Angular Shift Research Articles

Non-reciprocal spatial and quasi-reciprocal angular Goos-Hänchen shifts around double CPA-LPs in PT-symmetric Thue-Morse photonic crystals.

We theoretically investigate the Goos-Hänchen (GH) shifts of reflected light beams in Thue-Morse photonic crystals. The systems are constituted by two Thue-Morse dielectrics multilayers and satisfy parity-time (PT) symmetry. Double coherent perfect absorption laser points (CPA-LPs) are achieved in the parameter space composed of the incident angle and the gain-loss factor. Dramatic changes in the phase of reflection coefficient induce giant positive and negative spatial GH shifts at the CPA-LPs, while great angular GH shifts exist around the exceptional points (EPs). The spatial GH shifts present non-reciprocity for the forward and backward incident light waves near the double CPA-LPs, while the angular GH shifts are quasi-reciprocal. Increasing the Thue-Morse sequence number, these characteristics are approved around multiple CPA-LPs as well. Our work could pave the way to explore high-accuracy optical sensors.

Effect of the incident polarization on in-plane and out-of-plane spin splitting near the critical angle.

To reveal the effect of the incident polarization on the spin splitting of the photonic spin Hall effect (that is, the spatial and angular in-plane and out-of-plane spin splitting), we systematically study the phenomena and characteristics of these four spin splitting generated when the beam with arbitrary linear polarization is reflected from the non-absorbing medium interface and the absorbing medium interface. Several features of the relationship between the incident polarization and the four kinds of spin splitting are found. In addition, It is also found that the in-plane angular and spatial shifts are significantly enhanced near the critical angle, even reaching their theoretical upper limit. However, the out-of-plane shifts are not enhanced. The research in this paper will contribute to a deeper understanding of PSHE. These findings can also provide new ideas and methods for precision metrology, photonic manipulation, and photonic device fabrication.

Stabilization of Copper-Based Biochips with Alumina for Biosensing Application

Surface plasmon resonance devices typically rely on the use of gold-coated surfaces, but the use of more abundant metals is desirable for the long-term development of plasmonic biochips. As a substitute for gold, thin copper films have been deposited on glass coverslips by thermal evaporation. As expected, these films immersed in a water solution initially exhibit an intense plasmonic resonance comparable to gold. However, without protection, an angle-resolved optical analysis shows a rapid degradation of the copper, characterized by a continuous angular shift of the plasmonic resonance curve. We show that copper films protected with a thin layer of aluminum oxide of a few nanometers can limit the oxidation rate for a sufficient time to perform some standard measurements. As the process is simple and compatible with the current biochip production technique, such an approach could pave the way for the production of alternative and more sustainable biochips.

Influence of structural solutions of an improved brake cylinder of a freight car of railway transport on its load in operation

The object of research is the processes of occurrence, perception and redistribution of loads in the design of the car brake cylinder in operation.
 To compensate for angular shifts of the brake cylinder rod at its maximum exit from the housing, improvement measures are proposed. This improvement consists in the use of a safety element to limit the angular movements of the rod when leaving the body.
 The load of the brake cylinder rod during its angular displacements is determined. The condition for ensuring the strength of the rod is obtained.
 The optimal parameters of the pipe of the safety element (limiter) of the brake cylinder rod were determined by its allowable moment of resistance. For the possibility of moving the levers interacting with the stem, special windows are provided in the limiter. It is proposed to fix the limiter to the cover by welding.
 To determine the strength of the brake cylinder, a calculation was made using the finite element method. The results of a robust calculation showed that the maximum equivalent stresses occur in the brake cylinder cover and amount to 118.5 MPa. Therefore, the strength of the brake cylinder is ensured.
 A feature of the obtained results is that the proposed improvement can be applied not only at the stage of designing a brake cylinder, but also at the stage of modernization.
 The sphere of practical use of the obtained results is railway transport. The conditions for the practical use of the results are the absence of deformations of the brake cylinder rod.
 The research carried out will help to improve the efficiency of rolling stock brakes, ensure traffic safety, increase rolling stock speeds, deliver goods, etc. Also, the conducted research will contribute to the creation of developments to improve the reliability of the rolling stock brakes

Positive and negative Goos–Hänchen shifts in anisotropic two-dimensional atomic crystals

In this paper, the positive and negative Goos–Hänchen (GH) shifts in anisotropic two-dimensional atomic crystals are systematically investigated. As an example, the GH shifts including the spatial GH shift and the angular GH shift in the black phosphorus-substrate are studied. It is found that the spatial GH shift and the angular GH shift are sensitive to the incident angle, photon energy, optical axis angle and doping concentration. Further studies have shown that the signs variations of the spatial GH shift stem from a phase mutation of the reflection coefficients, and the angular GH shift is proportional to the angular derivative of the modulus of the reflection coefficients. Based on the above results, a systematic method of positive and negative regulations of GH shifts is explored, and it is found that the positive and negative of spatial GH shift can be flexibly controlled by altering the photon energy or rotating the optical axis angle, and the signs of angular GH shift can be easily regulated by changing the incident angle. Finally, combined with weak measurement techniques, an application scheme for accurately sensing the optical axis angle of black phosphorus based on the amplified GH shifts is proposed. These results can be extensively extended to other anisotropic two-dimensional atomic crystals.

Coherent control of spatial and angular Goos-Hänchen shifts with spontaneously generated coherence and incoherent pumping.

We propose an efficient scheme to manipulate the Goos-Hänchen (GH) shift of a reflected beam from a metal-clad waveguide, where a coherent atomic medium with a Λ-type configuration is employed as the substrate. Using experimentally achievable parameters, we identify the conditions under which spontaneously generated coherence (SGC) allows us to enhance the spatial and angular GH shifts of the reflected beam. With the help of SGC, the relative phases of the probe and control fields can alter the absorption gain and refractive index of the atomic medium, thereby manipulating the magnitudes, signs, and positions of the spatial and angular shifts. Furthermore, the spatial and angular GH shifts can be coherently controlled via adjusting the incoherent pumping rate and the intensity of the control field. Our proposal provides an avenue for the manipulation of spatial and angular GH shifts and potential applications in optical switching and optical steering.

Micro-Motion Parameter Extraction of Multi-Scattering-Point Target Based on Vortex Electromagnetic Wave Radar

In addition to traditional linear Doppler shift, the angular Doppler shift in vortex electromagnetic wave (VEMW) radar systems carrying orbital angular momentum (OAM) can provide more accurate target identification micro-motion parameters, especially the detailed features perpendicular to the radar line-of-sight (LOS) direction. In this paper, a micro-motion feature extraction method for a spinning target with multiple scattering points based on VEMW radar is proposed. First, a multi-scattering-point spinning target detection model using vortex radar is established, and the mathematical mechanism of echo signal flash shift in time-frequency (TF) domain is deduced. Then, linear Doppler shift is eliminated by interference processing with opposite dual-mode VEMW. Subsequently, the shift in TF flicker is focused on the reference zero frequency by the iterative phase compensation method, and the number of scattering points is estimated according to the focusing effect. After this, through the constructed compensation phase, the angular Doppler shift is separated, then the angular velocity, rotation radiusand initial phase of the target are estimated. Theoretical and simulation results verify the effectiveness of the proposed method, and more accurate rotation parameters can be obtained in the case of multiple scattering points using the VEMW radar system.

A phenomenological model of vibration signals of epicyclic gearboxes under meshing impact excitations

A thorough understanding of the formation mechanism of modulation sidebands in the vibration spectra is helpful to the condition monitoring and fault diagnosis of epicyclic gearboxes. However, these sidebands are commonly very abundant and complicated, which brings a considerable difficulty for spectral analysis. Previous phenomenological models, constructed by a series of cosine functions, provide a concise and effective method to represent the spectral structures of vibration signals, while the meshing impacts are often excluded. Aiming at this issue, a phenomenological model of vibration signals of epicyclic gearboxes under meshing impact excitations is proposed in this paper. In the present work, the impact force when gear teeth are engaged into meshing is calculated. Then the effects of meshing impacts on the vibration signals are investigated, and vibration signals including meshing impacts during the external and internal meshing process are simulated. After that, a phenomenological model is established with meshing impacts considered, and the spectral structures of the phenomenological model of epicyclic gearboxes in different health conditions are deduced using Fourier series analysis. In addition, since both the angular shift and the meshing impact can influence the vibration signals of epicyclic gearboxes largely, this paper makes a comparison between these two issues, and the comparison results show that the angular shift may affect the spectrum more seriously. Finally, the established phenomenological model is validated with the experimental vibration data from a test rig, and it is concluded that the proposed model is helpful to the condition monitoring and fault diagnosis of epicyclic gearboxes through the verification.

Non-specular reflection of a narrow spatially phase-modulated Gaussian beam.

The lateral and angular Goos-Hänchen shifts undergone upon reflection on a dielectric plate by a spatially phase-modulated Gaussian beam are derived. It is shown that the amplitude and direction of both lateral and angular shifts are very sensitive to the degree of spatial phase modulation of the incident beam, so that such modulation thus provides a means to control those shifts. It is also shown that the modulation incurs some beam reshaping upon reflection. Analytical calculations of the lateral shift are found to be in good agreement with numerical simulations of beam propagation before and after reflection. In these simulations, the required spatial transverse phase modulation is achieved by focusing a microwave Gaussian beam onto the dielectric plate with a non-spherical lens or a flat-surfaced thin lamella exhibiting a suitable gradient of its refractive index. The optimal parameters governing the spatial phase modulation are discussed to achieve: (i) enhancement of the lateral shift of a spatially phase-modulated beam in comparison to that of a non-modulated beam and (ii) simultaneous large values of reflectivity and of the lateral shift, while keeping the reshaping of the reflected beam to a minimum.

Dual-Energy Cone-Beam CT with Three-Material Decomposition for Bone Marrow Edema Imaging.

We investigate the feasibility of bone marrow edema (BME) detection using a kV-switching Dual-Energy (DE) Cone-Beam CT (CBCT) protocol. This task is challenging due to unmatched x-ray paths in the low-energy (LE) and high-energy (HE) spectral channels, CBCT non-idealities such as x-ray scatter, and narrow spectral separation between fat (bone marrow) and water (BME). We propose a comprehensive DE decomposition framework consisting of projection interpolation onto matching LE and HE view angles, fast Monte Carlo scatter correction with low number of tracked photons and Gaussian denoising, and two-stage three-material decompositions involving two-material (fat-Aluminium) Projection-Domain Decomposition (PDD) followed by image-domain three-material (fat-water-bone) base-change. Performance in BME detection was evaluated in simulations and experiments emulating a kV-switching CBCT wrist imaging protocol on a robotic x-ray system with 60 kV LE beam, 120 kV HE beam, and 0.5° angular shift between the LE and HE views. Cubic B-spline interpolation was found to be adequate to resample HE and LE projections of a wrist onto common view angles required by PDD. The DE decomposition maintained acceptable BME detection specificity (<0.2 mL erroneously detected BME volume compared to 0.85 mL true BME volume) over +/-10% range of scatter magnitude errors, as long as the scatter shape was estimated without major distortions. Physical test bench experiments demonstrated successful discrimination of ~20% change in fat concentrations in trabecular bone-mimicking solutions of varying water and fat content.

Evaluation of intrafraction couch shifts for proton treatment delivery in head-and-neck cancer patients: Toward optimal imaging frequency.

Treatment planning for head-and-neck (H&N) cancer, in particular oropharynx, nasopharynx, and paranasal sinus cases, at our center requires noncoplanar proton beams due to the complexity of the anatomy and target location. Targeting accuracy for all beams is carefully evaluated by using image guidance before delivering proton beam therapy (PBT). In this study, we analyzed couch shifts to evaluate whether imaging is required before delivering each field with different couch angles. After the Institutional Review Board approval, a retrospective analysis was performed on data from 28 H&N patients treated with PBT. Each plan was made with two-to-three noncoplanar and two-to-three coplanar fields. Cone-beam computed tomography and orthogonal kilovoltage (kV) images were acquired for setup and before delivering each field, respectively. The Cartesian (longitudinal, vertical, and lateral) and angular (pitch and roll) shifts for each field were recorded from the treatment summary on the first two fractions and every subsequent fifth fraction. A net magnitude of the three-dimensional (3D) shift in Cartesian coordinates was calculated, and a 3D vector was created from the 6 degrees of freedom coordinates for transforming couch shifts in the system coordinate to the beam's-eye view. A total of 3219 Cartesian and 2146 angular shift values were recorded for 28 patients. Of the Cartesian shifts, 2069 were zero (64.3%), and 1150 (35.7%) were nonzero (range, -7 to 11mm). Of the angular shifts, 1034 (48.2%) were zero, and 1112 (51.8%) were nonzero (range, -3.0° to 3.2°). For 17 patients, the couch shifts increased toward the end of the treatment course. We also found that patients with higher body mass index (BMI) presented increased net couch shifts (p<0.001). With BMI<27, all overall net shift averages were <2mm, and overall maximum net shifts were <6mm. These results confirm the need for orthogonal kV imaging before delivering each field of H&N PBT at our center, where a couch rotation is involved.

17.3: The study on minimizing angular color shift in high resolution Micro‐OLED with Color Filter

In high-resolution and wide-viewing-angle Microdisplay OLED(Micro-OLED) with Color Filter (CF), the control of the color mixture between adjacent sub-pixels is a method to reduce the color shift. With optic simulation, we analyze the dependency of the color mixture on design parameters of the pixel structure such as mainly pixel size, CF size, and CF location. Additionally, we propose the design methodology to minimize the angular color shift.

On anomalous optical beam shifts at near-normal incidence

We develop the theory of optical beam shifts (both Goos–Hänchen and Imbert–Fedorov) for the case of near-normal incidence, when the incident angle becomes comparable with the angular beam divergence. The developed theory uncovers the unified origin of the anomalous beam shift enhancement via the geometric Berry phase singularity. Particularly, we predict the large Goos–Hänchen shift occurring for small incidence angles. We also propose a simple experimental scheme involving a quarter-wave q-plate that allows us to observe the giant transverse and longitudinal, spatial and angular beam shifts simultaneously. Finally, we analyze the relevant beam parameters, polarization structure, and intensity profiles of the shifted transmitted beam. Our results can find applications in spin–orbit photonics, polarization optics, sensing applications, and quantum weak measurements.

Signatures of Multiband Effects in High-Harmonic Generation in Monolayer MoS_{2}.

High-harmonic generation (HHG) in solids has been touted as a way to probe ultrafast dynamics and crystal symmetries in condensed matter systems. Here, we investigate the polarization properties of high-order harmonics generated in monolayer MoS_{2}, as a function of crystal orientation relative to the mid-infrared laser field polarization. At several different laser wavelengths we experimentally observe a prominent angular shift of the parallel-polarized odd harmonics for energies above approximately 3.5eV, and our calculations indicate that this shift originates in subtle differences in the recombination dipole strengths involving multiple conduction bands. This observation is material specific and is in addition to the angular dependence imposed by the dynamical symmetry properties of the crystal interacting with the laser field, and may pave the way for probing the vectorial character of multiband recombination dipoles.

Loss-cone-shift maps for the Earth’s magnetosphere

Because of finite-gyroradii effects, the atmospheric loss cone for energetic particles in the magnetosphere is shifted away from the magnetic-field direction. Using the Tsyganenko T96 magnetic-field model, maps of the magnitude of the angular shift of the loss cone are created for electrons, protons, and singly-ionized oxygen in the nightside magnetosphere. When the shift exceeds about 5°–10°, stochastic scattering of particles occurs. For protons and oxygen, this loss-cone shift is quite large, even in the dipolar portions of the magnetosphere, and stochastic scattering of protons and oxygen can occur in those regions. Hence, the ring-current ion population probably exhibits a robustly shifted loss cone and stochastic scattering in the dipole magnetosphere. For electrons, large loss-cone shifts and stochastic scattering are restricted to the magnetotail near and beyond the transition region.

PhotoElasticFinger: Robot Tactile Fingertip Based on Photoelastic Effect.

The sense of touch is fundamental for a one-to-one mapping between the environment and a robot that physically interacts with the environment. Herein, we describe a tactile fingertip design that can robustly detect interaction forces given data collected from a camera. This design is based on the photoelastic effect observed in silicone matter. Under the force applied to the silicone rubber, owing to the stress-induced birefringence, the light propagating within the silicone rubber is subjected to the angular phase shift, where the latter is proportional to the increase in the image brightness in the camera frames. We present the calibration and test results of the photoelastic sensor design on a bench using a robot arm and with a certified industrial force torque sensor. We also discuss the applications of this sensor design and its potential relationship with human mechano-transduction receptors. We achieved a force sensing range of up to 8 N with a force resolution of around 0.5 N. The photoelastic tactile fingertip is suitable for robot grasping and might lead to further progress in robust tactile sensing.

High-speed astigmatic dual-beam interferometric particle imaging for direct depth displacement and velocity measurement of metal droplet

High-speed astigmatic dual-beam interferometric particle imaging (HADIPI) is adopted to simultaneously measure the three-dimensional (3D) position, velocity and size of spherical metal droplets. We propose to infer the depth displacement of the droplet directly from the angle shift of the interference fringe. Angular cross power spectral density is used to detect the angular shifts of the interference fringe. The depth displacements and velocities can be further obtained from the obtained angular shifts. Proof-of-concept experiments are conducted on micron-sized gallium droplets, demonstrating that the 3D trajectories of the droplets can be accurately obtained, with depth displacement accuracy of tens of microns, improving accuracy in depth position measurement compared to the traditional Lagrangian framework. Different from traditional imaging methods, HADIPI can directly display the 3D movement of droplets, including in the depth direction. In the combustion measurements of the solid rocket motor, the motion state of metal droplets can be precisely determined, demonstrating the feasibility and practicality.

Modification of the Loss Cone for Energetic Particles in the Earth's Inner Magnetosphere

AbstractThe behavior of energetic particles in the Earth's dipole and stretched magnetic‐field models is explored with a focus on the shift of the atmospheric loss cone away from the magnetic‐field direction and on non‐adiabatic behavior occurring when the particle gyroradius becomes comparable with the gradient scale length of the local magnetic field. It is shown that the equatorial loss cone is aberrated away from the magnetic‐field direction (pitch angle of 0°) by the perpendicular drift of a charged particle (which is referred to as the “Mozer transform” described in Mozer (1966, https://doi.org/10.1029/JZ071i011p02701). It is found that the Mozer coordinate transformation in pitch‐angle/gyrophase‐angle space better organizes the behavior of bounce times, mirror altitudes, drift speeds, and first adiabatic invariant. It also describes the loss‐cone shift accurately for a certain range of values of the adiabaticity parameter ϵ, defined by the ratio of the particle gyroradius to the local radius of curvature of the magnetic field. For particles with larger ϵ, the Mozer transform (evaluated with the standard gradient‐curvature drift) breaks down and the “central trajectory” theory can be used to calculate the angular shift of the loss cone, which now includes an Earthward shift. When ϵ becomes relatively large, stochastic field line curvature (FLC) scattering occurs: we show the intimate connection between the strength of FLC scattering and the loss‐cone shift. By comparing ion orbits in the dipole and Tsyganenko (Ts89 and Ts04) magnetic fields, we conclude that the loss cone of ring‐current ions is significantly modified during geomagnetically active times.

Holography with higher-order Stokes correlation

We present and experimentally demonstrate a holography technique with a higher-order Stokes correlation of the random light field. The proposed technique is capable to reconstruct the complex-valued object from the random light field, and overcome twin image issues in the higher-order correlation holography without angular shift, phase shifting, and iterations. A basic principle of the proposed technique is presented and its application is demonstrated by establishing a connection between the higher-order Stokes fluctuations correlations and the far-field complex coherence function of the random field in a lensless configuration. The viability of our technique is demonstrated by considering incoherent reconstruction of the hologram and reconstructing the complex-valued information encoded into the hologram as a distribution of complex coherence function.

Accurate droplet depth displacement measurement with time-resolved astigmatic interferometric particle imaging.

The astigmatic interferometric particle imaging (AIPI) model reveals that the fringe orientation shifts with droplet depth displacement, and their relationships are quantitatively formulated. The depth displacement is directly evaluated from the relative angular shift of the fringes with angular cross power spectral density, and this algorithm isolates the uncertainty of droplet depth position from depth displacement. Proof-of-concept experiments on micrometer-sized transparent droplets with a 5 kHz AIPI system demonstrates that droplet three-dimensional (3D) trajectories are accurately obtained with the accuracy of depth displacement up to tens of micrometers, improving an order of magnitude from hundreds of microns in a traditional Lagrangian framework by comparing droplet depth positions.