Showing papers on "Scattering published in 2016"
TL;DR: This work investigates the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, and discovers that scattering from longitudinal optical phonons via the Fröhlich interaction is the dominant source of electron–phonon coupling near room temperature.
Abstract: Phonon scattering limits charge-carrier mobilities and governs emission line broadening in hybrid metal halide perovskites. Establishing how charge carriers interact with phonons in these materials is therefore essential for the development of high-efficiency perovskite photovoltaics and low-cost lasers. Here we investigate the temperature dependence of emission line broadening in the four commonly studied formamidinium and methylammonium perovskites, HC(NH2)2PbI3, HC(NH2)2PbBr3, CH3NH3PbI3 and CH3NH3PbBr3, and discover that scattering from longitudinal optical phonons via the Frohlich interaction is the dominant source of electron–phonon coupling near room temperature, with scattering off acoustic phonons negligible. We determine energies for the interacting longitudinal optical phonon modes to be 11.5 and 15.3 meV, and Frohlich coupling constants of ∼40 and 60 meV for the lead iodide and bromide perovskites, respectively. Our findings correlate well with first-principles calculations based on many-body perturbation theory, which underlines the suitability of an electronic band-structure picture for describing charge carriers in hybrid perovskites. Phonon scattering limits charge transport in perovskite solar cells, yet the interactions involved are still poorly understood. Here, Wright et al. show by photoluminescence measurements and first-principles calculations that longitudinal optical phonons dominate the electron-phonon coupling at room temperature.
912 citations
01 Jan 2016
TL;DR: In this paper, it was shown that the nucleus is the seat of the essential part of the mass of the atom and has linear dimensions exceedingly small compared with the linear dimensions of the whole atom, and the number of electrons in an atom is approximately equal to half the atomic weight.
Abstract: In order to explain the results of experiments on scattering of α rays by matter Prof. Rutherford1 has given a theory of the structure of atoms. According to this theory, the atoms consist of a positively charged nucleus surrounded by a system of electrons kept together by attractive forces from the nucleus; the total negative charge of the electrons is equal to the positive charge of the nucleus. Further, the nucleus is assumed to be the seat of the essential part of the mass of the atom, and to have linear dimensions exceedingly small compared with the linear dimensions of the whole atom. The number of electrons in an atom is deduced to be approximately equal to half the atomic weight. Great interest is to be attributed to this atom-model; for, as Rutherford has shown, the assumption of the existence of nuclei, as those in question, seems to be necessary in order to account for the results of the experiments on large angle scattering of the α rays.2
764 citations
TL;DR: This work provides a theoretical foundation for X-ray scattering, considering both form factor and structure factor, as well as the use of correlation functions, which may be used to determine a particle's size, size distribution, shape, and organization into hierarchical structures.
Abstract: X-ray scattering is a structural characterization tool that has impacted diverse fields of study. It is unique in its ability to examine materials in real time and under realistic sample environments, enabling researchers to understand morphology at nanometer and angstrom length scales using complementary small and wide angle X-ray scattering (SAXS, WAXS), respectively. Herein, we focus on the use of SAXS to examine nanoscale particulate systems. We provide a theoretical foundation for X-ray scattering, considering both form factor and structure factor, as well as the use of correlation functions, which may be used to determine a particle’s size, size distribution, shape, and organization into hierarchical structures. The theory is expanded upon with contemporary use cases. Both transmission and reflection (grazing incidence) geometries are addressed, as well as the combination of SAXS with other X-ray and non-X-ray characterization tools. We conclude with an examination of several key areas of research w...
611 citations
TL;DR: Diverse electromagnetic responses of a programmable metasurface with a relatively large scale have been investigated, where multiple functionalities are obtained on the same surface and various EM phenomena including anomalous reflection, diffusion, beam steering and beam forming are successfully demonstrated.
Abstract: Diverse electromagnetic (EM) responses of a programmable metasurface with a relatively large scale have been investigated, where multiple functionalities are obtained on the same surface. The unit cell in the metasurface is integrated with one PIN diode, and thus a binary coded phase is realized for a single polarization. Exploiting this anisotropic characteristic, reconfigurable polarization conversion is presented first. Then the dynamic scattering performance for two kinds of sources, i.e. a plane wave and a point source, is carefully elaborated. To tailor the scattering properties, genetic algorithm, normally based on binary coding, is coupled with the scattering pattern analysis to optimize the coding matrix. Besides, inverse fast Fourier transform (IFFT) technique is also introduced to expedite the optimization process of a large metasurface. Since the coding control of each unit cell allows a local and direct modulation of EM wave, various EM phenomena including anomalous reflection, diffusion, beam steering and beam forming are successfully demonstrated by both simulations and experiments. It is worthwhile to point out that a real-time switch among these functionalities is also achieved by using a field-programmable gate array (FPGA). All the results suggest that the proposed programmable metasurface has great potentials for future applications.
466 citations
TL;DR: In this article, the authors review the recent resonant X-ray scattering breakthroughs in the copper oxide high-temperature superconductors, in particular regarding the phenomenon of charge order, a broken-symmetry state occurring when valence electrons self-organize into periodic structures.
Abstract: X-ray techniques have been used for more than a century to study the atomic and electronic structure in practically any type of material. The advent of correlated electron systems, in particular complex oxides, brought about new scientific challenges and opportunities for the advancement of conventional X-ray methods. In this context, the need for new approaches capable of selectively sensing new forms of orders involving all degrees of freedom—charge, orbital, spin, and lattice—paved the way for the emergence and success of resonant X-ray scattering, which has become an increasingly popular and powerful tool for the study of electronic ordering phenomena in solids. We review the recent resonant X-ray scattering breakthroughs in the copper oxide high-temperature superconductors, in particular regarding the phenomenon of charge order, a broken-symmetry state occurring when valence electrons self-organize into periodic structures. After a brief historical perspective on charge order, we outline the mileston...
350 citations
TL;DR: In this paper, the authors used density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS.
Abstract: Dark matter in the sub-GeV mass range is a theoretically motivated but largely unexplored paradigm. Such light masses are out of reach for conventional nuclear recoil direct detection experiments, but may be detected through the small ionization signals caused by dark matter-electron scattering. Semiconductors are well-studied and are particularly promising target materials because their $$ \mathcal{O} $$
(1 eV) band gaps allow for ionization signals from dark matter particles as light as a few hundred keV. Current direct detection technologies are being adapted for dark matter-electron scattering. In this paper, we provide the theoretical calculations for dark matter-electron scattering rate in semiconductors, overcoming several complications that stem from the many-body nature of the problem. We use density functional theory to numerically calculate the rates for dark matter-electron scattering in silicon and germanium, and estimate the sensitivity for upcoming experiments such as DAMIC and SuperCDMS. We find that the reach for these upcoming experiments has the potential to be orders of magnitude beyond current direct detection constraints and that sub-GeV dark matter has a sizable modulation signal. We also give the first direct detection limits on sub-GeV dark matter from its scattering off electrons in a semiconductor target (silicon) based on published results from DAMIC. We make available publicly our code, QEdark
, with which we calculate our results. Our results can be used by experimental collaborations to calculate their own sensitivities based on their specific setup. The searches we propose will probe vast new regions of unexplored dark matter model and parameter space.
313 citations
01 Jan 2016
TL;DR: The only reasonable correction method for an absorption meter without attenuation measurements or a spectrophotometer is the method in which the measured absorption at a wavelength in the near infrared is subtracted as mentioned in this paper.
Abstract: In this paper we examine correction methods for the scattering error of reflecting tube absorption meters and spectrophotometers. We model the scattering error of reflecting tube absorption meters for different tube parameters and different inherent optical properties. We show that the only reasonable correction method for an absorption meter without attenuation measurements or a spectrophotometer is the method in which the measured absorption at a wavelength in the near infrared is subtracted. A better correction is obtained if attenuation is measured simultaneously and the absorption at the reference wavelength is multiplied by the ratio of the measured scattering at the measurement wavelength divided by the measured scattering coefficient at the reference wavelength. This is the proportional method. We showed that the important geometrical parameters of the reflecting tube can be obtained by a comparison of measurements and models of polystyrene beads. Finally we examine the improvements that could be obtained if a direct scattering measurement were made simultaneously with the absorption and attenuation measurements.
282 citations
TL;DR: A new class of superconducting detectors that are sensitive to O(meV) electron recoils from dark matter-electron scattering are proposed and demonstrated that classes of dark matter consistent with terrestrial and cosmological or astrophysical constraints could be detected by such detectors with a moderate size exposure.
Abstract: We propose and study a new class of superconducting detectors that are sensitive to O(meV) electron recoils from dark matter-electron scattering. Such devices could detect dark matter as light as the warm dark-matter limit, m(X)≳1 keV. We compute the rate of dark-matter scattering off of free electrons in a (superconducting) metal, including the relevant Pauli blocking factors. We demonstrate that classes of dark matter consistent with terrestrial and cosmological or astrophysical constraints could be detected by such detectors with a moderate size exposure.
241 citations
TL;DR: In this paper, the second harmonic and sum-frequency generation (SHG/SFG) was used to characterize the electrical double layer of aqueous systems and showed that interference effects from oriented water molecules on a length scale over which the potential decays, can strongly modify the probing depth as well as the expected intensity at ionic strengths <10−3 M.
Abstract: The interfacial region of aqueous systems also known as the electrical double layer can be characterized on the molecular level with second harmonic and sum-frequency generation (SHG/SFG). SHG and SFG are surface specific methods for isotropic liquids. Here, we model the SHG/SFG intensity in reflection, transmission, and scattering geometry taking into account the spatial variation of all fields. We show that, in the presence of a surface electrostatic field, interference effects, which originate from oriented water molecules on a length scale over which the potential decays, can strongly modify the probing depth as well as the expected intensity at ionic strengths <10–3 M. For reflection experiments this interference phenomenon leads to a significant reduction of the SHG/SFG intensity. Transmission mode experiments from aqueous interfaces are hardly influenced. For SHG/SFG scattering experiments the same interference leads to an increase in intensity and to modified scattering patterns. The predicted sca...
240 citations
TL;DR: The substantial reduction of light scattering multiplicity at tissue optical clearing that leads to a lesser influence of scattering on the measured intrinsic polarization properties of the tissue and allows for more precise quantification of these properties is demonstrated.
Abstract: This tutorial-review introduces the fundamentals of polarized light interaction with biological tissues and presents some of the recent key polarization optical methods that have made possible the quantitative studies essential for biomedical diagnostics. Tissue structures and the corresponding models showing linear and circular birefringence, dichroism, and chirality are analyzed. As the basis for a quantitative description of the interaction of polarized light with tissues, the theory of polarization transfer in a random medium is used. This theory employs the modified transfer equation for Stokes parameters to predict the polarization properties of single- and multiple-scattered optical fields. The near-order of scatterers in tissues is accounted for to provide an adequate description of tissue polarization properties. Biomedical diagnostic techniques based on polarized light detection, including polarization imaging and spectroscopy, amplitude and intensity light scattering matrix measurements, and polarization-sensitive optical coherence tomography are described. Examples of biomedical applications of these techniques for early diagnostics of cataracts, detection of precancer, and prediction of skin disease are presented. The substantial reduction of light scattering multiplicity at tissue optical clearing that leads to a lesser influence of scattering on the measured intrinsic polarization properties of the tissue and allows for more precise quantification of these properties is demonstrated.
231 citations
TL;DR: In this paper, an extremely low lattice thermal conductivity of 0.5 W m−1 K−1 was achieved in SnTe-Cu2Te solid solutions, which is actually approaching the amorphous limit of SnTe.
Abstract: Due to point defect phonon scattering, formation of solid solutions has long been considered as an effective approach for enhancing thermoelectric performance through reducing the lattice thermal conductivity. The scattering of phonons by point defects mainly comes from the mass and strain fluctuations between the guest and the host atoms. Both the fluctuations can be maximized by point defects of interstitial atoms and/or vacancies in a crystal. Here, a demonstration of phonon scattering by interstitial Cu atoms is shown, leading to an extremely low lattice thermal conductivity of 0.5 W m−1 K−1 in SnTe-Cu2Te solid solutions. This is the lowest lattice thermal conductivity reported in SnTe-based materials so far, which is actually approaching the amorphous limit of SnTe. As a result, a peak thermoelectric figure of merit, zT, higher than 1 is achieved in Sn0.94Cu0.12Te at 850 K, without relying on other approaches for electrical performance enhancements. The strategy used here is believed to be equally applicable in thermoelectrics with interstitial point defects.
TL;DR: The proposed digital metasurfaces provide simple designs and reveal new opportunities for controlling electromagnetic wave scattering with or without polarization dependence.
Abstract: Ultrathin metasurface compromising various sub-wavelength meta-particles offers promising advantages in controlling electromagnetic wave by spatially manipulating the wavefront characteristics across the interface. The recently proposed digital coding metasurface could even simplify the design and optimization procedures due to the digitalization of the meta-particle geometry. However, current attempts to implement the digital metasurface still utilize several structural meta-particles to obtain certain electromagnetic responses, and requiring time-consuming optimization especially in multi-bits coding designs. In this regard, we present herein utilizing geometric phase based single structured meta-particle with various orientations to achieve either 1-bit or multi-bits digital metasurface. Particular electromagnetic wave scattering patterns dependent on the incident polarizations can be tailored by the encoded metasurfaces with regular sequences. On the contrast, polarization insensitive diffusion-like scattering can also been successfully achieved by digital metasurface encoded with randomly distributed coding sequences leading to substantial suppression of backward scattering in a broadband microwave frequency. The proposed digital metasurfaces provide simple designs and reveal new opportunities for controlling electromagnetic wave scattering with or without polarization dependence.
TL;DR: The findings demonstrate that synchrotron X-ray scattering is a viable method for studying self-assembly in its native environment, with ample time resolution to extract kinetic rates and observe intermediate configurations and to better understand the forces governing self-organization of soft materials.
Abstract: The self-assembly of lead sulfide nanocrystals into a body-centred cubic lattice can be tracked in real time by using in situ grazing-incidence X-ray scattering.
TL;DR: In this paper, the role of third-order multipoles in the resonant optical response of high-refractive-index dielectric nanodisks, with and without a through hole at the center, is investigated.
Abstract: The application of Cartesian multipoles in irreducible representations provides the possibility to get explicit contributions of the toroidal multipole terms in the extinction and scattering power without the introduction of special form factors. In the framework of the Cartesian multipoles, we obtained multipole decomposition (up to the third order) of the induced polarization (current) inside an arbitrarily shaped scatterer (nanoparticle). The third-order decomposition includes the toroidal dipole, magnetic quadrupole, electric octupole terms, and also nonradiating terms. The corresponding multipole decomposition of the scattering cross section, taking into account the electric octupole term, is derived and compared with the multipole decomposition of the extinction cross section obtained using the optical theorem. We show that the role of multipoles in the optical theorem (light extinction) and scattering by arbitrarily shaped nanoparticles can be different. This can result in seemingly paradoxical conclusions with respect to the appearance of multipole contributions in the scattering and extinction cross sections. This fact is especially important for absorptionless nanoparticles, for which the scattering cross section can be calculated using the optical theorem, because in this case extinction is solely determined by scattering. Demonstrative results concerning the role of third-order multipoles in the resonant optical response of high-refractive-index dielectric nanodisks, with and without a through hole at the center, are presented. It is shown that the optical theorem results in a negligible role of the third-order multipoles in the extinction cross sections, whereas these multipoles provide the main contribution in the scattering cross sections.
TL;DR: It is shown how dipolar interactions can suppress off-axis scattering in a two-dimensional atomic array, leading to a subradiant collective mode where the optical cross section is enhanced by almost an order of magnitude, implying high-fidelity extinction, from a monolayer.
Abstract: Enhancing the optical cross section is an enticing goal in light-matter interactions, due to its fundamental role in quantum and nonlinear optics. Here, we show how dipolar interactions can suppress off-axis scattering in a two-dimensional atomic array, leading to a subradiant collective mode where the optical cross section is enhanced by almost an order of magnitude. As a consequence, it is possible to attain an optical depth which implies high-fidelity extinction, from a monolayer. Using realistic experimental parameters, we also model how lattice vacancies and the atomic trapping depth affect the transmission, concluding that such high extinction should be possible, using current experimental techniques.
TL;DR: The results show that scatterings via deformation potential by acoustic and homopolar optical phonons are the main scattering mechanisms for excitons in ultrathin single exfoliated flakes, with the absence of polar optical phonon and defect scattering to efficient screening of Coulomb potential, similar to what has been observed in 3D perovskites.
Abstract: Two-dimensional (2D) atomically thin perovskites with strongly bound excitons are highly promising for optoelectronic applications. However, the nature of nonradiative processes that limit the photoluminescence (PL) efficiency remains elusive. Here, we present time-resolved and temperature-dependent PL studies to systematically address the intrinsic exciton relaxation pathways in layered (C4H9NH3)2(CH3NH3)n−1PbnI3n+1 (n = 1, 2, 3) structures. Our results show that scatterings via deformation potential by acoustic and homopolar optical phonons are the main scattering mechanisms for excitons in ultrathin single exfoliated flakes, exhibiting a Tγ (γ = 1.3 to 1.9) temperature dependence for scattering rates. We attribute the absence of polar optical phonon and defect scattering to efficient screening of Coulomb potential, similar to what has been observed in 3D perovskites. These results establish an understanding of the origins of nonradiative pathways and provide guidelines for optimizing PL efficiencies of...
TL;DR: In this article, the structure of Roy-Steiner equations for pion-nucleon scattering, the solution for the partial waves of the t -channel process π π → N N, as well as the high-accuracy extraction of the pionnucleons S -wave scattering lengths from data on pionic hydrogen and deuterium are reviewed.
TL;DR: The measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk.
Abstract: Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to propagate through the bulk when their momentum matches that of the surface projections of the bulk’s Weyl nodes. We used spectroscopic mapping with a scanning tunneling microscope to visualize quasiparticle scattering and interference at the surface of the Weyl semimetal TaAs. Our measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk. Our findings provide evidence that Weyl nodes act as sinks for electron transport on the surface of these materials.
01 Jan 2016
TL;DR: In this paper, it was shown that the characteristic effects of an isolated force acting at the center of the strip are not appreciable at a distance from the force equal to the width of a strip, when the force is longitudinal, or equal to 11 times the length of the width when the forces are transverse.
Abstract: To summarise the results obtained, we may say that the characteristic effects of an isolated force acting at the centre of the strip are not appreciable at a distance from the force equal to the width of the strip, when the force is longitudinal, or equal to 11 times the width of the strip when the force is transverse. The conditions at a "freely-supported" end may be closely imitated at any distance exceeding 11 times the width.
TL;DR: In this paper, a formalism is developed to explicitly determine quantum mechanical scattering probability matrices for four-phonon scattering in the full Brillouin zone, and by mitigating the computational challenge, the authors have directly calculated fourphonson scattering rates.
Abstract: Recently, first principle-based predictions of lattice thermal conductivity $\ensuremath{\kappa}$ from perturbation theory have achieved significant success. However, it only includes three-phonon scattering due to the assumption that four-phonon and higher-order processes are generally unimportant. Also, directly evaluating the scattering rates of four-phonon and higher-order processes has been a long-standing challenge. In this work, however, we have developed a formalism to explicitly determine quantum mechanical scattering probability matrices for four-phonon scattering in the full Brillouin zone, and by mitigating the computational challenge we have directly calculated four-phonon scattering rates. We find that four-phonon scattering rates are comparable to three-phonon scattering rates at medium and high temperatures, and they increase quadratically with temperature. As a consequence, $\ensuremath{\kappa}$ of Lennard-Jones argon is reduced by more than 60% at 80 K when four-phonon scattering is included. Also, in less anharmonic materials---diamond, silicon, and germanium---$\ensuremath{\kappa}$ is still reduced considerably at high temperature by four-phonon scattering by using the classical Tersoff potentials. Also, the thermal conductivity of optical phonons is dominated by the fourth- and higher-orders phonon scattering even at low temperature.
TL;DR: It is shown that, at large detuning, the decay rate of the off-axis fluorescence of a large and dilute cloud of cold rubidium atoms after the sudden switch off of a low-intensity laser driving the atomic transition increases with the on-resonance optical depth.
Abstract: Superradiance has been extensively studied in the 1970s and 1980s in the regime of superfluorescence, where a large number of atoms are initially excited. Cooperative scattering in the linear-optics regime, or "single-photon superradiance," has been investigated much more recently, and superradiant decay has also been predicted, even for a spherical sample of large extent and low density, where the distance between atoms is much larger than the wavelength. Here, we demonstrate this effect experimentally by directly measuring the decay rate of the off-axis fluorescence of a large and dilute cloud of cold rubidium atoms after the sudden switch off of a low-intensity laser driving the atomic transition. We show that, at large detuning, the decay rate increases with the on-resonance optical depth. In contrast to forward scattering, the superradiant decay of off-axis fluorescence is suppressed near resonance due to attenuation and multiple-scattering effects.
TL;DR: The power spectrum and two-point correlation function for the randomly fluctuating free surface on the downstream side of a stationary flow with a maximum Froude number F_{max}≈0.85 and the noise show a clear correlation between pairs of modes of opposite energies.
Abstract: We measured the power spectrum and two-point correlation function for the randomly fluctuating free surface on the downstream side of a stationary flow with a maximum Froude number ${F}_{\mathrm{max}}\ensuremath{\approx}0.85$ reached above a localized obstacle. On such a flow the scattering of incident long wavelength modes is analogous to that responsible for black hole radiation (the Hawking effect). Our measurements of the noise show a clear correlation between pairs of modes of opposite energies. We also measure the scattering coefficients by applying the same analysis of correlations to waves produced by a wave maker.
TL;DR: Resonant x-ray scattering shows that the bulk structure of the twist-bend liquid crystal phase, recently discovered in bent molecular dimers, has spatial periodicity without electron density modulation, indicating a lattice-free heliconical nematic precession of orientation that has helical glide symmetry.
Abstract: Resonant x-ray scattering shows that the bulk structure of the twist-bend liquid crystal phase, recently discovered in bent molecular dimers, has spatial periodicity without electron density modulation, indicating a lattice-free heliconical nematic precession of orientation that has helical glide symmetry. In situ study of the bulk helix texture of the dimer CB7CB shows an elastically confined temperature-dependent minimum helix pitch, but a remarkable elastic softness of pitch in response to dilative stresses. Scattering from the helix is not detectable in the higher temperature nematic phase.
TL;DR: Differences in these distributions must be present, as a result of the species-dependent scattering cross sections lower in the star, to lead to a new set of nonlinear equations, unstable even at the initial surface with respect to perturbations that break all-over spherical symmetry.
Abstract: Most treatments of neutrino flavor evolution, above a surface of the last scattering, take identical angular distributions on this surface for the different initial (unmixed) flavors, and for particles and antiparticles. Differences in these distributions must be present, as a result of the species-dependent scattering cross sections lower in the star. These lead to a new set of nonlinear equations, unstable even at the initial surface with respect to perturbations that break all-over spherical symmetry. There could be important consequences for explosion dynamics as well as for the neutrino pulse in the outer regions.
TL;DR: At high temperature the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers, however, closer to room temperature the inELastic carrier-optical-phonon scattering becomes more significant and limits theTEP below thehydrodynamic prediction.
Abstract: We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons.
TL;DR: This work presents a machine-learning-based method for single-shot imaging through scattering media that enables model-free sensing, where it is not necessary to know the sensing processes/models.
Abstract: We present a machine-learning-based method for single-shot imaging through scattering media. The inverse scattering process was calculated based on a nonlinear regression algorithm by learning a number of training object-speckle pairs. In the experimental demonstration, multilayer phase objects between scattering plates were reconstructed from intensity measurements. Our approach enables model-free sensing, where it is not necessary to know the sensing processes/models.
TL;DR: This review article focuses on the most recent advances in X-ray and neutron scattering studies of water structure, from ambient temperature to the deeply supercooled and amorphous states, and of water diffusive and collective dynamics, in disparate thermodynamic conditions and environments.
Abstract: This review article focuses on the most recent advances in X-ray and neutron scattering studies of water structure, from ambient temperature to the deeply supercooled and amorphous states, and of water diffusive and collective dynamics, in disparate thermodynamic conditions and environments. In particular, the ability to measure X-ray and neutron diffraction of water with unprecedented high accuracy in an extended range of momentum transfers has allowed the derivation of detailed O-O pair correlation functions. A panorama of the diffusive dynamics of water in a wide range of temperatures (from 400 K down to supercooled water) and pressures (from ambient up to multiple gigapascals) is presented. The recent results obtained by quasi-elastic neutron scattering under high pressure are compared with the existing data from nuclear magnetic resonance, dielectric and infrared measurements, and modeling. A detailed description of the vibrational dynamics of water as measured by inelastic neutron scattering is presented. The dependence of the water vibrational density of states on temperature and pressure, and in the presence of biological molecules, is discussed. Results about the collective dynamics of water and its dispersion curves as measured by coherent inelastic neutron scattering and inelastic X-ray scattering in different thermodynamic conditions are reported.
TL;DR: By combining a matrix discrimination of ballistic waves and iterative time reversal, this work shows an extension of the imaging-depth limit by at least a factor of 2 compared to optical coherence tomography.
Abstract: Multiple scattering of waves in disordered media is a nightmare whether it is for detection or imaging purposes. So far, the best approach to get rid of multiple scattering is optical coherence tomography. This basically combines confocal microscopy and coherence time gating to discriminate ballistic photons from a predominant multiple scattering background. Nevertheless, the imaging-depth range remains limited to 1 mm at best in human soft tissues because of aberrations and multiple scattering. We propose a matrix approach of optical imaging to push back this fundamental limit. By combining a matrix discrimination of ballistic waves and iterative time reversal, we show, both theoretically and experimentally, an extension of the imaging-depth limit by at least a factor of 2 compared to optical coherence tomography. In particular, the reported experiment demonstrates imaging through a strongly scattering layer from which only 1 reflected photon out of 1000 billion is ballistic. This approach opens a new route toward ultra-deep tissue imaging.
TL;DR: In this paper, the authors investigate collective emission from coherently driven ultracold (88)Sr atoms and perform two sets of experiments using a strong and weak transition that are insensitive and sensitive, respectively, to atomic motion at 1 μK.
Abstract: We investigate collective emission from coherently driven ultracold (88)Sr atoms. We perform two sets of experiments using a strong and weak transition that are insensitive and sensitive, respectively, to atomic motion at 1 μK. We observe highly directional forward emission with a peak intensity that is enhanced, for the strong transition, by >10(3) compared with that in the transverse direction. This is accompanied by substantial broadening of spectral lines. For the weak transition, the forward enhancement is substantially reduced due to motion. Meanwhile, a density-dependent frequency shift of the weak transition (∼10% of the natural linewidth) is observed. In contrast, this shift is suppressed to <1% of the natural linewidth for the strong transition. Along the transverse direction, we observe strong polarization dependences of the fluorescence intensity and line broadening for both transitions. The measurements are reproduced with a theoretical model treating the atoms as coherent, interacting radiating dipoles.