Deflection Of Light Rays Research Articles

Weak field deflection angle and analytical parameter estimation of the Lorentz-violating Bumblebee parameter through the black hole shadow using EHT data

Abstract We explored how the Lorentz symmetry breaking parameter $\ell$ affects the Reissner-Nordst"{o}m BH solution in the context of weak field deflection angle, and the black hole shadow. We aim to derive the general expression for the weak deflection angle using the non-asymptotic version of the Gauss-Bonnet theorem, and we presented a way to simplify the calculations under the assumption that the distance of the source and the receiver are the same. \textcolor{blue}{Through the Solar System test, $\ell$ is constrained from around $-10^{-9}$ orders of magnitude to $0$, implying challenging detection of $\ell$ through the deflection of light rays from the Sun.} We also studied the black hole shadow in an analytic way, where we applied the EHT results under the far approximation in obtaining an estimate expression for $\ell$. Using the realistic values of the black hole mass and observer distance for Sgr. A* and M87*, it was shown that $M/r_{\rm o} \neq 1$ is satisfied, implying the relevance and potential promise of the spontaneous Lorentz symmetry breaking parameter's role on the shadow radius uncertainties as measured by the EHT. We find constraints for $\ell$ to be negatively valued, where the upper and lower bounds are $\sim -1.94$ and $\sim -2.04$, respectively.

An overview of light ray deflection calculation by magnetars in nonlinear electrodynamics

Due to the lack of experimental confirmation of the effects of nonlinear electrodynamics (NED) of vacuum on the electromagnetic wave, it remains the most pressing issue. One of the most optimal media for studying these effects, occurring in astrophysics, are magnetars. Various methods of studying the bending of a wave passing through the magnetospheres of magnetars play a key role in a deeper understanding of vacuum NED. This article reviews modern methods for determining the angle of bending of the electromagnetic wave under the effect of NED of vacuum and gravity, with special attention paid to NED of vacuum in intense electromagnetic fields, which is a characteristic feature of magnetars. The article discusses various methods and techniques used to measure these angles, as well as their potential astrophysical applications.

Deflection of light rays in a moving medium around a spherically symmetric gravitating object

Deflection of light rays in a moving medium around a spherically symmetric gravitating object

Imprints of a gravitational wave through the weak field deflection of photons* *A. Ö. and R. P. acknowledge the networking support of the COST Action CA18108 - COST Action CA21106 - COSMIC WISPers in the Dark Universe: Theory, astrophysics and experiments (CosmicWISPers), Quantum gravity phenomenology in the multi-messenger approach (QG-MM), the COST Action CA21136 - Addressing observational tensions in cosmology

In this study, we investigate the novel phenomenon of gravitational lensing experienced by gravitational waves traveling past a Schwarzschild black hole perturbed by a specific, first-order, polar gravitational wave. We apply the Gauss-Bonnet theorem, finding a topological contribution to the deflection of light rays passing near the black hole. We demonstrate that the deflection angle can be determined by analyzing a region entirely outside the path of the light ray, leading to a calculation based solely on the parameters of the perturbing wave (Legendre polynomial order, l; frequency, σ). This approach offers a unique perspective on gravitational lensing and expands our understanding of black hole interactions with gravitational waves.

On the interfacial deformations and thermal characteristics exhibiting self-similar behavior under the action of a line heat source

Interfacial dynamics resulting from a heating source located near the interface play a crucial role in dictating the heat and momentum transport in the near-interface region. This paper aims toward simultaneous characterization of interfacial deformation and thermal behavior under the action of a line heating source placed below the interface. Experiments have been conducted on aqueous glycerol with a heating wire at different power inputs and depths from the interface. The interfacial deformations are mapped and quantified by employing moon-glade background oriented schlieren, which offers real-time, non-intrusive whole field measurements based on the deflection of light rays from liquid interface. Infrared thermography is used to measure transient interfacial temperature variations. Results show that the interface exhibits a convex-shaped deformation under the influence of the heating wire for all cases of heating power and depth. The maximum interface temperature coincides with the peak interfacial deformation. However, the region of thermal influence is smaller compared to the deformed region. Non-dimensionalization of transient interface deformation and temperature profiles establishes the underlying similarity of the phenomenon as non-dimensional interface perturbation profiles overlap for all cases of height and heating power. These characteristics are also observed for normalized temperature profiles at different wire depths.

Weak gravitational lensing by an ESTGB black hole in the presence of a plasma

This paper is devoted to studying the weak-field gravitational lensing properties of a 4D ESTGB black hole, which is surrounded by the plasma medium. The effects of the magnetic charges and the three plasma distribution models in the deflection of light around a 4D ESTGB black hole are investigated in detail. We find that the uniform plasma leads to a larger deflection of light rays in comparison with the singular isothermal sphere (SIS), the non-singular isothermal sphere (NSIS) models. Moreover, the deflection angle increases slightly as the absolute value of the magnetic charge decreases. Finally, we analyze the total magnification of image due to weak gravitational lensing around the black hole. The result shows that the presence of a uniform plasma medium remarkably enhances the total magnification whereas the non-uniform plasma reduces the total magnification.

Three-dimensional reconstruction from a fringe projection system through a planar transparent medium.

A vision measurement system is placed in a protective cover made of a transparent medium to avoid environmental influences. Due to the deflection of light rays on the front and rear surfaces of the transparent medium, the imaging position of an object on the camera target plane is deviated, which makes the traditional vision detection methods based on the triangulation principle produce large measurement errors. This work introduces a three-dimensional (3D) reconstruction method by fringe projection system through a planar transparent medium. We derive the coordinate transformation relationship between a real-object point and a pseudo-object point caused by light refraction based on Snell's law of flat refraction. Based on the relationship, a modified fringe projection method is proposed for unbiased 3D reconstruction. Two experiments, including 3D shape measurement of a white plate with ring markers and 3D shape measurement of a regular spherical object are conducted. The results demonstrate the effectiveness of the proposed method in such measurement environment.

Evolutionary background-oriented schlieren tomography with self-adaptive parameter heuristics.

For volumetric reconstruction of the refractive index field in a flow, background-oriented schlieren (BOS) imaging which measures the deflection of light rays due to refractive index variations is combined with an evolutionary tomographic algorithm for the first time, called evolutionary BOS tomography (EBOST). In this work application to reactive flows is presented. Direct non-linear ray-tracing of the reconstruction domain is used to evaluate the fitness of solution candidates during the evolutionary strategy that was implemented to run on a multi-GPU system. The use of a diversity measure and its consideration in a migration policy was tested against a simple scheme that distributes the best chromosome (solution candidate) in an island-based genetic algorithm. The extensive set of control parameters of the presented algorithm was harnessed by a self-adaptive strategy taking into account the fitness function and operator rates. Quantitative characterisation of the EBOST via numerical phantom studies, using flame simulations as ground truth data is presented. A direct comparison to a state-of-the-art BOST algorithm demonstrates similar accuracy for a turbulent swirl flame phantom reconstruction. A series of experimental applications of the EBOST on several unsteady and turbulent flames is also presented. In all cases, the instantaneous and time-averaged flame structure is revealed, proving the benefit of EBOST for volumetric flow diagnostics.

Deflection light behaviors by AdS black holes

We investigate the behavior of the deflection of light rays by charged and rotating AdS black holes using the Gauss–Bonnet formalism. Taking weak field approximations and certain appropriate limits associated with AdS geometries, we compute and analyze such an optical quantity by varying the involved moduli space parameters. First, we study the charge and the AdS radius effects on the deflection angle of RN-AdS black holes. For small values of the impact parameter b, we find that the charge effect is relevant. Precisely, it decreases the deflection angle, while the AdS background one is not. For large values of b, however, these optical behaviors have been inverted and the deflection angle becomes an increasing function of the charge. In this way, the cosmological constant effect is remarked to be relevant showing linear variations of the deflection angle. Varying the charge, we find a critical impact parameter value \(b_{c}\) where the charge effect is inverted. For rotating solutions, we show that the spinning parameter still decreases the deflection angle without any changing behavior observed in the charge effect. Evincing of the cosmological constant, we recover known results corresponding to charged and rotating ordinary black hole solutions. Examining the plasma effect, we reveal that the deflection angle keeps the same behavior being a decreasing function in terms of the frequency ratio.

New transform to project axisymmetric deflection fields along arbitrary rays

Axisymmetric tomography is used to extract quantitative information from line-of-sight measurements of gas flow and combustion fields. For instance, background-oriented schlieren (BOS) measurements are typically inverted by tomographic reconstruction to estimate the density field of a high-speed or high-temperature flow. Conventional reconstruction algorithms are based on the inverse Abel transform, which assumes that rays are parallel throughout the target object. However, camera rays are not parallel, and this discrepancy can result in significant errors in many practical imaging scenarios. We present a generalization of the Abel transform for use in tomographic reconstruction of light-ray deflections through an axisymmetric target. The new transform models the exact path of camera rays instead of assuming parallel paths, thereby improving the accuracy of estimates. We demonstrate our approach with a simulated BOS scenario in which we reconstruct noisy synthetic deflection data across a range of camera positions. Results are compared to state-of-the-art Abel-based algorithms. Reconstructions computed using the new transform are consistently more stable and accurate than conventional reconstructions.

Deflection of light rays by a spherically symmetric black hole in a dispersive medium

The influence of the medium on the gravitational deflection of light rays is widely discussed in literature for the simplest non-trivial case: cold non-magnetized plasma. In this article, we generalize these studies to the case of an arbitrary transparent dispersive medium with a given refractive index. We calculate the deflection angle of light ray moving in a general spherically symmetric metric in the presence of medium with the spherically symmetric refractive index. The equation for the radius of circular light orbits is also derived. We discuss in detail the properties of these results and various special cases. In particular, we show that multiplying the refractive index by a constant does not affect the deflection angle and radius of circular orbits. At the same time, the presence of dispersion makes the trajectories different from the case of vacuum even in spatially homogeneous medium. As one of the applications of our results, we calculate the correction to the angle of vacuum gravitational deflection for the case when a massive object is surrounded by homogeneous but dispersive medium. As another application, we present the calculation of the shadow of a black hole surrounded by medium with arbitrary refractive index. Our results can serve as a basis for studies of various plasma models beyond the cold plasma case.

Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target.

Digital gradient sensing (DGS) is a non-contact and full-field optical measurement technique, which assesses mechanical behaviors of transparent materials or specular structures by measuring angular deflections of light rays. However, owing to the poor light-gathering capability of its imaging system, the dynamic performance of DGS is heavily restricted. Here, a method of enhancing the dynamic performance of DGS by improving its speckle target is proposed. The method employs the technique of backlight illumination, which significantly increases the utilization efficiency of light, shortens the exposure time, and enhances the dynamic performance of DGS. Additionally, it also uses the optimized digital speckle pattern to improve the measurement precision and accuracy. For validation, a comparison experiment was conducted, proving that the proposed method can improve the utilization efficiency of light by about 80 times and improve the quality of the speckle images by about 40%. Real tests, including a uniaxial tension test using transmission-mode DGS (t-DGS) and a three-point bending test using reflection-mode DGS (r-DGS), were also carried out, showing the efficacy and high compatibility of the proposed backlight digital speckle target. In summary, this simple method greatly improves the performance of DGS, which can be used as a standard method in both t-DGS and r-DGS.

One hundred years of testing general relativity: from Eddington’s eclipse to general relativistic MHD

In 1919, the observation during a solar eclipse of the deflection of light rays from stars near the Sun decreed the validity of Einstein’s general relativity. One hundred years later, the image of the black hole M87* by the Event Horizon Telescope collaboration proved the existence of these fascinating objects on the one hand, and on the other, the validity of general relativistic magnetohydrodynamics (GRMHD) in the strong gravity regime. Numerical simulations have been used to model the accreting plasma around the black hole, whose emission is at the base of the synthetic images compared with data. Here, we briefly discuss the methods and the initialization employed for these simulations, and we briefly report the results of GRMHD axisymmetric simulations where a dynamo mechanism operates inside the disk, enhancing the magnetic field from its initial seed values up to those needed to explain the observed plasma emission.

On long range axion hairs for black holes

The physics of black holes can suggest new ways to test the existence of axions. Much work has been done so far to analyse the phenomenon of superradiance associated with axions in the ergoregion surrounding rotating black holes. In this work, we instead investigate how Chern–Simons axion couplings of the form and , well motivated by particle physics and string theory, can induce long range profiles for light axion fields around charged black holes, with or without spin. We extend known solutions describing axion hairs around spherically symmetric, asymptotically flat dyonic black hole configurations, charged under gauge symmetries, by including non-minimal couplings with gravity. The axion acquires a profile controlled by the black hole conserved charges, and we analytically determine how it influences the black hole horizon and its properties. We find a Smarr formula applying to our configurations. We then generalise known solutions describing axion hairs around slowly rotating black hole configurations with charge. To make contact with phenomenology, we briefly study how long range axion profiles induce polarised deflection of light rays, and the properties of ISCOs for the black hole configurations we investigate.

Study of gravitational deflection of light ray

Gravitational deflection of light ray is one of the famous predictions of Einstein’s general theory of relativity. The deflection of light ray, as it passes around a gravitational mass, can be calculated by different methods such as null geodesics method and material medium approach. In this paper a comparative study will be done for gravitational deflection of light ray, calculated by different authors using different methods. In this study, different gravitating body such as static, rotating and charged body will be considered which are represented by Schwarzschild metric, Kerr metric, Reissner-Nordström metric and Janis-Newman-Winicour metric.

Underwater Dynamic Visual Servoing for a Soft Robot Arm With Online Distortion Correction

Bioinspired soft robots have generated increasing attentions due to their optimal performance in specific environments stemming from their unique morphology and sensorimotor capabilities. This also raises new challenges in modeling and control due to their unconventional soft mechanism. In this paper, we aim to improve the controllability of an octopus tentacle-like soft robot arm operating in an underwater environment and to reproduce the perception-guided tracking performance of its biological counterpart when preying on and pursuing a target. To this end, we design an adaptive visual servoing controller for trajectory tracking tasks, taking into account system dynamics with environment interactions. Unlike on-the-ground visual servoing controller, the underwater environment exerts multirefraction effects on the image projection process, increasing difficulties in obtaining an accurate camera projection model. This paper thus proposes an adaptive method that can online correct image distortion caused by the deflection of light rays passing through different mediums to compensate for refraction effects. The adaptive algorithm can simultaneously estimate unknown camera parameters to completely avoid complex offline underwater camera calibration. The proposed adaptive controller validates the trajectory tracking performance experimentally and position and image velocity.

Volumetric calibration enhancements for single-camera light-field PIV

This work presents a volumetric calibration method for single-camera light-field particle image velocimetry (light-field PIV or LF-PIV). The proposed technique makes use of the unique point-like feature of particle light-field images to accurately determine affected pixels for a spatial voxel over a relative large measurement volume. A calibration model is derived based on Gaussian optics, which relates a spatial point light source with its confusion circle produced on microlens array (MLA), and optical distortions are accounted for by introducing five calibration parameters. By taking lens defects and misalignment between MLA and image sensor into account, the calibration method can calculate weighting coefficient for particle image reconstruction more accurately than the theoretical ray-tracing method, especially for regions further away from focal plane where light ray deflections are significant due to optical distortions. The volumetric calibration method was validated by simulation tests using synthetic light-field images, and has been successfully applied to a classic vortex-ring LF-PIV measurement, where the measurable range in depth direction was successfully extended and the quality of reconstructed volumetric velocity field was greatly improved.

Fracture behavior of carbon fiber reinforced polymer composites: An optical study of loading rate effects

Crack initiation and growth in single-edge notched unidirectional T800s/3900-2 CFRP laminates are studied under stress wave and quasi-static loading conditions. An optical technique called reflection-mode Digital Gradient Sensing is also extended to study fracture mechanics of CFRP by using it in conjunction with ultrahigh-speed photography to perform full-field measurement of crack-tip deformations in the pre- and post-crack initiation regimes. DGS is capable of measuring two orthogonal surface slopes in the crack-tip vicinity as angular deflection of light rays. A method for extracting crack-tip parameters – the instantaneous crack speed and stress intensity factor (SIF) histories – associated with the stationary and propagating cracks using measured surface slopes is presented. The effect of fiber orientation in the range 0°–60° relative to the initial notch and two loading rates are investigated. Nominally mode-I fracture occurs when the fiber orientation is 0° whereas mixed-mode fractures ensue in others. Besides crack initiation occurrence at higher loads as fiber orientation increases, the SIF histories imply strong fiber bridging at low fiber orientations under quasi-static conditions. Furthermore, this CFRP shows significant loading rate dependence during crack growth. Unlike stress wave loading conditions, an increasing crack growth resistance immediately after crack initiation is seen under quasi-static conditions.

Reconstruction method of axisymmetric refractive index fields with background-oriented schlieren.

A refractive index field can be quantitatively visualized by using a background-oriented schlieren (BOS) technique to measure the displacements of background dot patterns of a 2D image captured by a camera. In BOS, the displacement is caused by the deflection of the light ray passing through the refractive index field. However, obtaining depth information of refractive index fields is often difficult because dot-pattern displacement results from deflection of light rays integrated over their path. A method of reconstructing depth information of the refractive index field using an inverse matrix method with the BOS technique is proposed here under the assumption of an axisymmetric refractive index field. A field, generated by laser irradiation inside a glass, is reconstructed by the proposed method and is also theoretically calculated using the heat diffusion equation and thermal stress theory. The reconstructed field agrees well with the theoretically calculated one, which validates the proposed method. The proposed method is a promising candidate for measuring axisymmetric refractive index fields of various media.

Measurement of Sub-micron Deformations and Stresses at Microsecond Intervals in Laterally Impacted Composite Plates Using Digital Gradient Sensing

Visualization and quantification of surface topography and stresses from measured slope data is of considerable importance to study many engineering problems including response of structural plates to stress wave loading. In this work, a full-field optical technique called Digital Gradient Sensing (DGS) is implemented in the reflection-mode to quantify time-resolved surface slopes in composite plates at microsecond intervals as they are impact loaded. The method being capable of determining two orthogonal surface slopes by measuring angular deflections of light rays, as small as a few micro-radians, surface topography can be quantified using a Higher-order Finite-difference-based Least-squares Integration (HFLI). Numerical differentiation of surface slopes, on the other hand, provides all three curvatures enabling estimation of stresses. Carbon fiber reinforced composite plates of different layups are subjected to dynamic impact loading using a Hopkinson pressure bar. Ultrahigh-speed digital photography is used to record deformations using DGS. The out-of-plane deformations are obtained by post-processing data from DGS at each time instant using HFLI whereas stresses are estimated by evaluating instantaneous curvatures obtained by differentiating measured slopes.