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Piezoresponse Force Microscopy (PFM) is capable of detecting strains in piezoelectric materials down to the picometer range. Driven by diverse application areas, numerous weaker electromechanical materials have emerged. The smaller signals associated with them have uncovered ubiquitous crosstalk challenges that limit the accuracy of measurements and that can even mask them entirely. Previously, using an interferometric displacement sensor (IDS), we demonstrated the existence of a special spot position immediately above the tip of the cantilever, where the signal due to body-electrostatic (BES) forces is nullified. Placing the IDS detection spot at this location allows sensitive and BES artifact-free electromechanical measurements. We denote this position as x I D S / L = 1 , where x I D S is the spot position along the cantilever and L is the distance between the base and tip. Recently, a similar approach has been proposed for BES nullification for the more commonly used optical beam deflection (OBD) technique, with a different null position at x O B D / L ≈ 0.6 . In the present study, a large number of automated, sub-resonance spot position dependent measurements were conducted on periodically poled lithium niobate. In this work, both IDS and OBD responses were measured simultaneously, allowing direct comparisons of the two approaches. In these extensive measurements, for the IDS, we routinely observed x I D S / L ≈ 1 . In contrast, the OBD null position ranged over a significant fraction of the cantilever length. Worryingly, the magnitudes of the amplitudes measured at the respective null positions were typically different, often by as much as 100%. Theoretically, we explain these results by invoking the presence of both BES and in-plane forces electromechanical forces acting on the tip using an Euler–Bernoulli cantilever beam model. Notably, the IDS measurements support the electromechanical response of lithium niobate predicted with a rigorous electro-elastic model of a sharp PFM tip in the strong indentation contact limit [ d e f f ≈ 12 pm / V , Kalinin et al., Phys. Rev. B 70, 184101 (2004)]. [ABSTRACT FROM AUTHOR]

We have studied diffusion and thermodiffusion in the ternary system polystyrene + toluene + cyclohexane over the entire composition range of the binary solvent toluene + cyclohexane and for polymer concentrations up to 0.1 mass fractions by multi-color optical beam deflection. The polystyrene molar masses were 4.88 and 17.90 kg/mol. The inversion problem of the contrast factor matrix could be avoided by reasonable a priori assumptions about the diffusion eigenvectors. The fast mode of the bimodal dynamics is attributed to the interdiffusion of the two solvents at constant polymer concentration, whereas the slow mode is due to the diffusion of the polymer with respect to the binary solvent. The amplitude of the fast mode vanishes in the pure toluene and the pure cyclohexane limits of the mixed solvent. The amplitude of the slow mode increases with polymer concentration. The composition and temperature dependence of the slow diffusion eigenvalue, the hydrodynamic correlation length, and the Soret coefficient of the polymer reflect the transition from a good to a theta solvent with increasing cyclohexane content and with decreasing temperature. Due to cross diffusion, cyclohexane reverses its migration direction between the fast and the slow mode, leading to a positive thermodiffusion but a negative Soret coefficient. The polymer thermodiffusion coefficients during the slow mode vary by approximately a factor of two, depending on the solvent composition. Rescaling with the solvent viscosity collapses all data onto a single master curve with an extrapolated value of ηDT ≈ 6 × 10−15 Pa m2 K−1 in the dilute limit. This value is well known from various other binary polymer/solvent mixtures. [ABSTRACT FROM AUTHOR]

In this paper, we construct a Schwarzschild metric in the fractal dimension based on fractal calculus, and we study the deflection of light near the sun. It was observed that the new fractal spherically symmetric spacetime metric may describe supermassive black holes, which have been detected through various astronomical observations such as SDSS. We have discussed the deflection of light by the gravitational field of the sun. It was observed that the total deflection of light is affected by the fractal dimension. To estimate the numerical value of the fractal dimension, we have used the 2004analysis of almost 2 million VLBI observations of 541 radio sources made by 87 VLBI sites, which estimates the factor γ based on PNN formalism. It was observed that the fractal dimension is roughly less than unity. However, our analysis showed that large bending gravity gives fractal dimensions lower than unity to some extent. We also gave a naïve idea about the emission thermal Unruh process in fractal dimension. It was observed that both the temperature and the entropy of black holes are affected by the fractal dimension, and that for low numerical values, the entropy of the black hole is enhanced. [ABSTRACT FROM AUTHOR]

In this paper, a comparative study of the mode-I fracture behaviors of two types of specimens with a V-notch defect under plane stress conditions was performed using the digital gradient sensing (DGS) method. First, two types of specimens (namely one-piece specimen and bonded specimen) with the same V-notch defect were both made of polymethyl methacrylate (PMMA), and three different V-notch angles' defect were considered for each type of specimen. Then, three-point bending tests were performed on both types of specimens. The angular deflection field of light near the V-notch region was recorded using a CCD during the experiments. Finally, by utilizing the relationship between the stress gradient and angular deflection as established by the elasto-optic effect, in conjunction with the principles of linear elastic fracture mechanics theory, the stress intensity factors (SIFs) of two types of specimens under different stress conditions were calculated using the least square method. According to the experimental results, the influence of V-notch angle on fracture load and fracture toughness of two kinds of specimens was discussed. Meanwhile, the experimental results show the significant differences in the fracture behaviors of the two types of specimens under mode-I loading conditions. [ABSTRACT FROM AUTHOR]

Polarizing beam splitters (PBSs) are fundamental components of optical systems and are crucial for sensing, communication, and imaging tasks. Traditional PBS devices, assembled using right-angle prisms with dielectric coatings, face challenges such as bulkiness and limited versatility in deflection directions. To address these limitations, we meticulously make metasurfaces for enhanced PBS performance. Metasurfaces, composed of subwavelength structures, manipulate wavefronts, polarization, and light intensity. Using metasurfaces in the design of PBS devices, we can precisely tailor the structure to manipulate the deflection angles of light beams, ensuring that they align with the desired specifications. Our experimental results closely align with simulation outcomes, showcasing deflection angles of a 1.5 mm diameter metasurface near ±15 degrees for s- and p-polarizations in a wavelength of 940-nm. [ABSTRACT FROM AUTHOR]

In this paper, an innovative approach is introduced to address the noise issues associated with micro–cantilever array deflection measurement systems employing multiple lasers. Conventional systems are affected by laser mode hopping during switching, resulting in wavelength instability and beam spot fluctuations that take several hundred milliseconds to stabilize. To mitigate these limitations, a high–speed laser modulation technique is utilized, leveraging the averaging effect over multiple modulation cycles within the sampling window. By driving the lasers with a high–frequency carrier signal, a low–noise and stable output suitable for micro–cantilever beam deflection measurement is achieved. The effectiveness of this approach is demonstrated by simultaneously modulating the lasers and rapidly observing the spectral and centroid variations during high–speed switching using a custom–built high–speed spectrometer. The centroid fluctuations are also analyzed under different modulation frequencies. The experimental results confirm that the high–speed modulation method can reduce the standard deviation of beam spot fluctuations by more than 90%, leading to significant improvements in noise reduction compared to traditional laser switching methods. The proposed high–speed laser modulation approach offers a promising solution for enhancing the precision and stability of multi–laser micro–cantilever array deflection measurement systems. [ABSTRACT FROM AUTHOR]

Microcantilever arrays are valuable tools for detecting minute physical and chemical changes. Traditional microcantilever array systems, including our previous work utilizing multiple laser arrays, frequently encounter high complexity, significant costs, and increased noise caused by laser switching. This study introduces a refraction-based laser scanning system that significantly mitigates these issues by employing a rotating glass optical block for multiplex scanning. This innovative approach not only simplifies the scanning process by eliminating the need to move the laser source or the microcantilever array but also enhances scanning speed and reduces noise, as demonstrated by our experiments. Overall, this research implements a new optical scanning strategy for microcantilever array systems, which is promising due to its direct application potential as it paves the way for more accurate, high-performing, and cost-effective sensing solutions. [ABSTRACT FROM AUTHOR]

The purpose of this review is to analyze the trend in optical features and flexibility changes of flexible ureteroscopes over the past decades, and determine the correlation of individual parameters with release period as well as with dimensional parameters. Flexible ureteroscopes mentioned in the literature or those commercially available were searched. To minimize the search bias, the instruments were grouped by release date time-periods of < 2000 year, 2000–2009, 2010–2019, and 2020 onwards. The final review included only those instrument models for which data on minimum and maximum depth of field, field of view, direction of view, and deflection degree had been determined. The correlation among features investigated as well as with release period was also determined. 61 models of flexible ureteroscopes (27 fibreoptic and 34 digital scopes) were included. Among the different features investigated among fiberoptic endoscopes, minimum depth of field positively and negatively correlated with channel size and field of view, respectively, whereas maximum depth of view and field of view positively correlated with overall shaft and deflection degree, respectively. Up and down deflection strongly correlated with each other and both were negatively proportional to the distal tip size. For the digital endoscopes, minimum depth of field negatively and positively correlated with distal tip size and working length, respectively. Maximum depth of field positively correlated with field of view, whereas the latter was negatively proportional to the overall shaft. As for the fiberoptic counterparts, up and down deflection strongly correlated with each other. Field of view, up and down deflection of fiberoptic flexible ureteroscopes, were significantly increased among fiberoptic and digital endoscopes over decades. As flexible ureteroscopy technology has evolved, there has been a trend towards increasing field of view with up and down deflection. Given the importance of scope ergonomics, one aspect of this popularity is the improvement of optical characteristics and deflection degree, which significantly correlates with the release period. [ABSTRACT FROM AUTHOR]

In this paper, we analyze weak gravitational lensing by taking the black hole solution in Einstein Cubic gravity with the Gibbons and Werner approach. We deduce the deflection angle of light in a nonplasma and plasma medium. Firstly, we derive the Gaussian optical curvature and apply the Gauss–Bonnet theorem to find the deflection angle for the black hole spherically symmetric space–time. Additionally, we examine the graphical behavior of the deflection angle caused by the black hole in the presence of the nonplasma and plasma medium. Further, we use Einstein cubic gravity black hole geometry to discuss the quasi-periodic oscillations, effective force, and emission energy. [ABSTRACT FROM AUTHOR]

It has long been known that galaxy shapes align coherently with the large-scale density field. Characterizing this effect is essential to interpreting measurements of weak gravitational lensing, the deflection of light from distant galaxies by matter overdensities along the line of sight, as it also produces coherent galaxy alignments that we wish to interpret in terms of a cosmological model. Existing direct measurements of intrinsic alignments using galaxy samples with high-quality shape and redshift measurements typically use well-understood but sub-optimal projected estimators, which do not make good use of the information in the data when comparing those estimators to theoretical models. We demonstrate a more optimal estimator, based on a multipole expansion of the correlation functions or power spectra, for direct measurements of galaxy intrinsic alignments. We show that even using the lowest order multipole alone increases the significance of inferred model parameters using simulated and real data, without any additional modelling complexity. We apply this estimator to measurements of parameters of the non-linear alignment model using data from the Sloan Digital Sky survey, demonstrating consistent results with a factor of ∼2 greater precision in parameter fits to intrinsic alignments models. This result is functionally equivalent to quadrupling the survey area, but without the attendant costs – thereby demonstrating the value in using this new estimator in current and future intrinsic alignments measurements using spectroscopic galaxy samples. [ABSTRACT FROM AUTHOR]

Linearized differential equations appear in this article in the context of light and particle deflection in Schwarzschild spacetime, the simplest metric solution of Einstein's equations. The procedures can be easily employed in upper level undergraduate courses, and the results illustrate the frequent failure of the Einstein equivalence principle in predicting deflection due to spatial curvature. The full geodesic equations are themselves readily accessible, but they need not necessarily be derived or addressed in order for students to gain an appreciation of the limited validity of equating particle motion in an accelerating Lorentz frame of reference to motion under the influence of Newtonian gravity. We show by direct calculation that the common equivalence principle explanation for why gravity must deflect light is quantitatively incorrect by a factor of three in Schwarzschild geometry. It is, therefore, possible, at least as a matter of principle, to tell the difference between local acceleration and a true gravitational field by measuring the local deflection of light. We calculate as well the deflection of test particles of arbitrary energy and construct a leading-order coordinate transformation from Schwarzschild to local inertial coordinates, which shows explicitly how the effects of spatial curvature manifest locally for relativistic trajectories of both finite and vanishing rest mass particles. [ABSTRACT FROM AUTHOR]

The refractive index of a liquid serves as a fundamental parameter reflecting its composition, thereby enabling the determination of component concentrations in various fields such as chemical research, the food industry, and environmental monitoring. Traditional methods for refractive index (RI) measurement rely on light deflection angles at interfaces between the liquid and a material with a known refractive index. In this paper, the authors present a new differential refractometer for the highly sensitive measurement of RI differences between two liquid samples. Using a configuration with two cells equipped with flat parallel plates as measuring elements, the instrument facilitates accurate analysis. Namely, the sensor signals from both the solution and the solvent cuvette are generated simultaneously with one laser pulse, reducing the possible fluctuations in the laser radiation intensity. Our evaluation shows the high sensitivity of RI measurements < 7 × 10 − 6 ), so this differential refractometer can be proposed not only as a high-sensitivity sensing tool that can be used for mobile detection of nanoparticles in solution samples but also to determine the level of environmental nano-pollution using water (including rain, snow) samples from various natural as well as industrial sources, thus helping to solve some important environmental problems. [ABSTRACT FROM AUTHOR]

As one of the most common spatial light modulators, linear micromirror arrays (MMAs) based on microelectromechanical system (MEMS) processes are currently utilized in many fields. However, two crucial challenges exist in the fabrication of such devices: the adhesion of silicon microstructures caused by anodic bonding and the destruction of the suspended silicon film due to residual stress. To solve these issues, an innovative processing method assisted by temporary anchors is presented. This approach effectively reduces the span of silicon microstructures and improves the Euler buckling limit of the silicon film. Importantly, these temporary anchors are strategically placed within the primary etching areas, enabling easy removal without additional processing steps. As a result, we successfully achieved wafer-level, high-yield manufacturing of linear MMAs with a filling factor as high as 95.1%. Demonstrating superior capabilities to those of original MMAs, our enhanced version boasts a total of 60 linear micromirror elements, each featuring a length-to-width ratio of 52.6, and the entire optical aperture measures 5 mm × 6 mm. The linear MMA exhibits an optical deflection angle of 20.4° at 110 Vdc while maintaining exceptional deflection flatness and uniformity. This study offers a viable approach for the design and fabrication of thin-film MEMS devices with high yields, and the proposed MMA is promising as a replacement for digital micromirror devices (DMDs, by TI Corp.) in fields such as spectral imaging and optical communication. [ABSTRACT FROM AUTHOR]

The necessity of minimizing NOx emissions drives the pursuit of ultra-lean premixed combustion in aeroengines and gas turbines, characterized by susceptibility to combustion instabilities. To tackle this issue, swirling flow design is widely incorporated into lean premixed combustor design, enhancing flame stability, and shortening flame length. This study utilizes the tomographic background-oriented Schlieren (TBOS) to reconstruct the spatial distribution of the refractive index gradient of lean premixed turbulent swirl flames with an aeroengine combustor configuration. A parametric study of the TBOS reconstruction quality is conducted, and the results reveal that view sparseness primarily degrades the reconstruction quality compared to the specific iterative algorithm used. The classic visual hull approach is explored to address this challenge, highlighting the significance of visual hull size. Furthermore, to improve the reconstruction quality, a posterior support constraint method is proposed, involving the removal of voxels of nearly constant refractive index within the central volume surrounded by flames. Results demonstrate that implementing this posterior support constraint further improves the reconstruction quality of lean premixed turbulent swirl flames. Finally, the robustness of this posterior support constraint method is validated by introducing high-level noise to the light deflection data, showcasing the potential of combining the dedicated designed visual hull and proposed posterior support constraint in addressing the view sparseness challenge for TBOS measurements. [ABSTRACT FROM AUTHOR]

We study here a novel application of Kim and Lee charged wormholes assuming them to be dark halo objects playing the role of lenses in the Galactic microlensing with source stars belonging to the Galactic Bulge and the Large Magellanic Cloud. First, we observe that both the backreacted scalar (α ) and electrically (Q) charged wormholes have the same zero ADM mass as has the background Ellis–Bronnikov wormhole having a special equation of state parameter γ = - 1 . In particular, we argue that, for α ≠ 0 , the solution formally resembles, but can at best be sourcewise different from, that of the background wormhole. The charge ( Q ≠ 0 ) thus provides an extra degree of freedom that introduces a non-trivial redshift function Φ to the background, alters its throat radius to r th , yet keeps the wormhole massless. Second, we focus on this electrically charged case and calculate the light deflection angle up to 4th PPN order, analyze the effect of Q on the lensing observables such as the image positions, magnification, centroid and time delay of images of the source stars. Third, we analyze the probabilistic features such as optical depth and event rate estimated on the basis of the hypothesis that the wormhole lens could be bound or unbound to our Galaxy. Finally, we report an intriguing qualitative prediction that, compared to the Schwarzschild black hole, the Paczyński light curves of the electrically charged wormhole are much dimmer that also show characteristic gutters at the times the source enters and exits the Einstein ring. The gutters gradually come together as Q approaches the extreme limit r th 2 , at which the Einstein radius R E vanishes so that the source crosses it instantly. It is speculated that re-analyzing past data on Galactic microlensing may betray the presence of charged wormholes. [ABSTRACT FROM AUTHOR]

The study of phoretic transport phenomena under non-stationary conditions presents several challenges, mostly related to the stability of the experimental apparatus. This is particularly true when investigating with optical means the subtle temperature and concentration fluctuations that arise during diffusion processes, superimposed to the macroscopic state of the system. Under these conditions, the tenuous signal from fluctuations is easily altered by the presence of artifacts. Here, we address an experimental issue frequently reported in the investigation by means of dynamic shadowgraphy of the non-equilibrium fluctuations arising in liquid mixtures under non-stationary conditions, such as those arising after the imposition or removal of a thermal stress, where experiments show systematically the presence of a spurious contribution in the reconstructed structure function of the fluctuations, which depends quadratically from the time delay. We clarify the mechanisms responsible for this artifact, showing that it is caused by the imperfect alignment of the sample cell with respect to gravity, which couples the temporal evolution of the concentration profile within the sample with the optical signal collected by the shadowgraph diagnostics. We propose a data analysis protocol that enables disentangling the spurious contributions and the genuine dynamics of the fluctuations, which can be thus reliably reconstructed. The imposition of a thermal gradient across a liquid mixture results in a time-dependent refractive index distribution. In the presence of a misalignment of the confining cell with respect to gravity, this leads to a deflection of the optical probe beam used to monitor concentration fluctuations within the sample in quantitative shadowgraphy experiments. If not properly accounted for, this effect can introduce a significant bias in the optical signal. [ABSTRACT FROM AUTHOR]

Two-color optical measurements of thermodiffusion in ternary mixtures frequently suffer from ill-conditioned contrast factor matrices, whose inversion leads to very large experimental errors. In this contribution, we show how the error amplification can be avoided in situations where a priori knowledge about the directions of the eigenvectors of the diffusion matrix is available. We present optical beam deflection experiments on solutions of the polymer polystyrene of Mw = 4880 g/mol in a mixed solvent of toluene and cyclohexane. In this system, the two diffusion eigenvalues differ by almost one order of magnitude. The large eigenvalue can be attributed to the interdiffusion of the two solvents and the small one to the polymer diffusion relative to the mixed solvent. The pre-selection of the eigenvectors renders the method stable against fluctuations of the experimental parameters. Both the diffusion and the Soret coefficients attributed to the two modes agree very well with the respective values of corresponding binary mixtures. [ABSTRACT FROM AUTHOR]

Gravitational lensing is a general relativistic (GR) phenomenon where a massive object redirects light, deflecting, magnifying, and sometimes multiplying its source. We use reaction-diffusion (RD) Belousov-Zhabotinsky (BZ) chemistry to study this astronomical effect in a table-top experiment. We experimentally observe BZ waves passing through non-planar, quasi-two-dimensional molds and reproduce the waveforms in computer simulations using planar RD waves propagating with variable diffusion. We tune the variable diffusion to match the Schwarzschild-coordinate light speed near a spherical mass so the RD propagation approximates Einstein's famous light deflection relation. We discuss varying the diffusion or reaction rates with a gel matrix or with illumination, electric field, or temperature gradients. [ABSTRACT FROM AUTHOR]

Light bending is one of the classical tests of general relativity and is a crucial aspect to be taken into account for accurate assessments of photon propagation. In particular, high-precision astrometry can constrain theoretical models of gravitation in the weak field limit applicable to the Sun neighborhood. We propose a concept for experimental determination of the light deflection close to the Sun in the 10 − 7 to 10 − 8 range, in a modern rendition of the 1919 experiment by Dyson, Eddington and Davidson, using formation flying to generate an artificial long-lasting eclipse. The technology is going to be demonstrated by the forthcoming ESA mission PROBA3. The experimental setup includes two units separated by 150 m and aligned to the mm level: an occulter and a small telescope (0.3 m diameter) with an annular field of view covering a region 0 ∘. 7 from the Sun. The design is compatible with a space weather payload, merging several instruments for observation of the solar corona and environment. We discuss the measurement conditions and the expected performance. [ABSTRACT FROM AUTHOR]

The background oriented schlieren (BOS) imaging relies on measuring the light deflection angle in proportion to the refractive index gradient due to the change in the density of a medium. BOS imaging is sensitive to light deflection, and the quantitative measurement requires a reliable calibration method. It is convenient to calibrate the BOS based on the measurement of light deflection. All current BOS calibrations use the random dot as the background and digital image correlation (DIC) as the processing algorithm. Such calibrations can induce an inaccurate measurement. This paper proposes a new method to calibrate the BOS based on measuring a known light deflection angle of a wedge prism. The proposed method uses a fringe pattern instead of the random-dot and works based on phase demodulation. The fringe patterns are phase modulated by the wedge prism (the schlieren object). The demodulation utilizes the Hilbert transform (HT) on the BOS images, giving the phase difference of the images. The BOS converts the phase difference into the deflection angle. The calibration relies on the deviation of the angle measured by the BOS with the known angle of a wedge prism. The results show that the measurement accuracy of the BOS can achieve more than 95%. This result shows high accuracy in measuring the light deflection angle. Also, the proposed method is more accurate than other methods, and fringe patterns outperform random dot patterns in BOS imaging. Soon, this proposed calibration method can be adopted to validate the instruments for measuring the physical properties of a transparent medium in two-dimensional (2-D) visualization, in a contactless and non-intrusive manner. [ABSTRACT FROM AUTHOR]

The topic of gravitational lensing in the Mannheim–Kazanas solution of Weyl conformal gravity and the Schwarzschild–de Sitter solution in general relativity has featured in numerous publications. These two solutions represent a spherical massive object (lens) embedded in a cosmological background. In both cases, the interest lies in the possible effect of the background non-asymptotically flat spacetime on the geometry of the local light curves, particularly the observed deflection angle of light near the massive object. The main discussion involves possible contributions to the bending angle formula from the cosmological constant Λ in the Schwarzschild–de Sitter solution and the linear term γ r in the Mannheim–Kazanas metric. These effects from the background geometry, and whether they are significant enough to be important for gravitational lensing, seem to depend on the methodology used to calculate the bending angle. In this paper, we review these techniques and comment on some of the obtained results, particularly those cases that contain unphysical terms in the bending angle formula. [ABSTRACT FROM AUTHOR]

In the present work, we solve the nonlinear Helmholtz differential equation by means of the Jacobi elliptic functions in the context of the problem of the deflection of light in the gravitational field of the Sun and taking into account the cosmological constant in the Einstein equations. The proposed methodology can be of great help for students and researchers who are starting the study of nonlinear problems and their applications. [ABSTRACT FROM AUTHOR]

The study investigated the variations in luminance of active‐matrix organic light‐emitting diodes (AMOLED) when viewed at small angles, employing different micro lens arrangements. By examining the micro lens array (MLA) structure, we analyzed how luminance behaves at various angles. Concurrently, we explored the alignment of red, green, and blue (R/G/B) pixel apertures with the micro lens placement, aiming to achieve precise luminance modulation for acute viewing angles. Initially, micro lens arrays are crafted by utilizing materials with varying refractive indices above the pixel aperture, ensuring total internal reflection of light at thejunction between materials of high and low refractive indices. This arrangement also alters the emission angle of light. Within this architecture, the critical angle — determined by the disparity in refractive indices — and the variance in the angle at the reflective interface are crucial in influencing light emission reflection. Furthermore, we explored how the spacing of graphic openings with low refractive indices influences the angle of light emission. This spacing affects the reflection angle, as it is not produced by a singular interface but rather by a composite of multiple angles. The size of the pixel apertures and the spacing of these openings cause the point of total internal reflection to vary, altering the deflection angle of light. Thus, the design of pixel openings and the external expansion is crucial to controlling the light emission angle. Lastly, we examined the influence of the reflective interface and the external expansion design on the light output angle. This analysis highlighted the enhancement of light output at narrow angles and provided strategies to minimize luminance fluctuations at such angles, contributing to the development of high‐precision luminance control in AMOLED displays. [ABSTRACT FROM AUTHOR]

Photoacoustic waves can be detected by recording optical beam deflection as a result of density gradients inherent in the waves. Beam deflection can be recorded from a single laser beam placed at a distance from the source where data are generated as a function of time, or by recording beam deflections at a single time as the position of the probe beam is varied. For either case, the deflection signal is shown to be described by an Abel transform of the pressure gradient. Here, the inversion of beam deflection data from photoacoustic sources with symmetry in one, two, and three dimensions is investigated. An iterative method based on total variation regularization and a regression procedure based on Lasso regularization are shown to result in accurate reproductions of the theoretical expressions that describe photoacoustic waves from simple sources. [ABSTRACT FROM AUTHOR]

In this study, we focus on a static spherically symmetric f(R) black hole spacetime characterized by a linear dark matter-related parameter. Our investigation delves into understanding the influence of different assumed values of this parameter on the observable characteristics of the black hole. To fulfill this task, we investigate the light deflection angles, which are inferred from direct analytical calculations of null geodesics. To examine the black hole's properties further, we assume an optically thin accretion disk and explore various emission profiles. Additionally, we investigate the shadow cast by the illuminated black hole when affected by the disk. Furthermore, we simulate the brightness of an infalling spherical accretion in the context of silhouette imaging for the black hole. Our findings indicate that, except for some specific cases, the observed brightness of the accretion disk predominantly arises from direct emission, rather than lensing and photon rings. Moreover, we reveal that the linear dark parameter of the black hole significantly influences the shadow size and brightness. Our discussion covers both analytical and numerical approaches, and we utilize ray-tracing methods to produce accurate visualizations. [ABSTRACT FROM AUTHOR]

The optical characteristics of three types of black holes (BHs) surrounded by a thin accretion disk are discussed, namely the Schwarzschild BH, Bardeen BH, and Hayward BH. We calculate the deflection angle of light as it traverses the vicinity of each BH using numerical integration and semi-analytical methods, revealing that both approaches can effectively elucidate the deflection of light around the BH. We investigate the optical appearance of the accretion disk and its corresponding observational images at various viewing angles, discovering that the luminosity in the region near the BH on the inner side of the accretion disk is higher than that on the outer side owing to higher material density in closer proximity to the BH. We observe a significant accumulation of brightness on the left side of the accretion disk, attributed to the motion of matter and geometric effects. Our findings emphasize the significant influence of the observation inclination angle on the observed outcomes. An increase in the observation inclination angle results in the separation of higher-order images. With the improvement in EHT observation accuracy, we believe that the feature of a minimal distance between the innermost region of the direct image of the Hayward BH and the outermost region of the secondary image can be used as an indicator for identifying Hayward BHs. [ABSTRACT FROM AUTHOR]

Inspired by M-theory scenarios, we investigate optical properties of black holes in the Starobinsky–Bel–Robinsion gravity. Precisely, we study the shadows and the deflection angle of light rays by this class of black holes in such a novel gravity. First, we approach the shadows of the Schwarzschild-type solutions. As expected, we find perfect circular shadows where the size decreases with a stringy gravity parameter denoted by β . We reveal that this parameter is constrained by the shadow existence. Combining the Newman–Janis algorithm and the Hamilton–Jacobi mechanism, we examine the shadow behaviors of the rotating solutions in terms of one-dimensional real curves. Precisely, we obtain various sizes and shapes depending on the rotating parameter and the stringy gravity parameter a and β , respectively. To examine the shadow geometric deformations, we study the astronomical observables and the energy emission rate. As envisaged, we show that a and β have an impact on such shadow behaviors. For specific values of a, we remark that the obtained shadow shapes share certain similarities with the ones of the Kerr black holes in the plasma backgrounds. Using the Event Horizon Telescope observational data, we provide predictions for the stringy gravity parameter β which could play a relevant role in the M-theory compactifications. After that, we discuss the behaviors of the light rays near to such four dimensional black holes by calculating the deflection angle in terms of a required moduli space. [ABSTRACT FROM AUTHOR]

This review provides an overview of the major, currently used techniques for investigating the Soret effect and measuring thermodiffusion and Soret coefficients, and in most cases also isothermal Fickian diffusion coefficients, in liquid mixtures. The methods are introduced with a focus on binary mixtures. The optical methods comprise optical beam deflection (OBD), optical digital interferometry (ODI) both on the ground and under microgravity conditions in the SODI-IVIDIL experiment for the study of the influence of vibrations onboard the International Space Station, which are all based on Soret cells. The transient holographic grating technique of thermal diffusion-forced Rayleigh scattering (TDFRS) employs light not only for detection of the concentration changes but also for optical volume heating. Thermogravitational columns (TGC) utilize the coupling between convection and thermodiffusion to create concentration changes inside a vertical column with a horizontal temperature gradient. While samples are analyzed after extraction from the column in a classical setup, the recently developed transparent microcolumn allows for interferometric in situ monitoring of the concentration field. The most recent technique relies on the measurement of giant non-equilibrium fluctuations (NEFs) by small-angle light scattering techniques. Research on ternary mixtures, both on the ground and in microgravity, has gained momentum in the context of the DCMIX microgravity project of ESA. Most techniques employed for binaries can be extended to ternaries by introducing a second detection color or by analyzing both refractive index and density of extracted TGC samples. The accuracy is limited by the unavoidable inversion of the so-called contrast factor matrix. [ABSTRACT FROM AUTHOR]

In this paper, the deflection angle of light by traversable wormholes, which are supported by the three‐form fields, are studied. The specific forms of the redshift and shape functions that produce results compatible with the energy conditions at throat of the wormholes are used. Having used the well‐defined parameter sets of the three‐form wormholes, the photon geodesic motion is investigated under the effective potential of the wormhole background. As a result, it is discovered that the radius of the photon sphere can be used to analyze the geometrical structures of a physical wormhole. The analytical form of the effective potential is used to figure out a deflection angle of light caused by wormholes with the three‐from fields. In this work, the relativistic images generated from the wormholes are also constructed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate a solution for an asymptotic, magnetically-charged, non-singular (AMCNS) black hole. By utilizing the Gauss–Bonnet theorems, we aim to unravel the intricate astrophysics associated with this unique black hole. The study explored various aspects including the black hole's gravitational field, intrinsic properties, light bending, the shadow and greybody bounding of the black hole. Through rigorous calculations and simulations, we derive the weak deflection angle of the optical metric of AMCNS black hole. Additionally, we investigate the impact of the dark matter medium on the deflection angle, examined the distinctive features of the black hole's shadow, and bound its greybody factors. Our findings not only deepen our understanding of gravitational lensing but also pave the way for future improvements in black hole theories by minimizing restrictive assumptions and incorporating a more realistic representation of these cosmic phenomena. [ABSTRACT FROM AUTHOR]

The optical properties of rotating black holes in Kaluza–Klein theory described by the total mass, spin, and electric and magnetic charges are investigated in detail. Using a developed general relativistic ray-tracing code to calculate the motion of photons, shadows of Kaluza–Klein black holes are generated. The properties of the shadow and the light deflection angle around these black holes are also studied in order to put constraints on the parameters of Kaluza–Klein black holes using M87* shadow observations. The possibility of imposing constraints on Kaluza–Klein black holes using shadow observations is investigated. Moreover, we find that small charges (electric and magnetic) of the black hole can meet these constraints. We conclude that with the current precision of the M87* black hole shadow image observation by the EHT collaboration, the shadow observations of Kaluza–Klein black holes are indistinguishable from that of the Kerr black hole. Much better observational accuracy than the current capabilities of the EHT collaboration are required in order to place verified constraints on the parameters of modified theories of gravity in the strong field regime. [ABSTRACT FROM AUTHOR]

The astrophysical consequences of the presence of a quintessence scalar field on the evolution of the horizon and on the accretion disk surrounding a static black hole, in the scalar–vector–tensor version of modified gravity (MOG), are investigated. The positions of the stable circular orbits of the massive test particles, moving around the central object, are obtained from the extremum of the effective potential. Detailed calculations are also presented to investigate the light deflection, shadow and Shapiro effect for such a black hole. The electromagnetic properties of the accretion disks that form around such black holes are considered in detail. The energy flux and efficiency parameter are estimated analytically and numerically. A comparison with the disk properties in Schwarzschild geometry is also performed. The quantum properties of the black hole are also considered, and the Hawking temperature and the mass loss rate due to the Hawking radiation are considered. The obtained results may lead to the possibility of direct astrophysical tests of black hole type objects in modified gravity theories. [ABSTRACT FROM AUTHOR]

Photoacoustic microscopy with high spatial resolution and fast imaging acquisition allows observing dynamic processes of optical absorption-based microanatomic structures in three dimensions. An evanescent sensor accesses ultrasonic detection with high sensitivity and broad bandwidth while suffering from limited field of view (FOV), thus compromising the photoacoustic imaging acquisition rate. Here, we develop an optical-scanning evanescent sensor by fast deflection of the interrogation light along the interface of prism and water using a one-dimensional galvanometer, demonstrating excellent detection sensitivity of ∼132 Pa with a broadband frequency response of >140-MHz at an enlarged FOV of ∼2.90 × 0.19 mm2. Incorporating the optical-scanning evanescent sensor in photoacoustic microscopy, a volumetric image (∼3.0 × 0.25 × 1.0 mm3) with micrometer-scale spatial resolution is acquired within ∼2.5 s by synergistically scanning both photoacoustic illumination laser and sensor's interrogation light. High-speed imaging of flowing microparticles within a capillary tube offers the visualizations of the traveling processes in three dimensions. Potentially, the optical-scanning evanescent sensor allows photoacoustic microscopy accommodating to dynamic imaging at cellular level such as in vivo flow cytometry of circulating tumor cells. [ABSTRACT FROM AUTHOR]

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To visualize what is seen by an observer in curved spacetime, both general relativistic effects and special relativistic effects need to be considered. In this study, the author analytically proved that the zenith view seen by an observer falling freely into a Schwarzschild black hole (that is, the observer's view of the point on the opposite side of the black hole) becomes enlarged, "redder," and darker as the observer falls from an arbitrary initial rest position. An equation expressing the magnification factor of the zenith view was also derived. The derived factor characterizes the brightness and frequency of light emanated from the zenith view. Using these results, the author derived visualizations of the zenith views for various scenarios. As expressed by the derivations presented here, the moment when the observer sees the zenith view appear twice as large compared to the initial rest position coincides with the crossing of the event horizon; that is, a freely falling observer can detect the horizon through the simple procedure of continuing to observe the zenith view. This result implies that the effect of aberration dominates the effect of light deflection while the observer is falling. [ABSTRACT FROM AUTHOR]

Little is known why illumination of linearly polarized continuous‐wave laser light can induce gyrotropy (optical rotatory power) and macroscopic circular/screwing deformations in amorphous As2S3. Gyrotropy appears through scattering and deflection of the incident light in combination with negative photoinduced birefringence. The gyrotropy could also trigger atomic motions under photoinduced fluidity, which produces macroscopic deformations. [ABSTRACT FROM AUTHOR]

The optical properties of a thin-shell wormhole (TSW) with a Hayward profile is investigated. Adopting the ray-tracing method, we demonstrate that the TSW's contralateral spacetime is capable of reflecting a significant portion of light back to the observer spacetime. We analyze the effective potential, light deflection, and azimuthal angle of the TSW and find that these quantities are affected by the mass ratio of the black holes (BHs). Specifically, if the mass of the contralateral spacetime BH is greater than that of the original spacetime BH, and the impact parameter satisfies the condition H b c2 < b 1 < b c1 , the trajectory of the photon exhibits round-trip characteristics. Assuming the presence of a thin accretion disk surrounding the observing spacetime BH, our results indicate that the image formed by the TSW exhibits additional photon rings and a lensing band compared to an image produced by a BH alone. [ABSTRACT FROM AUTHOR]

Little is known why illumination of linearly polarized continuous‐wave laser light can induce gyrotropy (optical rotatory power) and macroscopic circular/screwing deformations in amorphous As2S3. Gyrotropy appears through scattering and deflection of the incident light in combination with negative photoinduced birefringence. The gyrotropy could also trigger atomic motions under photoinduced fluidity, which produces macroscopic deformations. [ABSTRACT FROM AUTHOR]

We propose a theoretical method for enantio-discrimination based on the light deflection effect in four-level models of chiral molecules. This four-level model consists of a cyclic three-level subsystem coupled by three strong driving fields and an auxiliary level connected to the cyclic three-level subsystem by a weak probe field. It is shown that the induced refractive index for the weak probe field is chirality-dependent. Thus, it will lead to chirality-dependent light deflection when the intensities of two of the three strong driving fields are spatially inhomogeneous. As a result, the deflection angle of the weak probe light can be utilized to detect the chirality of pure enantiomers and enantiomeric excess of the chiral mixture. Therefore, our method may act as a tool for enantio-discrimination. [ABSTRACT FROM AUTHOR]

Launch of the Gaia space observatory started a new era in astrometry when the accuracy of star coordinates increased by thousands of times. Significant improvement in accuracy was also expected for the coordinates of the Solar system bodies. Gaia Data Release 3 (DR3) provided us with the data that could be used to test our expectations. In this work, we refine the orbits of a number of outer planetary satellites using both ground-based and Gaia observations. From 13 outer satellites observed by Gaia , we chose 6 to obtain their orbits. Some specific moments in using observations of outer satellites made by Gaia are demonstrated. These peculiarities stem from scanning motion of Gaia , in particular from the fact that the accuracy of observations is significantly different along and across the scanning direction. As expected, Gaia observations proved to be more precise than those made from Earth, which results in more accurate satellite ephemerides. We estimate accuracy of the ephemerides of considered satellites for the interval between 1996 and 2030. As astrometric positions published in Gaia DR3 were not corrected for the relativistic light deflection by the Sun, we took into account this effect, which slightly diminished the rms residuals. In addition, relativistic light deflection by the giant planets was estimated, which, as it turned out, can be neglected with the given accuracy of Gaia observations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Goniometric methods of measuring the refractive index of optically transparent materials based on the refraction of light by a triangular prism are studied. A modified minimum deviation method and 3 modified constant deviation methods are examined which make it possible to determine the refractive indices of triangular prisms with unknown refracting angles. According to the modified prism methods the deflection angles of the light by the prism are measured with a goniometer, while the refractive index of the material and the refraction angles of the prism are determined by solving systems of equations. Thus, there is no need for preliminary measurement of the prism angles, which would require special autocollimation goniometers. In addition, in the modified prism methods, light reflected from the faces of the prism is not used, which makes it possible to extend the spectral range of a measurement of the refractive index to the infrared and ultraviolet ranges. The errors in measurements of the refractive index by these methods are compared for the example of a prism with a refractive index of 1.5 and a refraction angle of 60°. It is shown that the modified minimum deviation method has the smallest error among all the prism methods, so it can be recommended for high-precision measurements of the refractive index in those cases where the refractive angles of the prism are unknown or it is technically difficult to measure them. The modified methods examined here can be used for measuring the refractive index of triangular prisms made of optically transparent materials, as well as of liquids poured into hollow prisms with plane-parallel transparent windows. Practical implementation of methods of this type should be useful in the optical, chemical, and food industries for monitoring the composition and properties of optically transparent materials. [ABSTRACT FROM AUTHOR]

The present paper is devoted to analyzing light deflection caused by the presence of a cosmological constant in a space-time described by the Szekeres–Szafron metric. We use the orbital equation for light to calculate the deflection angle in gravitational lensing in the equatorial plane of the Szekeres–Szafron metric. The present study confirms that the cosmological constant has an effect on gravitational lensing. [ABSTRACT FROM AUTHOR]

Epsilon-near-zero nanoantennas can be used to tune the far-field radiation pattern due to their exceptionally large intensity-dependent refractive index. In this study, we propose a hybrid optical antenna based on indium tin oxide (ITO) to enable optical tuning of the deflection of radiation, specifically a hybrid structure antenna of ITO and dielectric material, which makes the deflection angle changes 17 ∘ as incident intensities increase. Moreover, by employing an array of ITO or hybrid nanodisks, we can enhance the unidirectionality of the radiation pattern, resulting in a needle-like shape with an angular beam width α < 8 ∘ of the main lobe. The deflection angle of the radiation pattern response with the needle-like lobe paves the way for further studies and applications in beam steering and optical modulation where dynamic control of the nanoantennas is highly desirable. [ABSTRACT FROM AUTHOR]

Pulsed laser ablation in liquid (PLAL) has gained popularity over time as an efficient method for fabrication of nanoparticles (NPs). This method depends on laser-induced dynamics at the solid–liquid interface, which is influenced by the experimental parameters. Hence, it becomes necessary to study the effect of various parameters for efficient synthesis of NPs and better control over their properties. The present study elucidates the role of liquid ambient in determining the properties of NPs. The effect of viscosity on the size of NPs is studied by conducting experiments in three liquids, viz., Distilled water (DW), propylene glycol (PG), and glycerol (GOL). This study uncovers that size of NPs significantly depends on the viscosity of liquid. The size of NPs is measured to be 35, 52, and 65 nm for DW, PG, and GOL, respectively. The dynamical processes of PLAL were probed using optical beam deflection technique with an attempt to connect the NPs size distribution to the bubble size in respective liquid. Maximum cavitation bubble radius was estimated to be 2.02, 1.85, and 1.45 mm for DW, PG, and GOL, respectively. Laser-produced craters were studied to know their effect on surface morphology. Theoretical calculation of the binding energies of PG and GOL complement the experimental results. This series of studies performed in the present work will further enhance the control over NPs during PLAL. [ABSTRACT FROM AUTHOR]

Setup-related aspects of background-oriented schlieren (BOS) experiments are discussed focusing on a sensitivity parameter S, which represents the relation between light deflection and resulting BOS signal, and the geometric blur. An analytic expression for the geometric blur by means of the circle of confusion (CoC) was derived which shows a proportional relation to the sensitivity factor S. The theoretical findings were validated in a reference experiment using generic distortions in glass plates. It was found that the filtering effect of the blur decreases the maximum background shift and its influence can be expressed with a blur loss factor B, which depends on the size of the CoC in relation to the investigated object. Multiplying the setup sensitivity S with the blur loss B results in the effective sensitivity S eff that determines the maximum achievable BOS signal of a schlieren object. For the investigated reference objects, the maximum effective sensitivity S eff was found to occur at CoC sizes in the object domain from 2.5 to 3.8 times the extent of the investigated objects. A step-by-step method is proposed for designing BOS experiments to obtain a maximum signal strength. The design parameters are further discussed specifically in regard to rotor tip vortex visualization, for which a variety of previously reported experiments are compared. A simple prediction method for the BOS signal of blade tip vortices is proposed and validated with experimental data from a rotor test stand. The application of the method to rotor systems of different size shows the requirement for increasingly higher sensitivity values for visualizing vortices of small-scale rotors. [ABSTRACT FROM AUTHOR]

The effect of spacetime curvature on optical properties may provide an opportunity to suggest new tests for gravity theories. In this paper, we investigated gravitational weak lensing around a Bardeen black hole with the string clouds parameter. First, we examined the horizon structure in the presence of string clouds around the gravitational compact object defined by Bardeen spacetime. The effect of gravitational weak lensing in a plasma medium is also discussed. According to the findings, the influence of the string cloud parameter on the circular orbits of a light ray around the black hole is greater than that in the Schwarzschild case, while the influence of the charge is reversed. The deflection angle of light rays in weak lensing is also used to study how much the image is magnified. [ABSTRACT FROM AUTHOR]

Galactic microlensing has been widely used to study stars and planets. The stellar wind plays an important role in the formation, environment, and habitability of the planet. In this work, we study a binary microlensing system including the stellar wind, i.e. a star with a plasma environment plus a planet. Plasma surrounding the main lens causes chromatic deflection of the light rays, in addition to the gravitational one. As a result, such a lensing system can generate complicated caustics that depend on the different lensing parameters. In this work, we study the magnification curves for different traces of the background source and compare the transitions of the formation of 'hill and hole' in the magnification curves. We find that the plasma will cause extra caustic, shrink the central caustics generated by the star, and push the caustic by the planet outwards. Observations and modelling of binary microlensing curves with taking plasma effect into account can provide a potential method to study the plasma environment of the stars. In case of a high plasma density of the stellar wind, the plasma lensing effects will be observable in the sub-mm band. [ABSTRACT FROM AUTHOR]

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