved measurements, we show that light propagating in the scales of the beetles undergoes pronounced multiple scattering that is associated with the lowest transport mean free path reported to date for low-refractive-index systems. Our light transport investigation unveil high level of optimisation that achieves high-brightness white in a thin low-mass-per-unit-area anisotropic disordered nanostructure.
TL;DR: It is demonstrated that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution and is traced back to plasmon dissipation.
Abstract: Plasmon modes of the exact same individual gold nanoprisms are investigated through combined nanometer-resolved electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL) measurements. We show that CL only probes the radiative modes, in contrast to EELS, which additionally reveals dark modes. The combination of both techniques on the same particles thus provides complementary information and also demonstrates that although the radiative modes give rise to very similar spatial distributions when probed by EELS or CL, their resonant energies appear to be different. We trace this phenomenon back to plasmon dissipation, which affects in different ways the plasmon signatures probed by these techniques. Our experiments are in agreement with electromagnetic numerical simulations and can be further interpreted within the framework of a quasistatic analytical model. We therefore demonstrate that CL and EELS are closely related to optical scattering and extinction, respectively, with the addition of nanometer spatial resolution.
TL;DR: A prominent sector of nanotechnology is occupied by a class of carbon-based nanoparticles known as fullerenes, and there is a lack of adequate methodology for their size and shape characterisation, identification and quantitative detection in environmental and biological samples.
TL;DR: This study demonstrates the control of quantum tunneling in an ultracold lattice gas by the measurement backaction imposed by the act of imaging the atoms, i.e., light scattering, and sheds light on the implications of measurement on the coherent evolution of a quantum system.
Abstract: The process of measurement can modify the state of a quantum system and its subsequent evolution. Here, we demonstrate the control of quantum tunneling in an ultracold lattice gas by the measurement backaction imposed by the act of imaging the atoms, i.e., light scattering. By varying the rate of light scattering from the atomic ensemble, we show the crossover from the weak measurement regime, where position measurements have little influence on tunneling dynamics, to the strong measurement regime, where measurement-induced localization causes a large suppression of tunneling--a manifestation of the quantum Zeno effect. Our study realizes an experimental demonstration of the paradigmatic Heisenberg microscope and sheds light on the implications of measurement on the coherent evolution of a quantum system.
TL;DR: It is shown that the relaxational process causing the excess wing can also be detected by neutron scattering, which directly couples to density fluctuations.
Abstract: The relaxational dynamics in glass-forming glycerol and glycerol mixed with LiCl is investigated using different neutron scattering techniques. The performed neutron spin echo experiments, which extend up to relatively long relaxation time scales of the order of 10ns, should allow for the detection of contributions from the so-called excess wing. This phenomenon, whose microscopic origin is controversially discussed, arises in a variety of glass formers and, until now, was almost exclusively investigated by dielectric spectroscopy and light scattering. Here we show that the relaxational process causing the excess wing can also be detected by neutron scattering, which directly couples to density fluctuations.
TL;DR: This work demonstrates a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells, providing a simple route to approximately double the efficiency of NW-based solar cells.
Abstract: Semiconductor nanowires (NWs) often exhibit efficient, broadband light absorption despite their relatively small size. This characteristic originates from the subwavelength dimensions and high refractive indices of the NWs, which cause a light-trapping optical antenna effect. As a result, NWs could enable high-efficiency but low-cost solar cells using small volumes of expensive semiconductor material. Nevertheless, the extent to which the antenna effect can be leveraged in devices will largely determine the economic viability of NW-based solar cells. Here, we demonstrate a simple, low-cost, and scalable route to dramatically enhance the optical antenna effect in NW photovoltaic devices by coating the wires with conformal dielectric shells. Scattering and absorption measurements on Si NWs coated with shells of SiNx or SiOx exhibit a broadband enhancement of light absorption by ∼50–200% and light scattering by ∼200–1000%. The increased light–matter interaction leads to a ∼80% increase in short-circuit curre...
TL;DR: Simulations show that these semitransparent cells have similar spectrally averaged reflection and absorption in the CIGSe active layer as a Mo-based patterned cell, demonstrating that the absorption losses in the Mo can be partially turned into transmission through the semitranparent geometry.
Abstract: We experimentally demonstrate photocurrent enhancement in ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells with absorber layers of 460 nm by nanoscale dielectric light scattering patterns printed by substrate conformal imprint lithography. We show that patterning the front side of the device with TiO2 nanoparticle arrays results in a small photocurrent enhancement in almost the entire 400-1200 nm spectral range due to enhanced light coupling into the cell. Three-dimensional finite-difference time-domain simulations are in good agreement with external quantum efficiency measurements. Patterning the Mo/CIGSe back interface using SiO2 nanoparticles leads to strongly enhanced light trapping, increasing the efficiency from 11.1% for a flat to 12.3% for a patterned cell. Simulations show that optimizing the array geometry could further improve light trapping. Including nanoparticles at the Mo/CIGSe interface leads to substantially reduced parasitic absorption in the Mo back contact. Parasitic absorption in the back contact can be further reduced by fabricating CIGSe cells on top of a SiO2-patterned In2O3:Sn (ITO) back contact. Simulations show that these semitransparent cells have similar spectrally averaged reflection and absorption in the CIGSe active layer as a Mo-based patterned cell, demonstrating that the absorption losses in the Mo can be partially turned into transmission through the semitransparent geometry.
TL;DR: In this article, a light scattering layer that employs air voids (low-index scattering centers) embedded in a high-index polyimide matrix to effectively frustrate the substrate-trapped light, increasing the outcoupling efficiency was developed.
Abstract: Despite high internal quantum efficiencies, planar organic light-emitting diodes (OLEDs) typically suffer from limited outcoupling efficiencies. To improve this outcoupling efficiency, we have developed a new thin (∼2 μm) light scattering layer that employs air voids (low-index scattering centers) embedded in a high-index polyimide matrix to effectively frustrate the substrate-trapped light, increasing the outcoupling efficiency. The porous polyimide scattering layers are created through the simple and scalable fabrication technique of phase inversion. The optical properties of the scattering layers have been characterized via microscopy, transmittance/haze measurements, and ellipsometry, which demonstrate the excellent scattering properties of these layers. We have integrated these films into a green OLED stack, where they show a 65% enhancement of the external quantum efficiency and a 77% enhancement of the power efficiency. Furthermore, we have integrated these layers into a white OLED and observed sim...
TL;DR: The flexible tunability of the Fano resonance by particle morphology opens up the possibility of tailoring the optical scattering force accordingly, offering an additional degree of freedom to optical selection and sorting of plasmonic nanoparticles.
Abstract: We demonstrate theoretically that Fano resonance can induce a negative optical scattering force acting on plasmonic nanoparticles in the visible light spectrum when an appropriate manipulating laser beam is adopted. Under the illumination of a zeroth-order Bessel beam, the plasmonic nanoparticle at its Fano resonance exhibits a much stronger forward scattering than backward scattering and consequently leads to a net longitudinal backward optical scattering force, termed Fano resonance-induced negative optical scattering force. The extinction spectra obtained based on the Mie theory show that the Fano resonance arises from the interference of simultaneously excited multipoles, which can be either a broad electric dipole mode and a narrow electric quadrupole mode, or a quadrupole and an octupole mode mediated by the broad electric dipole. Such Fano resonance-induced negative optical scattering force is demonstrated to occur for core–shell, homogeneous, and hollow metallic particles and can therefore be expe...
TL;DR: It is demonstrated that single-beam laser trapping can be used to induce and quantify the local refrigeration of physiological media by >10 °C following the emission of photoluminescence from upconverting yttrium lithium fluoride (YLF) nanocrystals.
Abstract: Coherent laser radiation has enabled many scientific and technological breakthroughs including Bose–Einstein condensates, ultrafast spectroscopy, superresolution optical microscopy, photothermal therapy, and long-distance telecommunications. However, it has remained a challenge to refrigerate liquid media (including physiological buffers) during laser illumination due to significant background solvent absorption and the rapid (∼ps) nonradiative vibrational relaxation of molecular electronic excited states. Here we demonstrate that single-beam laser trapping can be used to induce and quantify the local refrigeration of physiological media by >10 °C following the emission of photoluminescence from upconverting yttrium lithium fluoride (YLF) nanocrystals. A simple, low-cost hydrothermal approach is used to synthesize polycrystalline particles with sizes ranging from 1 μm. A tunable, near-infrared continuous-wave laser is used to optically trap individual YLF crystals with an irradiance on the order of 1 MW/cm2. Heat is transported out of the crystal lattice (across the solid–liquid interface) by anti-Stokes (blue-shifted) photons following upconversion of Yb3+ electronic excited states mediated by the absorption of optical phonons. Temperatures are quantified through analysis of the cold Brownian dynamics of individual nanocrystals in an inhomogeneous temperature field via forward light scattering in the back focal plane. The cold Brownian motion (CBM) analysis of individual YLF crystals indicates local cooling by >21 °C below ambient conditions in D2O, suggesting a range of potential future applications including single-molecule biophysics and integrated photonic, electronic, and microfluidic devices.
TL;DR: These results will be important not only for applications of light emitting devices, solar cells, optical filters, and various surface enhanced spectroscopies but also for furthering the understanding on the light-matter interactions at the nanoscale.
Abstract: Steering incident light into specific directions at the nanoscale is very important for future nanophotonics applications of signal transmission and detection. A prerequisite for such a purpose is the development of nanostructures with high-efficiency unidirectional light scattering properties. Here, from both theoretical and experimental sides, we conceived and demonstrated the unidirectional visible light scattering behaviors of a heterostructure, Janus dimer composed of gold and silicon nanospheres. By carefully adjusting the sizes and spacings of the two nanospheres, the Janus dimer can support both electric and magnetic dipole modes with spectral overlaps and comparable strengths. The interference of these two modes gives rise to the narrow-band unidirectional scattering behaviors with enhanced forward scattering and suppressed backward scattering. The directionality can further be improved by arranging the dimers into one-dimensional chain structures. In addition, the dimers also show remarkable ele...
TL;DR: Moderate-refractive-index dielectric nano-spheres are found to possess strong electric and magnetic dipole resonances in the visible region and exhibit directional forward scattering at the strongest scattering peak.
Abstract: Moderate-refractive-index dielectric nano-spheres are found to possess strong electric and magnetic dipole resonances in the visible region. Owing to the overlap of the electric and magnetic dipole resonances, moderate-refractive-index dielectric nanospheres exhibit directional forward scattering at the strongest scattering peak. Such directional scattering is experimentally observed on colloidal Cu2O nanospheres, which are readily prepared through wet-chemistry methods.
TL;DR: It is demonstrated that the suppression of light scattering for any direction of observation can be achieved for a uniform dielectric object with high refractive index, in a sharp contrast to the cloaking with multilayered plasmonic structures suggested previously.
Abstract: Subwavelength structures demonstrate many unusual optical properties which can be employed for engineering of a new generation of functional metadevices, as well as controlled scattering of light and invisibility cloaking. Here we demonstrate that the suppression of light scattering for any direction of observation can be achieved for a uniform dielectric object with high refractive index, in a sharp contrast to the cloaking with multilayered plasmonic structures suggested previously. Our finding is based on the novel physics of cascades of Fano resonances observed in the Mie scattering from a homogeneous dielectric rod. We observe this effect experimentally at microwaves by employing high temperature-dependent dielectric permittivity of a glass cylinder with heated water. Our results open a new avenue in analyzing the optical response of high-index dielectric nanoparticles and the physics of cloaking.
TL;DR: In this article, it was shown that breaking the symmetry of an all-dielectric nanoparticle leads to a geometrically tunable magnetoelectric coupling, i.e., an omega-type bianisotropy.
Abstract: The study of high-index dielectric nanoparticles currently attracts a lot of attention. They do not suffer from absorption but promise to provide control of the properties of light comparable to plasmonic nanoparticles. To further advance the field, it is important to identify versatile dielectric nanoparticles with unconventional properties. Here, we show that breaking the symmetry of an all-dielectric nanoparticle leads to a geometrically tunable magnetoelectric coupling, i.e., an omega-type bianisotropy. The suggested nanoparticle exhibits different backscatterings and, as an interesting consequence, different optical scattering forces for opposite illumination directions. An array of such nanoparticles provides different reflection phases when illuminated from opposite directions. With a proper geometrical tuning, this bianisotropic nanoparticle is capable of providing a $2\ensuremath{\pi}$ phase change in the reflection spectrum while possessing a rather large and constant amplitude. This allows the creation of reflectarrays with near-perfect transmission out of the resonance band due to the absence of a usually employed metallic screen.
TL;DR: In this paper, the authors explored the sensitivity of the reported coating properties to the assumed values of density and refractive index of the core that are used in these calculations, which can greatly affect the reported parameters such as coating thickness.
Abstract: . Black carbon (BC) is the dominant absorbing aerosol in the atmosphere, and plays an important role in climate and human health. The optical properties and cloud condensation nuclei (CCN) activity of soot depend on the amounts (both relative and absolute) of BC and non-refractory material in the particles. Mixing between these two components is often represented in models by a core / shell coated sphere. The single-particle soot photometer (SP2) is one of, if not the only, instrument capable of reporting distributions of both core size and coating thickness. Most studies combine the SP2's incandescence and 1064 nm scattering data to report coating properties, but to date there is no consistency in the assumed values of density and refractive index of the core that are used in these calculations, which can greatly affect the reported parameters such as coating thickness. Given that such data are providing an important constraint for model comparisons and comparison between large data sets, it is important that this lack of consistency is addressed. In this study we explore the sensitivity of the reported coatings to these parameters. An assessment of the coating properties of freshly emitted, thermodenuded ambient particles demonstrated that a core density of 1.8 g cm−3 and refractive index of (2.26–1.26i) were the most appropriate to use with ambient soot in the Los Angeles area. Using these parameters generated a distribution with median shell / core ratio of 1.02 ± 0.11, corresponding to a median absolute coating thickness of 2 ± 8 nm. The main source of statistical error in the single-particle data was random variation in the incandescence signals. Other than the sensitivity to core refractive index, the incandescence calibration was the main source of uncertainty when optically determining the average coatings. The refractive index of coatings was found to have only a minor influence. This work demonstrates that using this technique the SP2 can accurately determine the average mixing state (externally or internally mixed) of ambient soot within the precision of the instrument calibration. Ambient coatings were measured up to a median shell / core ratio of 1.50 ± 0.11, meaning that this technique is able to resolve absolute changes in mixing state. However, when different core parameters were used, the core / shell ratio and the coating thickness were shown to be offset by amounts that could be larger than the atmospheric variability in these parameters, though the results have a similar precision. For comparison, using the core parameters that resulted in the thickest coatings, on the same thermodenuded fresh particles as before, generated a median shell / core ratio of 1.39 ± 0.11, corresponding to a median absolute coating thickness of 30 ± 8 nm. These results must be taken into account when comparing BC coatings measured using this technique, or if using these data for optical or CCN calculations. We have determined the most appropriate values of BC density and refractive index to use to measure mixing state at 1064 nm where particle morphology has only a minor effect, but appropriate values to use for optical calculations of nonspherical particles at visible wavelengths will also be subject to similar, significant uncertainties. Without similar constraints as those provided here, constraining the behaviour of BC particles in models using field data will be subject to large systematic measurement uncertainties.
TL;DR: In this article, the authors measured the quasi-Beer-Lambert properties of photopolymerizable ceramic suspensions and determined the depth and width attenuation and the critical energy doses for a given energy dose.
Abstract: Light scattering in photopolymerizable ceramic suspensions affects the resolution of photopolymerization processing methods; it is necessary to predict the cure width and cure depth at a given energy dose for a suspension with a known composition. The volume fraction of ceramic powder in the suspension or the refractive index (RI) contrast between the ceramic powder and the liquid solution was varied, measuring the quasi-Beer–Lambert suspension properties. For these suspensions, the depth and width attenuation and the depth and width critical energy doses were determined. The volume fraction of powder has no effect on the broadening depth; the solids loading can be varied without concern for increased scattering within the suspension. The broadening depth decreases with the logarithm of RI contrast. Suspensions with a small RI contrast are able to cure deep, narrow features without broadening.
TL;DR: In this article, the authors investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes and show that volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances significantly modify the propagation of thermally activated GHz phonons.
Abstract: We investigate experimentally and theoretically the acoustic phonon propagation in two-dimensional phononic crystal membranes. Solid-air and solid-solid phononic crystals were made of square lattices of holes and Au pillars in and on 250 nm thick single crystalline Si membrane, respectively. The hypersonic phonon dispersion was investigated using Brillouin light scattering. Volume reduction (holes) or mass loading (pillars) accompanied with second-order periodicity and local resonances are shown to significantly modify the propagation of thermally activated GHz phonons. We use numerical modeling based on the finite element method to analyze the experimental results and determine polarization, symmetry, or three-dimensional localization of observed modes.
TL;DR: A parametric study of the optical properties of disk-shaped gap-surface plasmon (GSP) resonators, consisting of a glass spacer sandwiched between two gold disks, with numerical calculations that corroborate the conditions derived from the multipole expansion.
Abstract: Starting from a general description of light scattering by a nanoparticle in homogeneous surroundings and situated near a substrate, we outline the connection to multipole expansion of scattered light and derive conditions and limits on achievable half-space scattering asymmetry, including the possibility of unidirectional scattering along the propagation direction of the incident light (i.e., generalized Kerker conditions). As a way of realizing strongly asymmetric scattering, we perform a parametric study of the optical properties of disk-shaped gap-surface plasmon (GSP) resonators, consisting of a glass spacer sandwiched between two gold disks, with numerical calculations that corroborate the conditions derived from the multipole expansion. Finally, we present proof-of-principle experiments of asymmetric scattering by GSP-resonators on a glass substrate.
TL;DR: The presented numerical methods can be used to compute the hadronic light-by-light contribution to the anomalous magnetic moment of the muon.
Abstract: We perform a lattice QCD calculation of the hadronic light-by-light scattering amplitude in a broad kinematical range. At forward kinematics, the results are compared to a phenomenological analysis based on dispersive sum rules for light-by-light scattering. The size of the pion pole contribution is investigated for momenta of typical hadronic size. The presented numerical methods can be used to compute the hadronic light-by-light contribution to the anomalous magnetic moment of the muon. Our calculations are carried out in two-flavor QCD with the pion mass in the range of 270-450 MeV and contain so far only the diagrams with fully connected quark lines.
TL;DR: It is shown that the motion-induced degradation of the OPC turbidity-suppression effect through a dynamic scattering medium shares the same decorrelation time constant as that determined from speckle intensity autocorrelation - a popular conventional measure of scatterer movement.
Abstract: Light scattering in biological tissue significantly limits the accessible depth for localized optical interrogation and deep-tissue optical imaging. This challenge can be overcome by exploiting the time-reversal property of optical phase conjugation (OPC) to reverse multiple scattering events or suppress turbidity. However, in living tissue, scatterers are highly movable and the movement can disrupt time-reversal symmetry when there is a latency in the OPC playback. In this paper, we show that the motion-induced degradation of the OPC turbidity-suppression effect through a dynamic scattering medium shares the same decorrelation time constant as that determined from speckle intensity autocorrelation – a popular conventional measure of scatterer movement. We investigated this decorrelation characteristic time through a 1.5-mm-thick dorsal skin flap of a living mouse and found that it ranges from 50 ms to 2.5 s depending on the level of immobilization. This study provides information on relevant time scales for applying OPC to living tissues.