Angular Pattern Research Articles

Comparison of back focal plane imaging of nitrogen vacancy centers in nanodiamond and core-shell CdSe/CdS quantum dots

We report on the characterization of the angular-dependent emission of two different single-photon emitters based on nitrogen-vacancy centers in nanodiamond and on core-shell CdSe/CdS quantum dot nanoparticles. The emitters were characterized in a confocal microscope setup by spectroscopy and Hanbury-Brown and Twiss interferometry. The angular-dependent emission is measured using a back focal plane imaging technique. A theoretical model of the angular emission patterns of the 2D dipoles of the emitters is developed to determine their orientation. Experiment and model agree well with each other.

Plasmonics on a Neural Implant: Engineering Light–Matter Interactions on the Nonplanar Surface of Tapered Optical Fibers (Advanced Optical Materials 2/2022)

In article number 2101649, Filippo Pisano and co-workers demonstrate a first step towards implantable multimodal plasmonic neural interfaces. This was achieved by integrating highly-curved plasmonic nanostructures on a tapered optical fiber in order to engineer the spectral and angular patterns of optical emission and collection, with applications to fluorescence and Raman spectroscopy. [Cover image: artwork by Antonio Balena.]

Modeling of Surface Roughness With an Anisotropic Power-Law Spectrum and Its Applications to Radar Backscattering From Soil Surfaces

We present a generalized power-law roughness spectrum to account for the spatial anisotropy effects on the radar scattering of a rough surface, where both the correlation anisotropy and the scaling anisotropy are accounted for. The spatial anisotropy is essential to correctly interpret the radar scattering from an agriculture field where both plow and sow are practiced. We investigate the dependence of the backscattering coefficient on the correlation anisotropy and the scaling anisotropy through a model simulation. A drastic change in backscattering strength is observed due to the anisotropy. The correlation anisotropy and the scaling anisotropy generate similar backscattering angular behavior, implying that in the context of spatial anisotropy, merely using correlation length in scattering modeling is insufficient. Equivalently, the correlation length retrieved from the backscattering coefficients perhaps is not unique. Fair use of the generalized anisotropic power-law roughness spectrum in conjunction with the scattering model is illustrated by comparing the backscattering coefficients with experimental measurements. However, the anisotropy complicates the roughness description in terms of surface parameters retrieval because we can generate similar backscattering angular patterns by combining different correlation anisotropy and scaling anisotropy. When the soil moisture is of primary interest, a more suitable radar observation geometry to minimize the spatial anisotropy influence is desirable.

Planar laser-induced fluorescence measurement of the angular pattern of the cone-shaped spray

In the present work, a PLIF-based approach for a large cone-shaped spray patternation ispresented and experimental results of its application are discussed. The patternation approach is based on simple time-averaged PLIF imaging. Special attention is paid to the image and data processing in order to simplify a patternation results interpretation. Experimental testing was performed on a water spray, formed by centrifugal nozzle at atmospheric ambient pressure. Circumferential relative concentration profiles in spray crosswise plane are presented in the paper and their validity is analysed.

Cramér-Rao Bounds for Holographic Positioning

Multiple antennas arrays combined with high carrier frequencies play a key role in wireless networks for communications but also for localization and sensing applications. To understand the fundamental limits of electromagnetically large antenna arrays for localization, this paper combines wave propagation theory with estimation theory, and computes the Cramér-Rao Bound (CRB) for the estimation of the source position on the basis of the three Cartesian components of the electric field, observed over a rectangular surface area. The problem is referred to as holographic positioning and it intrinsically depends on the radiation angular pattern of the transmitting source, which is typically ignored in standard signal processing models. We assume that the source is a Hertzian dipole, and address the holographic positioning problem in both cases, that is, with and without a priori knowledge of its orientation. To simplify the analysis and gain further insights, we also consider the case in which the dipole is located on the line perpendicular to the surface center. Numerical and asymptotic results are given to quantify the CRBs, and to quantify the effect of various system parameters on the ultimate estimation accuracy. It turns out that square surfaces with side comparable to the distance are needed to guarantee a centimeter-level accuracy in the mmWave bands. Moreover, we show that the CRBs with and without a priori knowledge of the source dipole orientation are numerically the same. The provided CRBs are also used to benchmark different maximum-likelihood estimators (MLEs) derived on the basis of a discrete representation of different models of the electric field. The analysis shows that, if the standard models are used (neglecting the radiation angular pattern), the MLE accuracy is far from the CRB. On the other hand, it approaches the CRB when the more detailed electromagnetic model is considered.

The Effects of Mandarin Chinese Lexical Tones in Sound-Shape and Sound-Size Correspondences.

Crossmodal correspondences refer to when specific domains of features in different sensory modalities are mapped. We investigated how vowels and lexical tones drive sound-shape (rounded or angular) and sound-size (large or small) mappings among native Mandarin Chinese speakers. We used three vowels (/i/, /u/, and /a/), and each vowel was articulated in four lexical tones. In the sound-shape matching, the tendency to match the rounded shape was decreased in the following order: /u/, /i/, and /a/. Tone 2 was more likely to be matched to the rounded pattern, whereas Tone 4 was more likely to be matched to the angular pattern. In the sound-size matching, /a/ was matched to the larger object more than /u/ and /i/, and Tone 2 and Tone 4 correspond to the large-small contrast. The results demonstrated that both vowels and tones play prominent roles in crossmodal correspondences, and sound-shape and sound-size mappings are heterogeneous phenomena.

Plasmonics on a Neural Implant: Engineering Light–Matter Interactions on the Nonplanar Surface of Tapered Optical Fibers

AbstractOptical methods are driving a revolution in neuroscience. Ignited by optogenetic techniques, a set of strategies has emerged to control and monitor neural activity in deep brain regions using implantable photonic probes. A yet unexplored technological leap is exploiting nanoscale light‐matter interactions for enhanced bio‐sensing, beam‐manipulation and opto‐thermal heat delivery in the brain. To bridge this gap, we got inspired by the brain cells’ scale to propose a nano‐patterned tapered‐fiber neural implant featuring highly‐curved plasmonic structures (30 μm radius of curvature, sub‐50 nm gaps). We describe the nanofabrication process of the probes and characterize their optical properties. We suggest a theoretical framework using the interaction between the guided modes and plasmonic structures to engineer the electric field enhancement at arbitrary depths along the implant, in the visible/near‐infrared range. We show that our probes can control the spectral and angular patterns of optical transmission, enhancing the angular emission and collection range beyond the reach of existing optical neural interfaces. Finally, we evaluate the application as fluorescence and Raman probes, with wave‐vector selectivity, for multimodal neural applications. We believe our work represents a first step towards a new class of versatile nano‐optical neural implants for brain research in health and disease.

Vision-based human joint angular velocity estimation during squat and walking on a treadmill actions.

Elderly health monitoring, rehabilitation training, and sport supervision could benefit from continuous assessment of joint angle, and angular velocity to identify the joint movement patterns. However, most of the measurement systems are designed based on special kinematic sensors to estimate angular velocities. The study aims to measure the lower limb joint angular velocity based on a 2D vision camera system during squat and walking on treadmill action using deep convolution neural network (CNN) architecture. Experiments were conducted on 12 healthy adults, and six digital cameras were used to capture the videos of the participant actions in lateral and frontal view. The normalized cross-correlation (Ccnorm) analysis was performed to obtain a degree of symmetry of the ground truth and estimated angular velocity waveform patterns. Mean Ccnorm for angular velocity estimation by deep CNN model has higher than 0.90 in walking on the treadmill and 0.89 in squat action. Furthermore, joint-wise angular velocities at the hip, knee, and ankle joints were observed and compared. The proposed system gets higher estimation performance under the lateral view and the frontal view of the camera. This study potentially eliminates the requirement of wearable sensors and proves the applicability of using video-based system to measure joint angular velocities during squat and walking on a treadmill actions.

On-chip unidirectional micro-nano-light sources based on multi-mode cesium lead halide perovskite nanowires

Unidirectional micro-nano-light sources have been widely applied in integrated photonics and optoelectronic devices. In this study, on-chip all-inorganic cesium lead halide perovskite nanowires are employed and excited as a bright light source to generate unidirectional light. Here, we directly image the angular emission patterns of perovskite nanowires by using fluorescence Fourier microscopy. The extinction ratio for the unidirectional emission is achieved up to 11 dB, and the detected minimum polar divergence angle reaches 8.6° in experiments. The emission direction also can be tuned flexibly within the range of 48° by changing the upper surrounding medium. Detailed calculations based on multi-mode expansion theory are used to reveal the inner physical mechanisms. Further analysis of the far-field emission patterns corresponds well with the experiment results. Our works investigating the perovskite nanowire light source emission from the perspective of Fourier space have potential applications in photon-detection and integrated photonics chips.

Strain-induced topological phase transition at (111) SrTiO3 -based heterostructures

The quasi-two-dimensional electronic gas at the (111) ${\mathrm{SrTiO}}_{3}$-based heterostructure interfaces is described by a multiband tight-binding model providing electronic bands in agreement at low energies with photoemission experiments. We analyze both the roles of the spin-orbit coupling and of the trigonal crystal-field effects. We point out the presence of a regime with sizable strain where the band structure exhibits a Dirac cone whose features are consistent with ab initio approaches. The combined effect of spin-orbit coupling and trigonal strain gives rise to nontrivial spin and orbital angular momenta patterns in the Brillouin zone and to quantum spin Hall effect by opening a gap at the Dirac cone. The system can switch from a conducting to a topological insulating state via modification of trigonal strain within a parameter range which is estimated to be experimentally achievable.

Passive Islanding Detection Based on Angular Velocity Harmonic Patterns with Perceptron Neural Network

Traditional islanding detection methods present improper action when the power mismatch between generation and load in the islanding system is small. The minimum power mismatch for correct islanding detection defines the limits os a Non-Detection Zone. This paper proposes an efficient method for islanding detection based on angular velocity harmonic patterns. To accomplish this, the measured frequency is decomposed by a Fourier Transform and applied to a Perceptron artificial neural network for pattern classification. The performance of the proposed method is evaluated by tests on a modified IEEE 34 node test system. Several islanding and non-islanding cases were simulated. The proposed method achived a performance of 88.16% in the classification of harmonic patterns with a small training set. Compared with the Under/Over frequency method, the proposed method represents a performance improvement of 17%.

A fault classification method using dynamic centered one-dimensional local angular binary pattern for a PMSM and drive system

A fault classification method using dynamic centered one-dimensional local angular binary pattern for a PMSM and drive system

Strong inelastic scattering of slow electrons by optical near fields of small nanostructures

The interaction of swift, free-space electrons with confined optical near fields has recently sparked much interest. It enables a new type of photon-induced near-field electron microscopy, mapping local optical near fields around nanoparticles with exquisite spatial and spectral resolution and lies at the heart of quantum state manipulation and attosecond pulse shaping of free electrons. The corresponding interaction of optical near fields with slow electrons has achieved much less attention, even though the lower electron velocity may enhance electron-near-field coupling for small nanoparticles. A first-principle theoretical study of such interactions has been reported very recently by N Talebi (2020 Phys. Rev. Lett. 125 080401). Building up on this work, we investigate, both analytically and numerically, the inelastic scattering of slow electrons by near fields of small nanostructures. For weak fields, this results in distinct angular diffraction patterns that represent, to first order, the Fourier transform of the transverse variation of the scalar near-field potential along the direction perpendicular to the electron propagation. For stronger fields, scattering by the near-field component along the electron trajectory results in a break-up of the energy spectrum into multiple photon orders. Their angular diffraction patterns are given by integer powers of the Fourier transform of the transverse potential variation and are shifting in phase with photon order. Our analytical model offers an efficient approach for studying the effects of electron kinetic energy, near field shape and strength on the slow-electron diffraction pattern and thus may facilitate the experimental observation of these phenomena by, e.g. ultrafast low-energy point-projection microscopy or related techniques. This could provide simultaneous access to different vectorial components of the optical near fields of small nanoparticles.

Few-body correlations in two-dimensional Bose and Fermi ultracold mixtures

Few-body correlations emerging in two-dimensional harmonically trapped mixtures, are comprehensively investigated. The presence of the trap leads to the formation of atom-dimer and trap states, in addition to trimers. The Tan’s contacts of these eigenstates are studied for varying interspecies scattering lengths and mass ratio, while corresponding analytical insights are provided within the adiabatic hyperspherical formalism. The two- and three-body correlations of trimer states are substantially enhanced compared to the other eigenstates. The two-body contact of the atom-dimer and trap states features an upper bound regardless of the statistics, treated semi-classically and having an analytical prediction in the limit of large scattering lengths. Such an upper bound is absent in the three-body contact. Interestingly, by tuning the interspecies scattering length the contacts oscillate as the atom-dimer and trap states change character through the existent avoided-crossings in the energy spectra. For thermal gases, a gradual suppression of the involved two- and three-body correlations is evinced manifesting the impact of thermal effects. Moreover, spatial configurations of the distinct eigenstates ranging from localized structures to angular anisotropic patterns are captured. Our results provide valuable insights into the inherent correlation mechanisms of few-body mixtures which can be implemented in recent ultracold atom experiments and will be especially useful for probing the crossover from few- to many-atom systems.

Morphological study of the rainbow scattering of protons by graphene.

We have studied metamorphoses of the angular rainbow pattern generated by classical rainbow scattering of protons by graphene. To analyze the rainbow pattern, a morphological method was developed. It focuses on the shape of the rainbow pattern rather than on the exact position of rainbow lines or the particle count. It comprises elements of the catastrophe theory, which provides a local model of the rainbow pattern and the reduced potential and an index theory of algebraic topology that allows the evolution of the rainbow pattern to be linked with bifurcations of critical points of the reduced potential. The obtained insight is summarized into five principles that allow an experimentalist to sketch a qualitatively correct rainbow pattern in the impact parameter plane and the distribution of the reduced potential critical points, just by observing the evolution of the angular rainbows. The morphological method should be applicable for the analysis of all structurally stable patterns in nature.

Angle Resolved Scattering Measurement of Multiple Spherical Particles by Fourier Transform

In this paper, we report that the far field diffraction pattern of a specimen which is consisting of an array of spherical particles enables the determination of the size and refractive index of each scattering sphere. The far field 2D angular resolved diffraction pattern, of which the diffraction angle reaches tens of degrees, is measured by CCD camera. On one hand, the diffraction pattern distorted obviously at high angles is corrected for curvature. The amplitude and phase images of the specimen are reconstructed by difference map iterative algorithm. The size of each scattering microsphere is calculated according to its pixel numbers and the image resolution. On the other hand, the diffraction pattern without curvature correction is used to reconstruct the amplitude and phase images of the specimen by HIO algorithm. The amplitude and phase images of each sphere are isolated. Then the angular resolved scattering signals of the individual spheres are quantitatively indicated by Fourier transform. Finally, the refractive index of each microsphere is obtained by fitting the experimental results using Mie theory.

Measuring Droplets Expelled During Endoscopy to Investigate COVID-19 Transmission Risk

Measuring Droplets Expelled During Endoscopy to Investigate COVID-19 Transmission Risk

Second harmonic generation by strongly coupled exciton-plasmons: The role of polaritonic states in nonlinear dynamics.

We investigate second harmonic generation (SHG) from hexagonal periodic arrays of triangular nano-holes of aluminum using a self-consistent methodology based on the hydrodynamics-Maxwell-Bloch approach. It is shown that angular polarization patterns of the far-field second harmonic response abide to threefold symmetry constraints on tensors. When a molecular layer is added to the system and its parameters are adjusted to achieve the strong coupling regime between a localized plasmon mode and molecular excitons, Rabi splitting is observed from the occurrence of both single- and two-photon transition peaks within the SHG power spectrum. It is argued that the splitting observed for both transitions results from direct two-photon transitions between lower and upper polaritonic states of the strongly coupled system. This interpretation can be accounted by a tailored three-level quantum model, with results in agreement with the unbiased numerical approach. Our results suggest that the hybrid states formed in strongly coupled systems directly contribute to the nonlinear dynamics. This opens new directions in designing THz sources and nonlinear frequency converters.

A low density wave's spiral pattern speed, from the tracer separations (age gradient) across a spiral arm in the Milky Way

ABSTRACT We observe the density wave's angular pattern speed Ωp to be near 12–17 km s−1 kpc−1, by the separation between a typical optical H ii region (from the spiral arm's dust lane) and using a H ii-evolution time model TH ii to yield its relative speed, and independently by the separation between a typical radio maser (from the spiral arm's dust lane) with a maser model. The assumption of a fixed circular rotational speed of the gas and stars with galactic radius is employed (neglecting spiral perturbation at mid-radii, nuclear bar influence at small radii, and tidal effects at large radii).

Multiple forgery detection and localization technique for digital video using PCT and NBAP

With the use of easily available video editing gadgets and applications, the authenticity of digital video has now become a significant concern since the last decade. Digital video forgeries based on inter and intra-frames are often used these days for generating false/unlawful means of evidence in many civil/criminal trials. In this paper, a passive technique using the Polar Cosine Transform (PCT) and Neighborhood Binary Angular Pattern (NBAP) along with the GoogleNet model is proposed to detect and localize multiple forgeries in the video. The pre-processing algorithm is used to extract the frames from the input videos and transform 3-D RGB color space to 2-D grayscale space. The features are then extracted using the PCT and NBAP methodologies. The extracted features are then fed to the pre-trained GoogleNet model to identify the forgeries in the video. The proposed technique can detect and localize both intra-frame forgeries and inter-frame forgeries present in the video. Besides, the proposed technique is robust enough to handle the multiple forgeries in the video, even if the video is subjected to noise exposures. With the help of performance measures like accuracy, specificity, precision, recall, and F1-score, we conduct a comprehensive performance assessment to validate the effectiveness of the proposed technique.