Showing papers on "Scattering published in 2011"

Resonant Inelastic X-ray Scattering Studies of Elementary Excitations

Abstract: Resonant Inelastic X-ray Scattering (RIXS) is an X-ray in, X-ray out technique that enables one to study the dispersion of excitations in solids. In this thesis, we investigated how various elementary excitations of transition metal oxides show up in RIXS spectra.

PT-symmetry breaking and laser-absorber modes in optical scattering systems.

Abstract: Using a scattering matrix formalism, we derive the general scattering properties of optical structures that are symmetric under a combination of parity and time reversal (PT). We demonstrate the existence of a transition between PT-symmetric scattering eigenstates, which are norm preserving, and symmetry-broken pairs of eigenstates exhibiting net amplification and loss. The system proposed by Longhi [Phys. Rev. A 82, 031801 (2010).], which can act simultaneously as a laser and coherent perfect absorber, occurs at discrete points in the broken-symmetry phase, when a pole and zero of the S matrix coincide.

Dynamic Light Scattering: Applications of Photon Correlation Spectroscopy

Abstract: 1 Introduction.- References.- 2 Light Scattering Apparatus.- 2.1. Introduction.- 2.2. Electromagnetic Waves.- 2.3. Light Scattering.- 2.3.1. Background.- 2.3.2. Fluctuations.- 2.3.3. The Coherence Area.- 2.3.4. Time Dependence.- 2.3.5. Local Oscillator.- 2.4. The Light Scattering Experiment.- 2.4.1. Introduction.- 2.4.2. The Light Source.- 2.4.3. The Spectrometer.- 2.4.4. The Detector.- 2.4.5. Signal Analyzers.- 2.5. Signal-to-Noise Ratio.- 2.5.1. Introduction.- 2.5.2. Effects due to Finite Intensity.- 2.5.3. Effects due to Finite Experiment Duration.- 2.5.4. Effects due to Unwanted Scattered Light.- 2.6. Data Analysis.- 2.6.1. Introduction.- 2.6.2. Selecting the Theoretical Form.- 2.6.3. Use of the ?2Test.- 2.6.4. Summary of Possible Forms.- 2.6.5. Polydispersity.- 2.7. Special Apparatus.- 2.7.1. Electrophoretic Light Scattering.- 2.7.2. Fabry-Perot Interferometers.- 2.7.3. Software Correlators.- 2.7.4. Cross-Correlation Experiment.- 2.8. Conclusions.- References and Notes.- 3 Dynamic Depolarized Light Scattering.- 3.1. Introduction.- 3.2. Principles of Depolarized Scattering.- 3.2.1. Scattering Configurations.- 3.2.2. Physical Principles.- 3.3 Rigid Macromolecules in Dilute Solution.- 3.3.1. Hydrodynamics of Rigid Macromolecules.- 3.3.2. Interferometric Studies.- 3.3.3. Photon Correlation Studies.- 3.4. Rod-Shaped Macromolecules in Semidilute Solutions.- 3.5. Flexible Macromolecules.- 3.6. Rotation of Small Molecules in Viscous Media.- 3.7. Resonance-Enhanced Depolarized Dynamic Light.- Scattering.- References and Notes.- 4 Particle Interactions.- 4.1. Introduction.- 4.2. Quantities Measured by Light Scattering.- 4.2.1. Introduction.- 4.2.2. Monodisperse Systems.- 4.2.3. Polydisperse Systems.- 4.2.4. Discussion.- 4.3.Theory.- 4.3.1. Introduction.- 4.3.2. Stokes-Einstein Relations.- 4.3.3. The Generalized Smoluchowski Equation.- 4.3.4. Hydrodynamic Interactions.- 4.3.5. Short-Time Motions.- 4.3.6. Projection Operator Analysis.- 4.3.7. Dynamics in the Small-q Limit-Cooperative and Self-Diffusion.- 4.4. Charged Particles in Dilute Suspension (Negligible Hydrodynamic Interactions).- 4.4.1. Introduction.- 4.4.2. Single-Particle Motions.- 4.4.3. The First Cumulant.- 4.4.4. Low-g Limit and the Effect of Polydispersity.- 4.4.5. Memory Effects.- 4.5. Effects of Hydrodynamic Interactions.- 4.5.1. Introduction.- 4.5.2. Theory of the Collective Diffusion Coefficient in the Hydrodynamic Regime.- 4.5.3. Experimental Results.- 4.5.4. Microemulsions.- 4.5.5. Hydrodynamic Effects at Finite q.- 4.6. Small-Ion Effects.- 4.7. Conclusions.- 4.8. Addendum.- References and Notes.- 5 Quasielastic Light Scattering from Dilute and Semidilute Polymer Solution.- 5.1. Introduction.- 5.2.The Single Chain.- 5.2.1. Basic Polymer Statistics.- 5.2.2. Dynamical Regimes.- 5.2.3. Center-of-Mass Diffusion (q R 1).- 5.2.4. Internal Dynamics and the Dynamic Structure Factor.- 5.3. Virial Regime.- 5.4. Semidilute Solutions.- 5.4.1. Introduction.- 5.4.2. Dynamical Regimes.- 5.4.3. Conclusions.- References.- 6Dynamic Light Scattering in Bulk Polymers.- 6.1. Introduction.- 6.2. Light Scattering.- 6.3. Sources of Light Scattering.- 6.4. Theory.- 6.5. Applications.- 6.5.1. Brillouin Spectroscopy.- 6.5.2. Dynamic Central Peaks.- 6.5.3. Depolarized Rayleigh Scattering.- 6.6. Conclusions.- References.- 7 Critical Phenomena.- 7.1. Introduction.- 7.2. Critical Fluctuations.- 7.2.1. Static Critical Behavior.- 7.2.2. Dynamic Critical Behavior.- 7.3. Depolarized Rayleigh Scattering.- 7.4 .Entropy Fluctuations.- 7.4.1. Entropy Rayleigh Factor.- 7.4.2. Local Entropy Fluctuations.- 7.5. Multicomponent Fluids.- 7.5.1. Ternary Liquid Mixtures.- 7.5.2. Binary Fluid in the Presence of Isotope Exchange...- 7.5.3. Tricritical Point Behavior.- 7.6. Spinodal Decomposition and Critical Behavior Induced by Shear Flow.- 7.6.1. Spinodal Decomposition.- 7.6.2. Critical Behavior Induced by Shear Flow.- References.- 8 Laser Light Scattering in Micellar Systems.- 8.1. Introduction.- 8.2. Theoretical Aspects of Deducing Micellar Size, Polydispersity, and Shape.- 8.3. Applications of Laser Light Scattering to Micellar Systems.- 8.3.1. Aqueous Synthetic Detergent Systems.- 8.3.2. Biological Micelles.- 8.3.3. Microemulsion and Inverted Micellar Systems.- 8.4. Summary.- References.- 9Light Scattering from Polymer Gels.- 9.1. Introduction.- 9.2. Collective Modes in Gels.- 9.2.1. Collective Diffusion in a Gel.- 9.2.2. Comparison between Diffusion of Polymers and Gels.- 9.2.3. Light Scattering from Collective Diffusion Modes in aGel.- 9.2.4. Comparison between Light Scattering and Swelling of Gels.- 9.3. Kirkwood-Risemann-Type Expression of Diffusion Coefficient.- 9.3.1. Gels in Good Solvent.- 9.3.2. Light Scattering from Gels in Good Solvents.- 9.4. Phase Transition in Gels.- 9.5. Conclusion.- References.- 10 Biological Applications.- 10.1. Introduction.- 10.2. Physical Principles of Quasielastic Light Scattering.- 10.2.1. Autocorrelation Function.- 10.2.2. Power Spectrum.- 10.2.3. Translational Diffusion.- 10.2.4. Uniform Translational Motion.- 10.2.5. Rotational and Internal Motions.- 10.2.6. Number Fluctuations.- 10.2.7. Transport Coefficients and Molecular Structure.- 10.3. Instrumentation and Data Analysis.- 10.3.1. Instrumentation.- 10.3.2. Polydispersity.- 10.3.3. Concentration Effects.- 10.3.4. Charge Effects.- 10.4. Macromolecular Characterization and Interactions.- 10.4.1. Proteins.- 10.4.2. NucleicAcids.- 10.4.3. Viruses.- 10.4.4. Polysaccharides and Proteoglycans.- 10.4.5. Vesicles and Protein-Membrane Complexes.- 10.4.6. Micelles.- 10.5. Physiological and Biomedical Applications.- 10.5.1. Cataracts.- 10.5.2. Immunoassay.- 10.5.3. CellSurfaces.- 10.5.4. Monolayers, Films, and Membranes.- 10.5.5. Gels and Entangled Solutions.- 10.5.6. Muscle.- 10.5.7. Biological Velocimetry.- 10.5.8. Motility.- 10.6. Conclusion.- References.

Controlling inelastic light scattering quantum pathways in graphene

Abstract: Inelastic light scattering spectroscopy has, since its first discovery, been an indispensable tool in physical science for probing elementary excitations, such as phonons, magnons and plasmons in both bulk and nanoscale materials. In the quantum mechanical picture of inelastic light scattering, incident photons first excite a set of intermediate electronic states, which then generate crystal elementary excitations and radiate energy-shifted photons. The intermediate electronic excitations therefore have a crucial role as quantum pathways in inelastic light scattering, and this is exemplified by resonant Raman scattering and Raman interference. The ability to control these excitation pathways can open up new opportunities to probe, manipulate and utilize inelastic light scattering. Here we achieve excitation pathway control in graphene with electrostatic doping. Our study reveals quantum interference between different Raman pathways in graphene: when some of the pathways are blocked, the one-phonon Raman intensity does not diminish, as commonly expected, but increases dramatically. This discovery sheds new light on the understanding of resonance Raman scattering in graphene. In addition, we demonstrate hot-electron luminescence in graphene as the Fermi energy approaches half the laser excitation energy. This hot luminescence, which is another form of inelastic light scattering, results from excited-state relaxation channels that become available only in heavily doped graphene.

Time-reversed ultrasonically encoded optical focusing into scattering media.

Abstract: Light focusing plays a central role in biomedical imaging, manipulation and therapy. In scattering media, direct light focusing becomes infeasible beyond one transport mean free path. All previous methods used to overcome this diffusion limit lack a practical internal ‘guide star’. Here, we propose and experimentally validate a novel concept called time-reversed ultrasonically encoded (TRUE) optical focusing to deliver light into any dynamically defined location inside a scattering medium. First, diffused coherent light is encoded by a focused ultrasonic wave to provide a virtual internal guide star. Only the encoded light is time-reversed and transmitted back to the ultrasonic focus. The time-reversed ultrasonically encoded optical focus—defined by the ultrasonic wave—is unaffected by multiple scattering of light. Such focusing is particularly desirable in biological tissue, where ultrasonic scattering is ~1,000 times weaker than optical scattering. Various fields, including biomedical and colloidal optics, can benefit from TRUE optical focusing.

Focusing and compression of ultrashort pulses through scattering media

Abstract: Scientists show that spatiotemporal focusing and compression of non-Fourier-limited pulses through scattering media can be achieved by manipulating only the spatial degrees of freedom of the incident wavefront. This technique is potentially attractive for optical manipulation and nonlinear imaging in scattering media.

Four-Component Scattering Power Decomposition With Rotation of Coherency Matrix

Abstract: This paper presents an improvement to a decomposition scheme for the accurate classification of polarimetric synthetic aperture radar (POLSAR) images. Using a rotation of the coherency matrix to minimize the cross-polarized component, the four-component scattering power decomposition is applied to fully polarimetric SAR images. It is known that oriented urban area and vegetation signatures are decomposed into the same volume scattering mechanism in the previous decompositions and that it is difficult to distinguish vegetation from oblique urban areas with respect to the radar direction of illumination within the volume scattering mechanism. It is desirable to distinguish these two scattering mechanisms for accurate classification although they exhibit similar polarimetric responses. The new decomposition scheme by implementing a rotation of the coherency matrix first and, subsequently, the four-component decomposition yields considerably improved accurate results that oriented urban areas are recognized as double bounce objects from volume scattering.

Theory of double-resonant Raman spectra in graphene: Intensity and line shape of defect-induced and two-phonon bands

Abstract: We calculate the double resonant (DR) Raman spectrum of graphene, and determine the lines associated to both phonon-defect processes, and two-phonons ones. Phonon and electronic dispersions reproduce calculations based on density functional theory corrected with GW. Electron-light, -phonon, and -defect scattering matrix elements and the electronic linewidth are explicitly calculated. Defect-induced processes are simulated by considering different kind of idealized defects. For an excitation energy of $\epsilon_L=2.4$ eV, the agreement with measurements is very good and calculations reproduce: the relative intensities among phonon-defect or among two-phonon lines; the measured small widths of the D, $D'$, 2D and $2D'$ lines; the line shapes; the presence of small intensity lines in the 1800, 2000 cm$^{-1}$ range. We determine how the spectra depend on the excitation energy, on the light polarization, on the electronic linewidth, on the kind of defects and on their concentration. According to the present findings, the intensity ratio between the $2D'$ and 2D lines can be used to determine experimentally the electronic linewidth. The intensity ratio between the $D$ and $D'$ lines depends on the kind of model defect, suggesting that this ratio could possibly be used to identify the kind of defects present in actual samples. Charged impurities outside the graphene plane provide an almost undetectable contribution to the Raman signal.

Reduction in the Thermal Conductivity of Single Crystalline Silicon by Phononic Crystal Patterning

Abstract: Phononic crystals (PnCs) are the acoustic wave equivalent of photonic crystals, where a periodic array of scattering inclusions located in a homogeneous host material causes certain frequencies to be completely reflected by the structure. In conjunction with creating a phononic band gap, anomalous dispersion accompanied by a large reduction in phonon group velocities can lead to a massive reduction in silicon thermal conductivity. We measured the cross plane thermal conductivity of a series of single crystalline silicon PnCs using time domain thermoreflectance. The measured values are over an order of magnitude lower than those obtained for bulk Si (from 148 W m(-1) K(-1) to as low as 6.8 W m(-1) K(-1)). The measured thermal conductivity is much smaller than that predicted by only accounting for boundary scattering at the interfaces of the PnC lattice, indicating that coherent phononic effects are causing an additional reduction to the cross plane thermal conductivity.

A multiple sphere T-matrix Fortran code for use on parallel computer clusters

Abstract: A general-purpose Fortran-90 code for calculation of the electromagnetic scattering and absorption properties of multiple sphere clusters is described. The code can calculate the efficiency factors and scattering matrix elements of the cluster for either fixed or random orientation with respect to the incident beam and for plane wave or localized- approximation Gaussian incident fields. In addition, the code can calculate maps of the electric field both interior and exterior to the spheres.The code is written with message passing interface instructions to enable the use on distributed memory compute clusters, and for such platforms the code can make feasible the calculation of absorption, scattering, and general EM characteristics of systems containing several thousand spheres.

Role of Disorder and Anharmonicity in the Thermal Conductivity of Silicon-Germanium Alloys: A First-Principles Study

Abstract: The thermal conductivity of disordered silicon-germanium alloys is computed from density-functional perturbation theory and with relaxation times that include both harmonic and anharmonic scattering terms. We show that this approach yields an excellent agreement at all compositions with experimental results and provides clear design rules for the engineering of nanostructured thermoelectrics. For Si(x)Ge(1-x), more than 50% of the heat is carried at room temperature by phonons of mean free path greater than 1 mu m, and an addition of as little as 12% Ge is sufficient to reduce the thermal conductivity to the minimum value achievable through alloying. Intriguingly, mass disorder is found to increase the anharmonic scattering of phonons through a modification of their vibration eigenmodes, resulting in an increase of 15% in thermal resistivity.

R-Matrix Theory of Atomic Collisions: Application to Atomic, Molecular and Optical Processes

Abstract: Part I - Collision Theory.- Potential Scattering.- Multichannel Collision Theory.- Resonances and Threshold Behaviour.- Part II - R-matrix Theory and Applications.- Introduction to R-matrix Theorie: Potential Scattering.- Electron Collisions with Atoms and Ions.- Intermediate Energy Collision.- Positron Collisions with Atoms and Ions.- Photoionization, Photorecombination and Atoms in Fields.- Multiphoton Processes: Floquet Theory.- Multiphoton Processes: Time-Dependent Theory.- Collisions with Molecules.- Electron Interactions in Solids

Multipole light scattering by nonspherical nanoparticles in the discrete dipole approximation

Abstract: In the framework of the discrete dipole approximation we develop a theoretical approach that allows the analysis of the role of multipole modes in the extinction and scattering spectra of arbitrary shaped nanoparticles. The main attention is given to the first multipoles including magnetic dipole and electric quadrupole moments. The role of magnetic quadrupole and electric octupole modes is also discussed. The method is applied to nonspherical Si nanoparticles with resonant multipole responses in the visible optical range, allowing a decomposition of single extinction (scattering) peaks into their constituent multipole contributions. It is shown by numerical simulations that it is possible to design silicon particles for which the electric dipole and magnetic dipole resonances are located at the same wavelength under certain propagation directions of incident light, providing new possibilities in metamaterial developments.

Electrically tunable surface-to-bulk coherent coupling in topological insulator thin films

Abstract: We study coherent electronic transport in charge-density-tunable microdevices patterned from thin films of the topological insulator (TI) Bi${}_{2}$Se${}_{3}$. The devices exhibit pronounced electric field effect, including ambipolar modulation of the resistance with an on-and-off ratio of 500%. We show that the weak antilocalization correction to conductance is sensitive to the number of coherently coupled channels, which in a TI includes the top and bottom surfaces and the bulk carriers. These are separated into coherently independent channels by the application of gate voltage and at elevated temperatures. Our results are consistent with a model where channel separation is determined by a competition between the phase coherence time and the surface-to-bulk scattering time.

Overcoming the diffraction limit using multiple light scattering in a highly disordered medium.

Abstract: We report that disordered media made of randomly distributed nanoparticles can be used to overcome the diffraction limit of a conventional imaging system. By developing a method to extract the original image information from the multiple scattering induced by the turbid media, we dramatically increase a numerical aperture of the imaging system. As a result, the resolution is enhanced by more than 5 times over the diffraction limit, and the field of view is extended over the physical area of the camera. Our technique lays the foundation to use a turbid medium as a far-field superlens.

Strain-dependent splitting of the double-resonance Raman scattering band in graphene.

Abstract: Under homogeneous uniaxial strains, the Raman $2D$ band of graphene involving two-phonon double-resonance scattering processes splits into two peaks and they altogether redshift strongly depending on the direction and magnitude of the strain. Through polarized micro-Raman measurements and first-principles calculations, the effects are shown to originate from significant changes in resonant conditions owing to both the distorted Dirac cones and anisotropic modifications of phonon dispersion under uniaxial strains. Quantitative agreements between the calculation and experiment enable us to determine the dominant double-resonance Raman scattering path, thereby answering a fundamental question concerning this key experimental analyzing tool for graphitic systems.

Scattering lens resolves sub-100 nm structures with visible light.

Abstract: The smallest structures that conventional lenses are able to optically resolve are of the order of 200 nm. We introduce a new type of lens that exploits multiple scattering of light to generate a scanning nanosized optical focus. With an experimental realization of this lens in gallium phosphide we imaged gold nanoparticles at 97 nm optical resolution. Our work is the first lens that provides a resolution better than 100 nm at visible wavelengths.

Role of Disorder and Anharmonicity in the Thermal Conductivity of Silicon-Germanium Alloys: A First-Principles Study

Abstract: The thermal conductivity of disordered silicon-germanium alloys is computed from density-functional perturbation theory and with relaxation times that include both harmonic and anharmonic scattering terms. We show that this approach yields an excellent agreement at all compositions with experimental results and provides clear design rules for the engineering of nanostructured thermoelectrics. For Si(x)Ge(1-x), more than 50% of the heat is carried at room temperature by phonons of mean free path greater than 1 mu m, and an addition of as little as 12% Ge is sufficient to reduce the thermal conductivity to the minimum value achievable through alloying. Intriguingly, mass disorder is found to increase the anharmonic scattering of phonons through a modification of their vibration eigenmodes, resulting in an increase of 15% in thermal resistivity.

Raman 2D-Band Splitting in Graphene: Theory and Experiment

Abstract: We present a systematic experimental and theoretical study of the two-phonon (2D) Raman scattering in graphene under uniaxial tension. The external perturbation unveils that the 2D mode excited with 785 nm has a complex line-shape mainly due to the contribution of two distinct double resonance scattering processes (inner and outer) in the Raman signal. The splitting depends on the direction of the applied strain and the polarization of the incident light. The results give new insight into the nature of the 2D band and have significant implications for the use of graphene as reinforcement in composites since the 2D mode is crucial to assess how effectively graphene uptakes an applied stress or strain.

Microscopic theory of absorption and ultrafast many-particle kinetics in graphene

Abstract: We investigate the relaxation kinetics of optically excited charge carriers in graphene focusing on the time-, momentum-, and angle-resolved interplay between carrier-carrier and carrier-phonon scattering channels. To benchmark the theoretical approach, we first discuss the linear absorption spectrum of graphene. In agreement with recent experimental results, our calculations reveal: (i) a pronounced excitonic effect at the saddle point, (ii) a constant absorbance in the visible region, and (iii) a drop-off for energies close to the Dirac point. After a nonlinear optical excitation, we observe that $\ensuremath{\Gamma}$-LO phonons efficiently and quickly redistribute the initially highly anisotropic nonequilibrium carrier distribution. In contrast, Coulomb-induced carrier relaxation is preferably carried out directly toward the Dirac point leading to an ultrafast thermalization of the carrier system. We evaluate the temporal dynamics of optical and acoustic phonons and discuss the energy dissipation arising from phonon-induced intra- and interband scattering. Furthermore, we investigate the influence of diagonal and off-diagonal many-particle dephasing on the ultrafast carrier relaxation dynamics. The gained insights contribute to a better microscopic understanding of optical and electronic properties of graphene.

Search for a new gauge boson in electron-nucleus fixed-target scattering by the APEX experiment.

Abstract: We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces.

Insight into asphaltene nanoaggregate structure inferred by small angle neutron and X-ray scattering.

Abstract: Complementary neutron and X-ray small angle scattering results give prominent information on the asphaltene nanostructure. Precise SANS and SAXS measurements on a large q-scale were performed on the same dilute asphaltene–toluene solution, and absolute intensity scaling was carried out. Direct comparison of neutron and X-ray spectra enables description of a fractal organization made from the aggregation of small entities of 16 kDa, exhibiting an internal fine structure. Neutron contrast variation experiments enhance the description of this nanoaggregate in terms of core–shell disk organization, giving insight into core and shell dimensions and chemical compositions. The nanoaggregates are best described by a disk of total radius 32 A with 30% polydispersity and a height of 6.7 A. Composition and density calculations show that the core is a dense and aromatic structure, contrary to the shell, which is highly aliphatic. These results show a good agreement with the general view of the Yen model (Yen, T. F.; ...

Quantum simulation of the Klein paradox with trapped ions.

Abstract: We report on quantum simulations of relativistic scattering dynamics using trapped ions. The simulated state of a scattering particle is encoded in both the electronic and vibrational state of an ion, representing the discrete and continuous components of relativistic wave functions. Multiple laser fields and an auxiliary ion simulate the dynamics generated by the Dirac equation in the presence of a scattering potential. Measurement and reconstruction of the particle wave packet enables a frame-by-frame visualization of the scattering processes. By precisely engineering a range of external potentials we are able to simulate text book relativistic scattering experiments and study Klein tunneling in an analogue quantum simulator. We describe extensions to solve problems that are beyond current classical computing capabilities.

Angle-suppressed scattering and optical forces on submicrometer dielectric particles.

Abstract: We show that submicrometer silicon spheres, whose polarizabilities are completely given by their two first Mie coefficients, are an excellent laboratory to test effects of both angle-suppressed and resonant differential scattering cross sections. Specifically, outstanding scattering angular distributions, with zero forward- or backward-scattered intensity, (i.e., the so-called Kerker conditions), previously discussed for hypothetical magnetodielectric particles, are now observed for those Si objects in the near infrared. Interesting new consequences for the corresponding optical forces are derived from the interplay, both in and out of resonance, between the electric- and magnetic-induced dipoles.

The Effect of Orientation Angle Compensation on Coherency Matrix and Polarimetric Target Decompositions

Abstract: The polarization orientation angle (OA) of the scattering media affects the polarimetric radar signatures. This paper investigates the effects of orientation compensation on the coherency matrix and the scattering-model-based decompositions by Freeman-Durden and Yamaguchi et al. The Cloude and Pottier decomposition is excluded, because entropy, anisotropy, and alpha angle are roll invariant. We will show that, after orientation compensation, the volume scattering power is consistently decreased, while the double-bounce power has increased. The surface scattering power is relatively unchanged, and the helicity power is roll invariant. All of these characteristics can be explained by the compensation effect on the nine elements of the coherency matrix. In particular, after compensation, the real part of the (HH - VV) · HV* correlation reduces to zero, the intensity of cross-pol |HV| always reduces, and |HH - VV| always increases. This analysis also reveals that the common perception that OA compensation would make a reflection asymmetrical medium completely reflection symmetric is incorrect and that, contrary to the general perception, the four-component decomposition does not use the complete information of the coherency matrix. Only six quantities are included - one more than the Freeman-Durden decomposition, which explicitly assumes reflection symmetry.

Electric and magnetic dipolar response of germanium nanospheres: interference effects, scattering anisotropy, and optical forces

Abstract: Thecoherentcombinationofelectricandmagneticresponsesisthebasisoftheelectro- magnetic behavior of new engineered metamaterials. The basic constituents of their meta-atoms usually have metallic character and consequently high absorption losses. Based on standard "Mie" scattering theory, we found that there is a wide window in the near-infrared (wavelengths 1t o 3μm), where light scattering by lossless submicrometer Ge spherical particles is fully described by their induced electric and magnetic dipoles. The interference between electric and magneticdipolarfieldsisshowntoleadtoanisotropicangulardistributionsofscatteredintensity, including zero backward and almost zero forward scattered intensities at specific wavelengths, which until recently was theoretically established only for hypothetically postulated magnetodi- electric spheres. Although the scattering cross section at zero backward or forward scattering is exactly the same, radiation pressure forces are a factor of 3 higher in the zero forward condition.

Electrically tunable surface-to-bulk coherent coupling in topological insulator thin films

Abstract: We study coherent electronic transport in charge-density-tunable microdevices patterned from thin films of the topological insulator (TI) Bi${}_{2}$Se${}_{3}$. The devices exhibit pronounced electric field effect, including ambipolar modulation of the resistance with an on-and-off ratio of 500%. We show that the weak antilocalization correction to conductance is sensitive to the number of coherently coupled channels, which in a TI includes the top and bottom surfaces and the bulk carriers. These are separated into coherently independent channels by the application of gate voltage and at elevated temperatures. Our results are consistent with a model where channel separation is determined by a competition between the phase coherence time and the surface-to-bulk scattering time.

Single-Crystalline Rutile TiO2 Hollow Spheres: Room-Temperature Synthesis, Tailored Visible-Light-Extinction, and Effective Scattering Layer for Quantum Dot-Sensitized Solar Cells

Abstract: A general synthesis of inorganic single-crystalline hollow spheres has been achieved through a mechanism analogous to the Kirkendall effect, based on a simple one-step laser process performed at room temperature. Taking TiO(2) as an example, we describe the laser process by investigating the influence of experimental parameters, for example, laser wavelength, laser fluence/irradiation time, liquid medium, and concentration of starting materials, on the formation of hollow spheres. It was found that the size-tailored TiO(2) hollow spheres demonstrate tunable light scattering over a wide visible-light range. Inspired by the effect of light scattering, we introduced the TiO(2) hollow sphere's scattering layer in quantum dot-sensitized solar cells and achieved a current notable 10% improvement of solar-to-electric conversion efficiency, indicating that TiO(2) hollow spheres are potential candidates in optical and optoelectronic devices.

Shell-in-shell TiO2 hollow spheres synthesized by one-pot hydrothermal method for dye-sensitized solar cell application

Abstract: A new type of shell-in-shell TiO2 hollow spheres (S@S-TiO2) featuring excellent light scattering properties were synthesized by a facile one-pot hydrothermal method followed by calcination. Various characterizations revealed that the ratio of sucrose to TiF4 in the reagents plays a key role in controlling the hollow architecture and shell thickness of the resultant S@S-TiO2 structure. The excellent light scattering property of S@S-TiO2 makes it a promising candidate for use as the scattering layer in dye-sensitized solar cells. A bilayer structured photoelectrode consisting of the S@S-TiO2 film as a scattering layer on top of the benchmark TiO2 P25 thin film exhibited an overall conversion efficiency of 9.10% under AM-1.5G one sun light intensity, in comparison with the 7.65% efficiency for a pristine P25 photoanode.

Circular photogalvanic effect on topological insulator surfaces: Berry-curvature-dependent response

Abstract: We study theoretically the optical response of the surface states of a topological insulator, especially the generation of helicity-dependent direct current by circularly polarized light Interestingly, the dominant current, due to an interband transition, is controlled by the Berry curvature of the surface bands This extends the connection between photocurrents and Berry curvature beyond the quasiclassical approximation, where it has been shown to hold Explicit expressions are derived for the (111) surface of the topological insulator Bi${}_{2}$Se${}_{3}$, where we find significant helicity-dependent photocurrents when the rotational symmetry of the surface is broken by an in-plane magnetic field or a strain Moreover, the dominant current grows linearly with time until a scattering occurs, which provides a means for determining the scattering time The dc spin generated on the surface is also dominated by a linear-in-time, Berry curvature-dependent contribution