Journal articles: 'Wavefront'

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Drew, Patrick J., and Daniel E. Feldman. "Representation of Moving Wavefronts of Whisker Deflection in Rat Somatosensory Cortex." Journal of Neurophysiology 98, no. 3 (September 2007): 1566–80. http://dx.doi.org/10.1152/jn.00056.2007.

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Rats rhythmically sweep their whiskers over object features, generating sequential deflections of whisker arcs. Such moving wavefronts of whisker deflection are likely to be fundamental elements of natural somatosensory input. To determine how moving wavefronts are represented in somatosensory cortex (S1), we measured single- and multiunit neural responses in S1 of anesthetized rats to moving wavefronts applied through a piezoelectric whisker deflector array. Wavefronts consisted of sequential deflections of individual whisker arcs, which moved progressively across the whisker array. Starting position (starting arc), direction, and velocity of wavefronts were varied. Neurons responded strongly only when wavefront starting position included their principal whisker (PW). When wavefronts started at neighboring positions and swept through the PW, responses to the PW arc were suppressed by ≤95%, and responses over the entire wavefront duration were suppressed by ≤60% compared with wavefronts that initiated with the PW. Suppression occurred with interarc deflection delays of ≥5 ms, was maximal at 20 ms, and recovered within 100–200 ms. Suppression of PW arc responses during wavefronts was largely independent of wavefront direction. However, layer 2/3 neurons showed direction selectivity for responses to the entire wavefront (the entire sequence of SW and PW arc deflection). Wavefront direction selectivity was correlated with receptive field somatotopy and reflected differential responses to the specific SWs that were deflected first in a wavefront. These results indicate that suppressive interwhisker interactions shape responses to wavefronts, resulting in increased salience of wavefront starting position, and, in some neurons, preference for wavefront direction.

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Qiu, Xuejing, Tao Cheng, Lingxi Kong, Shuai Wang, and Bing Xu. "A Single Far-Field Deep Learning Adaptive Optics System Based on Four-Quadrant Discrete Phase Modulation." Sensors 20, no. 18 (September 8, 2020): 5106. http://dx.doi.org/10.3390/s20185106.

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In adaptive optics (AO), multiple different incident wavefronts correspond to a same far-field intensity distribution, which leads to a many-to-one mapping. To solve this problem, a single far-field deep learning adaptive optics system based on four-quadrant discrete phase modulation (FQDPM) is proposed. Our method performs FQDPM on an incident wavefront to overcome this many-to-one mapping, then convolutional neural network (CNN) is used to directly predict the wavefront. Numerical simulations indicate that the proposed method can achieve precise high-speed wavefront correction with a single far-field intensity distribution: it takes nearly 0.6ms to complete wavefront correction while the mean root mean square (RMS) of residual wavefronts is 6.3% of that of incident wavefronts, and the Strehl ratio of the far-field intensity distribution increases by 5.7 times after correction. In addition, the experiment results show that mean RMS of residual wavefronts is 6.5% of that of incident wavefronts and it takes nearly 0.5 ms to finish wavefront reconstruction, which verifies the correctness of our proposed method.

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Zhao, Mengmeng, Wang Zhao, Kangjian Yang, Shuai Wang, Ping Yang, Fengjiao Zeng, Lingxi Kong, and Chao Yang. "Shack–Hartmann Wavefront Sensing Based on Four-Quadrant Binary Phase Modulation." Photonics 9, no. 8 (August 16, 2022): 575. http://dx.doi.org/10.3390/photonics9080575.

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Aiming at the problem that it is difficult for the conventional Shack–Hartmann wavefront sensor to achieve high-precision wavefront reconstruction with low spatial sampling, a kind of Shack–Hartmann wavefront sensing technology based on four-quadrant binary phase modulation is proposed in this paper. By introducing four-quadrant binary phase modulation into each subaperture, the technology is able to use an optimization algorithm to reconstruct wavefronts with high precision. The feasibility and effectiveness of this method are verified at extreme low spatial frequency by a series of numerical simulations, which show that the proposed method can reliably reconstruct wavefronts with high accuracy with rather low spatial sampling. In addition, the experiment demonstrates that with a 2 × 2 microlens array, the four-quadrant binary phase-modulated Shack–Hartmann wavefront sensor is able to achieve approximately 54% reduction in wavefront reconstitution error over the conventional Shack–Hartmann wavefront sensor.

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PRASAD, PHOOLAN, and K. SANGEETA. "Numerical simulation of converging nonlinear wavefronts." Journal of Fluid Mechanics 385 (April 25, 1999): 1–20. http://dx.doi.org/10.1017/s0022112098003310.

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The propagation of a two-dimensional weakly nonlinear wavefront into a polytropic gas in a uniform state and at rest has been studied. Successive positions of the wavefront and the distribution of amplitude on it are obtained by solving a system of conservation forms of the equations of weakly nonlinear ray theory (WNLRT) using a TVB scheme based on the Lax–Friedrichs flux. The predictions of the WNLRT are found to be qualitatively quite different from the predictions of the linear theory. The linear wavefronts leading to the formation of caustics are replaced by nonlinear wavefronts with kinks. By varying the initial shape of the wavefront and the amplitude distribution on it, the formation and separation of kinks on the wavefront has been studied.

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Zabotin, Nikolay A., Oleg A. Godin, Paul C. Sava, and Liudmila Y. Zabotina. "Tracing Three-Dimensional Acoustic Wavefronts in Inhomogeneous, Moving Media." Journal of Computational Acoustics 22, no. 02 (April 17, 2014): 1450002. http://dx.doi.org/10.1142/s0218396x14500027.

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We present a numerical implementation of an alternative formulation of the geometrical, or ray, acoustics, where wavefronts rather than rays are the primary objects. Rays are recovered as a by-product of wavefront tracing. The alternative formulation of the geometrical acoustics is motivated, first, by the observation that wavefronts are often more stable than rays at long-range sound propagation, and, second, by a need for computationally efficient modeling of high-frequency acoustic fields in three-dimensionally inhomogeneous, moving or motionless fluids. Wavefronts are found as a finite-difference solution to a system of partial differential equations, which is equivalent to the eikonal equation and is a direct implementation of the intuitive Huygens' wavefront construction. The finite-difference algorithm is an extension of the approach originally developed in the framework of an open source Madagascar project. Benchmark problems, which admit exact, analytic solutions of the eikonal equation, are formulated and utilized to verify the finite-difference wavefront tracing algorithm. Huygens' wavefront tracing (HWT) is applied to modeling sound propagation in three-dimensionally inhomogeneous ocean and atmosphere.

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Malek, Stephanie C., Adam C. Overvig, Sajan Shrestha, and Nanfang Yu. "Active nonlocal metasurfaces." Nanophotonics 10, no. 1 (September 24, 2020): 655–65. http://dx.doi.org/10.1515/nanoph-2020-0375.

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AbstractActively tunable and reconfigurable wavefront shaping by optical metasurfaces poses a significant technical challenge often requiring unconventional materials engineering and nanofabrication. Most wavefront-shaping metasurfaces can be considered “local” in that their operation depends on the responses of individual meta-units. In contrast, “nonlocal” metasurfaces function based on the modes supported by many adjacent meta-units, resulting in sharp spectral features but typically no spatial control of the outgoing wavefront. Recently, nonlocal metasurfaces based on quasi-bound states in the continuum have been shown to produce designer wavefronts only across the narrow bandwidth of the supported Fano resonance. Here, we leverage the enhanced light-matter interactions associated with sharp Fano resonances to explore the active modulation of optical spectra and wavefronts by refractive-index tuning and mechanical stretching. We experimentally demonstrate proof-of-principle thermo-optically tuned nonlocal metasurfaces made of silicon and numerically demonstrate nonlocal metasurfaces that thermo-optically switch between distinct wavefront shapes. This meta-optics platform for thermally reconfigurable wavefront shaping requires neither unusual materials and fabrication nor active control of individual meta-units.

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Lee, Beom-Ryeol, José Gil Marichal-Hernández, José Manuel Rodríguez-Ramos, Wook-Ho Son, Sunghee Hong, and Jung-Young Son. "Wavefront Characteristics of a Digital Holographic Optical Element." Micromachines 14, no. 6 (June 10, 2023): 1229. http://dx.doi.org/10.3390/mi14061229.

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In this study, a 50 × 50 mm holographic optical element (HOE) with the property of a spherical mirror was recorded digitally on a silver halide photoplate using a wavefront printing method. It consisted of 51 × 96 hologram spots with each spot measuring 0.98 × 0.52 mm. The wavefronts and optical performance of the HOE were compared with those of reconstructed images from a point hologram displayed on DMDs of different pixel structures. The same comparison was also performed with an analog-type HOE for a heads-up display and with a spherical mirror. A Shack–Hartmann wavefront sensor was used to measure the wavefronts of the diffracted beams from the digital HOE and the holograms as well as the reflected beam from the analog HOE and the mirror when a collimated beam was incident on them. These comparisons revealed that the digital HOE could perform as a spherical mirror, but they also revealed astigmatism—as in the reconstructed images from the holograms on DMDs—and that its focusability was worse than that of the analog HOE and the spherical mirror. A phase map, i.e., the polar coordinate-type presentation of the wavefront, could visualize the wavefront distortions more clearly than the reconstructed wavefronts obtained using Zernike polynomials. The phase map revealed that the wavefront of the digital HOE was more distorted than those of the analog HOE and the spherical mirror.

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Faria-Ribeiro, Miguel, José Manuel González-Méijome, Maria Isabel Pinho Ferreira, Anabela Ferreira Morais-Borges, and José Salgado-Borges. "Analysis of Wavefront Data Obtained With a Pyramidal Sensor in Pseudophakic Eyes Implanted With Diffractive Intraocular Lenses." Journal of Refractive Surgery 39, no. 7 (July 2023): 438–44. http://dx.doi.org/10.3928/1081597x-20230523-01.

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Purpose: To investigate the clinical validity of using wavefront measurements obtained with a recently available pyramidal aberrometer to assess the optical quality of eyes implanted with diffractive intraocular lenses (IOLs). Methods: Individual biometric data were used to create models of pseudophakic eyes implanted with two diffractive IOLs. Their synthetic wavefronts were calculated by ray-tracing with near infrared wavelength (0.85 μm). Comparisons of the through-focus visual acuity of 12 pseudophakic eyes were obtained with three different methods: clinical defocus curves; simulated defocus curves calculated from ray-tracing in the customized model eyes; and through-focus simulated defocus curves calculated from the wavefront data measured with a pyramidal aberrometer. Results: Image quality calculated from wavefront data obtained by ray-tracing with 0.85 μm wavelength, without scaling the phase to 0.55 μm, resulted in a significantly different through-focus curve compared to the reference values. Even so, after scaling of the wavefront data to 0.55 μm, the defocus curves calculated from the wavefronts measured with the pyramidal aberrometer did not match the shape and the depth of field of the clinical defocus curves or the theoretical expected values. Conclusions: Correcting for the longitudinal chromatic aberration of the eye when measuring the wavefront of eyes implanted with diffractive IOLs under near infrared light only accounts for the best focus shift due to the longitudinal chromatic aberration, but not for the wavelength dependence of the diffractive element. The pyramidal sensor does not seem to properly sample the slopes of a wavefront measured from a pseudophakic eye implanted with a presbyopia-correcting diffractive IOL to a clinically acceptable level. [ J Refract Surg . 2023;39(7):438–444.]

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Deng, Yangchun, Junlei Zhao, Yun Dai, and Yudong Zhang. "Simultaneous quantification of longitudinal and transverse ocular chromatic aberrations with Hartmann–Shack wavefront sensor." Journal of Innovative Optical Health Sciences 11, no. 04 (July 2018): 1850021. http://dx.doi.org/10.1142/s1793545818500219.

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A simple method to objectively and simultaneously measure eye’s longitudinal and transverse chromatic aberrations was proposed. A dual-wavelength wavefront measurement system using two Hartmann–Shack wavefront sensors was developed. The wavefronts of the red (639.1[Formula: see text]nm) and near-infrared (786.0[Formula: see text]nm) lights were measured simultaneously for different positions in the model eye. The chromatic wavefronts were converted into Zernike polynomials. The Zernike tilt coefficient (first term) was used to calculate the transverse chromatic aberration along the [Formula: see text]-direction, while the Zernike defocus coefficient (fourth term) was used to calculate the longitudinal chromatic aberration. The measurement and simulation data were consistent.

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Meng, Yunlong, Xinyu Shen, Junyang Xie, Yao Peng, Xiaowen Shao, Feng Yan, and Cheng Yang. "One-Dimensional High-Resolution Wavefront Sensor Enabled by Subwavelength Compound Gratings." Photonics 10, no. 4 (April 7, 2023): 420. http://dx.doi.org/10.3390/photonics10040420.

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Angle sensors are widely used for wavefront measurements, which is attributed to their integration and robustness. Currently, commercial sensors are available with pixel sizes in the order of wavelengths. However, the spatial resolution of angle sensors still lags far behind. Here, we report a one-dimensional, high-resolution wavefront sensor. It was produced by introducing subwavelength compound gratings above the pixels. The gratings involved could be replaced by the sensor’s intrinsic readout circuitry without additional operation. The experimental results showed that it had a spatial resolution of 1.4 µm, two orders of magnitude higher than that of the Shack–Hartmann wavefront sensor. The significant increase in spatial resolution enables angle sensors to reconstruct complex wavefronts accurately.

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Zhang, Guang Bin, Hong Chun Shu, and Ji Lai Yu. "An Approach of Wavefront Identification for Traveling Wave Fault Location Based on Harris Corner Detector." Advanced Materials Research 960-961 (June 2014): 1100–1103. http://dx.doi.org/10.4028/www.scientific.net/amr.960-961.1100.

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Wavefront identification is important for traveling based fault location. In order to improve its reliability, a novel wavefront identification method based on Harris corner detector has been proposed in this paper. The principle of single-ended traveling wave fault location was briefly introduced at first, and the features of wavefronts generated by faults on transmission lines were analyzed. The arrival of traveling waves' wavefronts is considered as corner points in digital image of waveshape. The corner points can be extracted precisely by Harris corner detector, and both false corner points and non-fault caused disturbance can be eliminated according to the calculated distance between two neighbour corner points and the angle of the corner point. The proposed method is proved feasible and effective by digital simulated test.

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Coultrip, Robert L. "High-accuracy wavefront tracing traveltime calculation." GEOPHYSICS 58, no. 2 (February 1, 1993): 284–92. http://dx.doi.org/10.1190/1.58020284.1.

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Conventional ray-tracing algorithms for first-arrival calculation suffer from drawbacks such as (1) no guarantee of finding the globally minimum traveltime path when multiple paths exist, (2) shadow zones, and (3) trouble finding minimum traveltime paths containing refraction and/or diffraction energy. Algorithms that trace wavefronts circumvent these problems. The new wavefront-tracing algorithm presented here is based on an earth model consisting of uniform-velocity triangular cells with nodes placed at vertices and along cell edges. Nodes are places where traces of first arrival wavefronts (propagation directions and arrival times) are stored. The algorithm works by propagating wavefronts (sampled at the nodes) away from the source throughout the entire model. Wavefronts are propagated locally as diffraction, direct arrival, or critically refracted energy that implicitly describe minimum time paths. Once the first arrival wavefront is sampled throughout the model, traveltimes and raypaths from the source to receivers are easily calculated. This algorithm computes the globally minimum time paths from the source to all points in the model regardless of model complexity and the number of locally minimum traveltime paths. Traveltime calculations are highly accurate and computation time is O(n log2 n) for n nodes. Use of triangular cells allows for cell boundaries that follow, say, fault planes and dipping beds, without resorting to stair-step approximations inherent with rectangular cells. This method can be extended to three dimensional (3-D) problems.

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Tseluiko, D., N. S. Alharthi, R. Barros, and K. R. Khusnutdinova. "Internal ring waves in a three-layer fluid on a current with a constant vertical shear." Nonlinearity 36, no. 6 (May 18, 2023): 3431–66. http://dx.doi.org/10.1088/1361-6544/accfe0.

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Abstract Oceanic internal waves often have curvilinear fronts and propagate over vertically sheared currents. We present the first study of long weakly-nonlinear internal ring waves in a three-layer fluid in the presence of a horizontally uniform background current with a constant vertical shear. The leading order of this theory leads to the angular adjustment equation—a nonlinear first-order ordinary differential equation describing the dependence of the linear long-wave speed on its angle to the direction of the current. The compact ring waves, well studied in the absence of a current, correspond to the singular solution (envelope of the general solution) of this equation, and they can exist only under certain conditions. The constructed solutions reveal qualitative differences in the shapes of the wavefronts of the two baroclinic modes: the wavefront of the faster mode is elongated in the direction of the current, while the wavefront of the slower mode is squeezed. Moreover, depending on the vorticity strength, several different regimes have been identified. When the vertical shear is weak, part of the wavefront is able to propagate upstream, while when the shear is strong enough, the whole wavefront propagates downstream. A richer pattern of behaviour is observed for the slower mode. As the shear increases, singularities of the swallowtail-type may arise and, eventually, solutions with compact wavefronts crossing the downstream axis cease to exist. We show that the latter is related to the long-wave instability of the base flow. We obtain the cKdV-type amplitude equation and examine analytical expressions for its coefficients. Using this cKdV-type equation we numerically model the evolution of the waves for both modes. The initial stage of the evolution is in agreement with the leading-order predictions for the deformations of the wavefronts. Then, as the wavefronts expand, strong dispersive effects occur in the upstream direction. Moreover, when nonlinearity is enhanced, fission of waves is observed in the upstream part of the ring waves.

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Zhao, Mengshi, Tao Li, Qi Yin, Shijie Fu, and Wei Wei. "Formation and propagation characteristics of pseudo-wavefronts of optical polarization states signal inside OPGW under lightning strikes." Journal of Physics: Conference Series 2741, no. 1 (April 1, 2024): 012001. http://dx.doi.org/10.1088/1742-6596/2741/1/012001.

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Abstract Lightning strikes on Optical Fiber Composite Overhead Ground Wires (OPGW) result in a phenomenon where the current traveling wave along the OPGW’s outer stranding propagates faster than the optical signals inside the fiber. This leads to the emergence of pseudo-wavefronts ahead of the optical polarization state signal after lightning strikes OPGW, introducing errors in lightning point localization based on the optical polarization state. This paper investigates the formation and propagation characteristics of pseudo-wavefronts. The study employs theoretical analysis and simulation to examine the process of optical polarization state formation during OPGW lightning strikes. Additionally, it conducts comparative analyses between laboratory-simulated OPGW lightning strikes and field measurements obtained from OPGW lightning monitoring systems. The results affirm the existence of the proposed pseudo-wavefront phenomenon, which substantially impacts the precision of lightning point localization. Notably, the duration of pseudo-wavefront effects increases with greater distance from the lightning point and higher lightning current amplitudes. These findings raise questions regarding the suitability of traditional wavefront calibration methods based on the traveling wave approach. This research contributes valuable insights for the practical implementation of lightning point localization methodologies relying on OPGW self-sensing technology.

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Williams, Jeremiah. "Spatial Evolution of the Dust-Acoustic Wave." Plasma Science, IEEE Transactions on 41, no. 4 (April 2013): 788–93. http://dx.doi.org/10.1109/tps.2012.2231083.

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Over the past twenty years, the dust-acoustic wave (DAW) has been a subject of intense study. In this paper, high-speed video imaging is employed to measure the evolution of wavefronts of a propagating DAW as it propagates through a weakly coupled dusty plasma system in an argon dc glow discharge plasma. In particular, measurements of the growth, saturation, and, then, damping of the wave mode as the wave propagates through the cloud are reported. It is observed that the wave amplitude initially exhibits rapid growth while the wavefront compresses. After this initial growth, the width of the wavefront remains relatively constant, while the amplitude of the wavefront evolves like the background dust medium. In some cases, it is also observed that the wave amplitude can decay more quickly than the background dust medium.

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Doro, Emmanuel O., and Cyrus K. Aidun. "Interfacial waves and the dynamics of backflow in falling liquid films." Journal of Fluid Mechanics 726 (May 31, 2013): 261–84. http://dx.doi.org/10.1017/jfm.2013.172.

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AbstractBy studying the dynamics of the streamwise pressure gradient at the wavefront of travelling interfacial waves, we investigate the formation and evolution of backflow regions for the sinusoidal and teardrop-shaped surface wave regimes of laminar falling liquid films. The magnitude of the wavefront streamwise pressure gradient grows as the flow inlet disturbance increases in amplitude and steepness. At large enough values, the adverse pressure gradient induces flow separation and subsequently backflow at the large-amplitude wavefront. The backflow region evolves from a closed circulation to an open vortex as the wave grows to saturation. The dynamics of the streamwise pressure gradient at the sinusoidal wavefront approaches a stable fixed point at saturation. Thus, the open vortex retains its structure as the wave continues downstream. The streamwise pressure gradient at the wavefront of the teardrop-shaped pulse evolves similarly to a time-periodic function with multiple minima/maxima. This phenomenon is a consequence of the interaction between the teardrop-shaped wave and newly formed preceding capillary waves. The nature of the teardrop pulse–capillary wave interaction is such that a decrease in magnitude of the streamwise pressure gradient at the teardrop-shaped wavefront is followed by an increase at the capillary wavefront and vice versa. The increased adverse pressure gradient at the capillary wavefront induces a second open vortex backflow, while the teardrop-shaped wavefront’s open vortex reverts to a closed circulation. This interaction between the waves continues as the teardrop pulse–capillary wavetrain travels downstream, leading to multiple capillary waves and backflow regions.

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Pandey, Alok Kumar, Tanguy Larrieu, Guillaume Dovillaire, Sophie Kazamias, and Olivier Guilbaud. "Shack-Hartmann Wavefront Sensing of Ultrashort Optical Vortices." Sensors 22, no. 1 (December 25, 2021): 132. http://dx.doi.org/10.3390/s22010132.

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Light beams carrying Orbital Angular Momentum (OAM), also known as optical vortices (OV), have led to fascinating new developments in fields ranging from quantum communication to novel light–matter interaction aspects. Even though several techniques have emerged to synthesize these structured-beams, their detection, in particular, single-shot amplitude, wavefront, and modal content characterization, remains a challenging task. Here, we report the single-shot amplitude, wavefront, and modal content characterization of ultrashort OV using a Shack-Hartmann wavefront sensor. These vortex beams are obtained using spiral phase plates (SPPs) that are frequently used for high-intensity applications. The reconstructed wavefronts display a helical structure compatible with the topological charge induced by the SPPs. We affirm the accuracy of the optical field reconstruction by the wavefront sensor through an excellent agreement between the numerically backpropagated and experimentally obtained intensity distribution at the waist. Consequently, through Laguerre–Gauss (LG) decomposition of the reconstructed fields, we reveal the radial and azimuthal mode composition of vortex beams under different conditions. The potential of our method is further illustrated by characterizing asymmetric Gaussian vortices carrying fractional average OAM, and a realtime topological charge measurement at a 10Hz repetition rate. These results can promote Shack-Hartmann wavefront sensing as a single-shot OV characterization tool.

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Nuno, M. Gonçalves, Manuel Abreu, and D. Castro Alves. "Comparison between the scanning pentaprism and the Hartman method for wavefront analysis." Journal of Physics: Conference Series 2407, no. 1 (December 1, 2022): 012014. http://dx.doi.org/10.1088/1742-6596/2407/1/012014.

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Abstract Techniques for wavefront measurement have many applications as optics systems for astronomy and as verification tests for optical surfaces. The development of large aperture optical systems drives the search for low cost and high-resolution wavefront detection sensors. The Hartman technique and its variations (i.e the Shack-Hartman sensor) are the current standards for the characterization of low-order optical aberrations, such as defocus and spherical. The scanning pentaprism method is presented as a simple and low-cost method for the verification of such aberrations. In this method, a transverse section of a wavefront is scanned and sampled into a series of sub-wavefronts with smaller apertures. The relative positions of the produced centroids are measured relative to a calibrated position. This allows for the determination of the optical path difference along the section and consequently the wavefront error. Both techniques were used as tools for collimating a telescope that is part of the on-ground support equipment of ESA PLATO mission. In this work, the results from both methodologies are compared.

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Carcione, José M. "Wavefronts in dissipative anisotropic media." GEOPHYSICS 59, no. 4 (April 1994): 644–57. http://dx.doi.org/10.1190/1.1443624.

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The purpose of this work is to draw attention to several differences between wave propagation in dis, sipative anisotropic media and purely elastic anisotropic media. In an elastic medium, the wavefront is defined as the envelope of the family of planes that makes the phase of the plane waves zero. It turns out that this definition coincides with the wavefronts obtained from the group and energy velocities, i.e., the three concepts are equivalent. However, for plane waves traveling in dissipative anisotropic media these concepts are different. Despite these differences, the velocity of the envelope of plane waves closely approximates the energy velocity, and therefore can represent the wavefront from a practical point of view. On the other hand, the group velocity describes the wavefront only when the attenuation is relatively low, i.e., for Q values higher than 100. The values of the different velocities and the shape of the wavefront are considerably influenced by the relative values of the attenuation along the principal axes of the anisotropic medium. This means that the anisotropic coefficients in attenuating anisotropic media may differ substantially from the corresponding elastic coefficients. Moteover, it is shown that the usual orthogonality properties between the slowness surface and energy velocity vector and the wavefront and wavenumber vector does not hold for dissipative anisotropic media.

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Samoylova, Liubov, Alexey Buzmakov, Oleg Chubar, and Harald Sinn. "WavePropaGator: interactive framework for X-ray free-electron laser optics design and simulations." Journal of Applied Crystallography 49, no. 4 (July 6, 2016): 1347–55. http://dx.doi.org/10.1107/s160057671600995x.

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This article describes theWavePropaGator(WPG) package, a new interactive software framework for coherent and partially coherent X-ray wavefront propagation simulations. The package has been developed at European XFEL for users at the existing and emerging free-electron laser (FEL) facilities, as well as at the third-generation synchrotron sources and future diffraction-limited storage rings. TheWPGaddresses the needs of beamline scientists and user groups to facilitate the design, optimization and improvement of X-ray optics to meet their experimental requirements. The package uses theSynchrotron Radiation Workshop(SRW) C/C++ library and its Python binding for numerical wavefront propagation simulations. The framework runs reliably under Linux, Microsoft Windows 7 and Apple Mac OS X and is distributed under an open-source license. The available tools allow for varying source parameters and optics layouts and visualizing the results interactively. The wavefront history structure can be used for tracking changes in every particular wavefront during propagation. The batch propagation mode enables processing of multiple wavefronts in workflow mode. The paper presents a general description of the package and gives some recent application examples, including modeling of full X-ray FEL beamlines and start-to-end simulation of experiments.

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G.S.M., Jansen, Freisem L., Rudolf D., Eikema K.S.E., and Witte S. "Spectrally resolved wavefront characterization of broadband ultrafast high-harmonic pulses." EPJ Web of Conferences 205 (2019): 01022. http://dx.doi.org/10.1051/epjconf/201920501022.

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We demonstrate a sensor that measures wavefronts of multiple extreme ultraviolet wavelengths simultaneously. By incorporating transmission gratings into the apertures of a Hartmann mask, we can record wavefront information for series of discrete harmonics from a high-harmonic generation source in a single camera exposure, without the need for scanning parts. Wavefronts of up to nine high harmonics at 25-49 nm wavelength are retrieved, and ultrafast spatiotemporal couplings can be detected.

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Wang, Juan. "Fast Algorithm of the Traveltime Calculation Based on Binomial Heap Sorts." Advanced Materials Research 267 (June 2011): 857–61. http://dx.doi.org/10.4028/www.scientific.net/amr.267.857.

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Traveltime calculation has been applied in many project extensively such as earthquake simulation, prestack migration, tomographic imaging, velocity analysis. finite-difference solution of the eikonal equation along expanding wavefronts had two prominent characteristics:one was wavefront points update very frequent, Usually insert some new wavefronts points after extacting one minimum point every time;the other was that the new calculated wavefronts’s traveltime was usually large.Therefore,the paper introduced binomial heap sorts method, optimizated the method of inserting new wavefronts and removing the minimum point in wavefronts, ensured the search efficiency, and had good time complexity.

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Feuillade, C. "Wavefront scatter and wavefront healing." Journal of the Acoustical Society of America 109, no. 5 (May 2001): 2299. http://dx.doi.org/10.1121/1.4744065.

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Mei, Ming, Joseph W. H. So, Michael Y. Li, and Samuel S. P. Shen. "Asymptotic stability of travelling waves for Nicholson's blowflies equation with diffusion." Proceedings of the Royal Society of Edinburgh: Section A Mathematics 134, no. 3 (June 2004): 579–94. http://dx.doi.org/10.1017/s0308210500003358.

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This paper considers the nonlinear stability oftravelling wavefronts of a time-delayed diffusive Nicholson blowflies equation. We prove that, under a weighted L2 norm, ifa solution is sufficiently close to a travelling wave front initially, it converges exponentially to the wavefront as t → ∞. The rate ofconvergence is also estimated.

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Carmichael Martins, Alessandra, and Brian Vohnsen. "Measuring Ocular Aberrations Sequentially Using a Digital Micromirror Device." Micromachines 10, no. 2 (February 12, 2019): 117. http://dx.doi.org/10.3390/mi10020117.

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The Hartmann–Shack wavefront sensor is widely used to measure aberrations in both astronomy and ophthalmology. Yet, the dynamic range of the sensor is limited by cross-talk between adjacent lenslets. In this study, we explore ocular aberration measurements with a recently-proposed variant of the sensor that makes use of a digital micromirror device for sequential aperture scanning of the pupil, thereby avoiding the use of a lenslet array. We report on results with the sensor using two different detectors, a lateral position sensor and a charge-coupled device (CCD) scientific camera, and explore the pros and cons of both. Wavefront measurements of a highly aberrated artificial eye and of five real eyes, including a highly myopic subject, are demonstrated, and the role of pupil sampling density, CCD pixel binning, and scanning speed are explored. We find that the lateral position sensor is mostly suited for high-power applications, whereas the CCD camera with pixel binning performs consistently well both with the artificial eye and for real-eye measurements, and can outperform a commonly-used wavefront sensor with highly aberrated wavefronts.

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Pierpont, Gordon L., Sumeet S. Chugh, John A. Hauck, and Charles C. Gornick. "Endocardial activation during ventricular fibrillation in normal and failing canine hearts." American Journal of Physiology-Heart and Circulatory Physiology 279, no. 4 (October 1, 2000): H1737—H1747. http://dx.doi.org/10.1152/ajpheart.2000.279.4.h1737.

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Because congestive heart failure (CHF) promotes ventricular fibrillation (VF), we compared VF in seven dogs with CHF induced by combined myocardial infarction and rapid ventricular pacing to VF in six normal dogs. A noncontact, multielectrode array balloon catheter provided full-surface real-time left ventricular (LV) endocardial electrograms and a dynamic color-coded display of endocardial activation projected onto a three-dimensional model of the LV. Fast Fourier transform (FFT) analysis of virtual electrograms showed no difference in peak or centroid frequency in CHF dogs compared with normals. The average number of simultaneous noncontiguous wavefronts present during VF was higher in normals (2.4 ± 1.0 at 10 s of VF) than in CHF dogs (1.3 ± 1.0, P < 0.005) and decreased in both over time. The wavefront “turnover” rate, estimated using FFT of the noncontiguous wavefront data, did not differ between normals and CHF and did not change over 5 min of VF. Thus the fundamental frequency characteristics of VF are unaltered by CHF, but dilated abnormal ventricles sustain fewer active wavefronts than do normal ventricles.

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Li, Shiqing, Zhuo Wang, Shaohua Dong, Sixiong Yi, Fuxin Guan, Yizhen Chen, Huijie Guo, Qiong He, Lei Zhou, and Shulin Sun. "Helicity-delinked manipulations on surface waves and propagating waves by metasurfaces." Nanophotonics 9, no. 10 (July 4, 2020): 3473–81. http://dx.doi.org/10.1515/nanoph-2020-0200.

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AbstractAlthough many approaches have been proposed to manipulate propagating waves (PWs) and surface waves (SWs), usually each operation needs a separate meta-device, being unfavorable for optical integrations. Here, we propose a scheme to design a single meta-device that can efficiently generate SWs and/or PWs with pre-designed wavefronts, under the excitations of circularly polarized (CP) PWs with different helicity. As a proof of concept, we design and fabricate a microwave meta-device and experimentally demonstrate that it can convert incident CP waves of opposite helicity to SWs possessing different wavefronts and traveling to opposite directions, both exhibiting very high efficiencies. We further generalize our scheme to design a meta-device and numerically demonstrate that it can either excite a SW beam with tailored wavefront or generate a far-field PW with pre-designed wavefront, as shined by CP waves with different helicity. Our work opens the door to achieving simultaneous controls on far- and near-field electromagnetic environments based on a single ultra-compact platform.

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Cheng, Kang-An, Derek J. Dosdall, Li Li, Jack M. Rogers, Raymond E. Ideker, and Jian Huang. "Evolution of activation patterns during long-duration ventricular fibrillation in pigs." American Journal of Physiology-Heart and Circulatory Physiology 302, no. 4 (February 15, 2012): H992—H1002. http://dx.doi.org/10.1152/ajpheart.00419.2011.

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Quantitative analysis has demonstrated five temporal stages of activation during the first 10 min of ventricular fibrillation (VF) in dogs. To determine whether these stages exist in another species, we applied the same analysis to the first 10 min of VF recorded in vivo from two 504-electrode arrays, one each on left anterior and posterior ventricular epicardium in six anesthetized pigs. The following descriptors were continuously quantified: 1) number of wavefronts, 2) wavefront fractionations, 3) wavefront collisions, 4) repeatability, 5) multiplicity index, 6) wavefront conduction velocity, 7) activation rate, 8) mean area activated by the wavefronts, 9) negative peak rate of voltage change, 10) incidence of breakthrough/foci, 11) incidence of block, and 12) incidence of reentry. Cluster analysis of these descriptors divided VF into four stages ( stages i-iv). The values of most descriptors increased during stage i (1–22 s after VF induction), changed quickly to values indicating greater organization during stage ii (23–39 s), decreased steadily during stage iii (40–187 s), and remained relatively unchanged during stage iv (188–600 s). The epicardium still activated during stage iv instead of becoming silent as in dogs. In conclusion, during the first 10 min, VF activation can be divided into four stages in pigs instead of five stages as in dogs. Following a 16-s period during the first minute of VF when activation became more organized, all parameters exhibited progressive decreased organization. Further studies are warranted to determine whether these changes, particularly the increased organization of stage ii, have clinical consequences, such as alteration in defibrillation efficacy.

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Fuerst, Martin E., and Georg Schitter. "Scanning Wavefront Sensor for Measurement of Highly Divergent Wavefronts." IFAC-PapersOnLine 52, no. 15 (2019): 25–30. http://dx.doi.org/10.1016/j.ifacol.2019.11.644.

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Ahmadi, Kavan, and Artur Carnicer. "Estimation of Zernike polynomials for a highly focused electromagnetic field using polarimetric mapping images and neural networks." Journal of Physics: Conference Series 2407, no. 1 (December 1, 2022): 012002. http://dx.doi.org/10.1088/1742-6596/2407/1/012002.

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Abstract In this communication, we present a method to estimate the aberrated wavefront at the focal plane of a vectorial diffraction system. In contrast to the phase, the polarization state of optical fields is simply measurable. In this regard, we introduce an alternative approach for determining the aberration of the wavefront using polarimetric information. The method is based on training a convolutional neural network using a large set of polarimetric mapping images obtained by simulating the propagation of aberrated wavefronts through a high-NA microscope objective; then, the coefficients of the Zernike polynomials could be recovered after interrogating the trained network. On the one hand, our approach aims to eliminate the necessity of phase retrieval for wavefront sensing applications, provided the beam used is known. On the other hand, the approach might be applied for calibrating the complex optical system suffering from aberrations. As proof of concept, we use a radially polarized Gaussian-like beam multiplied by a phase term that describes the wavefront aberration. The training dataset is produced by using Zernike polynomials with random coefficients. Two thousand random combinations of polynomial coefficients are simulated. For each one, the Stokes parameters are calculated to introduce a polarimetric mapping image as the input of a neural network model designed and trained for predicting the polynomial coefficients. The accuracy of the neural network model is tested by predicting an unseen dataset (test dataset) with a high success rate.

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Serra, Jean. "MORPHOLOGICAL DESCRIPTIONS USING THREE-DIMENSIONAL WAVEFRONTS." Image Analysis & Stereology 21, no. 4 (May 3, 2011): 13. http://dx.doi.org/10.5566/ias.v21.ps13-s21.

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The present study deals with the analysis of three-dimensional binary objects whose structure is not obvious nor generally clearly visible. Our approach is illustrated through three examples taken from biological microscopy. In one of our examples, we need to extract the osteocytes contained in sixty confocal sections. The cells are not numerous, but are characterized by long branches, hence they will be separated using a directional wavefront The two other objects are more complex and will be analysed by means of a spherical wavefront In the first case, a kidney of a rat embryo, the tissue grows like a tree, where we want to detect the branches, their extremities,and their spatial arrangement. The wavefront method enables us to define precisely branches and extremities, and gives flexible algorithms. The last example deals with the embryonic growth of the chicken shinbone. The central part of the bone (or shaft) is structured as a series of nested cylinders following the same axis, and connected by more or less long bridges. Using wavefronts, we show that it is possible to separate the cylinders,and to extract and count the bridges that connect them.

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Cheng, Arthur C. K. "Wavefront-guided versus wavefront-optimized treatment." Journal of Cataract & Refractive Surgery 34, no. 8 (August 2008): 1229–30. http://dx.doi.org/10.1016/j.jcrs.2008.04.035.

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Liang, Jianjun, Xiao-Ming Li, and Kaiguo Fan. "Distribution and Source Sites of Nonlinear Internal Waves Northeast of Hainan Island." Journal of Marine Science and Engineering 10, no. 1 (January 4, 2022): 55. http://dx.doi.org/10.3390/jmse10010055.

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The distribution and source sites of nonlinear internal waves (NLIWs) northeast of Hainan Island were investigated using satellite observations and a wavefront propagation model. Satellite observations show two types of NLIWs (here referred to as type-S and type-D waves). The type-S waves are spaced at a semidiurnal tidal period and the type-D waves are spaced at a diurnal tidal period. The spatial distribution of the two types of NLIWs displays a sandwich structure in which the middle region is influenced by both types of NLIWs, and the northern and southern regions are governed by the type-S and type-D waves, respectively. Solving the wavefront model yields good agreement between simulated and observed wavefronts from the Luzon Strait to Hainan Island. We conclude that the NLIWs originate from the Luzon Strait.

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Yuan, Zhu, Yunji Meng, Weiliang Ma, Runkun Chen, Tao Wang, and Peining Li. "Near-field mapping of complex-valued wavevectors of in-plane hyperbolic phonon polaritons in α-MoO₃." Applied Physics Letters 120, no. 13 (March 28, 2022): 131105. http://dx.doi.org/10.1063/5.0078210.

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Hyperbolic phonon polaritons (HPhPs) in α-phase molybdenum trioxide (α-MoO3) have recently attracted significant attention. They propagate anisotropically along the flake of α-MoO3 and show anomalously concave wavefronts when being excited by a pointlike source. Such anisotropic propagation is governed by the anisotropic wavevectors of HPhPs, which have been studied in different works. However, extracting the complex-valued wavevectors of all HPhP modes directly from the observed anomalous wavefront remains elusive. Here, we theoretically and experimentally demonstrate that the complex-valued HPhP wavevectors can be accurately quantified by fitting the concave wavefront profiles with a modified damped sine-wave function in all allowed directions. To that end, HPhPs are launched by an infrared antenna on a thin flake of α-MoO3 and are imaged in real space by using scanning near-field optical microscope. From the recorded concave wavefronts of HPhPs, we have experimentally retraced both the real part and the imaginary part of polariton wavevectors along different propagation directions. Our results are of fundamental importance for analyzing the optical properties of HPhPs in α-MoO3, which can also be generic to other anisotropic optical/polaritonic systems.

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Singh, Brijesh Kumar, G. Singh, P. Senthilkumaran, and D. S. Mehta. "Generation of Optical Vortex Arrays Using Single-Element Reversed-Wavefront Folding Interferometer." International Journal of Optics 2012 (2012): 1–7. http://dx.doi.org/10.1155/2012/689612.

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Optical vortex arrays have been generated using simple, novel, and stable reversed-wavefront folding interferometer. Two new interferometric configurations were used for generating a variety of optical vortex lattices. In the first interferometric configuration one cube beam splitter (CBS) was used in one arm of Mach-Zehnder interferometer for splitting and combining the collimated beam, and one mirror of another arm is replaced by second CBS. At the output of interferometer, three-beam interference gives rise to optical vortex arrays. In second interferometric configuration, a divergent wavefront was made incident on a single CBS which splits and combines wavefronts leading to the generation of vortex arrays due to four-beam interference. It was found that the orientation and structure of the optical vortices can be stably controlled by means of changing the rotation angle of CBS.

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BIKTASHEVA, I. V., V. N. BIKTASHEV, W. N. DAWES, A. V. HOLDEN, R. C. SAUMAREZ, and A. M. SAVILL. "DISSIPATION OF THE EXCITATION FRONT AS A MECHANISM OF SELF-TERMINATING ARRHYTHMIAS." International Journal of Bifurcation and Chaos 13, no. 12 (December 2003): 3645–55. http://dx.doi.org/10.1142/s0218127403008909.

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The dissipation of the excitation wavefronts is a specific mechanism of propagation failure if the sharp gradient of the transmembrane voltage at the wavefront smears out and spread of voltage becomes diffusive, as the main excitation current becomes inactivated. This is produced by the normal kinetics of the ionic currents underlying the action potential. Here we demonstrate that the dissipation of the excitation wavefront can cause arrhythmia as well as lead to its self-termination. We use Courtemanche et al. model of human atrial action potential to demonstrate how reentry creates dynamic electrophysiologic inhomogeneity of the tissue. Local dissipation of the excitation front causes wave breaks and instantaneous displacement of the tip of the reentry, and the same mechanism can lead to elimination of all wavelets, as the inhomogeneity creates conditions for simultaneous dissipation of their excitation fronts.

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Khonina, Svetlana N., Sergey V. Karpeev, and Alexey P. Porfirev. "Wavefront Aberration Sensor Based on a Multichannel Diffractive Optical Element." Sensors 20, no. 14 (July 10, 2020): 3850. http://dx.doi.org/10.3390/s20143850.

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We propose a new type of a wavefront aberration sensor, that is, a Zernike matched multichannel diffractive optical filter, which performs consistent filtering of phase distributions corresponding to Zernike polynomials. The sensitivity of the new sensor is theoretically estimated. Based on the theory, we develop recommendations for its application. Test wavefronts formed using a spatial light modulator are experimentally investigated. The applicability of the new sensor for the fine-tuning of a laser collimator is assessed.

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... "Wavefront-Kılavuzlu ve Wavefront-Optimize Lazer Tedavileri." Türk Oftalmoloji Dergisi 42, no. 6 (December 15, 2012): 474–78. http://dx.doi.org/10.4274/tjo.42.72792.

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Spagnolini, U. "Nonparametric narrowband wavefront estimation from wavefront gradients." IEEE Transactions on Signal Processing 47, no. 11 (1999): 3116–21. http://dx.doi.org/10.1109/78.796444.

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COCHENER, B. "Wavefront guided and custom wavefront refractive surgery." Acta Ophthalmologica 88 (September 2010): 0. http://dx.doi.org/10.1111/j.1755-3768.2010.4434.x.

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Rawlinson, N., and M. Sambridge. "Multiple reflection and transmission phases in complex layered media using a multistage fast marching method." GEOPHYSICS 69, no. 5 (September 2004): 1338–50. http://dx.doi.org/10.1190/1.1801950.

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Traditional grid‐based eikonal schemes for computing traveltimes are usually confined to obtaining first arrivals only. However, later arrivals can be numerous and of greater amplitude, making them a potentially valuable resource for practical applications such as seismic imaging. The aim of this paper is to introduce a grid‐based method for tracking multivalued wavefronts composed of any number of reflection and refraction branches in layered media. A finite‐difference eikonal solver known as the fast marching method (FMM) is used to propagate wavefronts from one interface to the next. By treating each layer that the wavefront enters as a separate computational domain, one obtains a refracted branch by reinitializing FMM in the adjacent layer and a reflected branch by reinitializing FMM in the incident layer. To improve accuracy, a local grid refinement scheme is used in the vicinity of the source where wavefront curvature is high. Several examples are presented which demonstrate the viability of the new method in highly complex layered media. Even in the presence of velocity variations as large as 8:1 and interfaces of high curvature, wavefronts composed of many reflection and transmission events are tracked rapidly and accurately. This is because the scheme retains the two desirable properties of a single‐stage FMM: computational speed and stability. Local grid refinement about the source also can increase accuracy by an order of magnitude with little increase in computational cost.

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Chambouleyron, V., O. Fauvarque, P. Janin-Potiron, C. Correia, J.-F. Sauvage, N. Schwartz, B. Neichel, and T. Fusco. "Pyramid wavefront sensor optical gains compensation using a convolutional model." Astronomy & Astrophysics 644 (November 24, 2020): A6. http://dx.doi.org/10.1051/0004-6361/202037836.

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Context. Extremely large telescopes are overwhelmingly equipped with pyramid wavefront sensors (PyWFS) over the more widely used Shack–Hartmann wavefront sensor to perform their single-conjugate adaptive optics (SCAO) mode. The PyWFS, a sensor based on Fourier filtering, has proven to be highly successful in many astronomy applications. However, this sensor exhibits non-linear behaviours that lead to a reduction of the sensitivity of the instrument when working with non-zero residual wavefronts. This so-called optical gains (OG) effect, degrades the closed-loop performance of SCAO systems and prevents accurate correction of non-common path aberrations (NCPA). Aims. In this paper, we aim to compute the OG using a fast and agile strategy to control PyWFS measurements in adaptive optics closed-loop systems. Methods. Using a novel theoretical description of PyWFS, which is based on a convolutional model, we are able to analytically predict the behaviour of the PyWFS in closed-loop operation. This model enables us to explore the impact of residual wavefront errors on particular aspects such as sensitivity and associated OG. The proposed method relies on the knowledge of the residual wavefront statistics and enables automatic estimation of the current OG. End-to-end numerical simulations are used to validate our predictions and test the relevance of our approach. Results. We demonstrate, using on non-invasive strategy, that our method provides an accurate estimation of the OG. The model itself only requires adaptive optics telemetry data to derive statistical information on atmospheric turbulence. Furthermore, we show that by only using an estimation of the current Fried parameter r0 and the basic system-level characteristics, OGs can be estimated with an accuracy of less than 10%. Finally, we highlight the importance of OG estimation in the case of NCPA compensation. The proposed method is applied to the PyWFS. However, it remains valid for any wavefront sensor based on Fourier filtering subject from OG variations.

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Doskolovich, L. L., D. A. Bykov, A. A. Mingazov, and E. A. Bezus. "Method for calculating a refractive optical element forming given illuminance distribution and wavefront." Computer Optics 45, no. 6 (November 2021): 818–27. http://dx.doi.org/10.18287/2412-6179-co-912.

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In the geometrical optics approximation, we consider a method for calculating a refractive optical element with two freeform surfaces, which transforms an incident beam with a plane wave-front into an output beam with a required wavefront and generating a required illuminance distribution. As examples, optical elements forming given illuminance distributions and (converging and diverging) spherical wavefronts are designed. The presented examples demonstrate the good performance of the method.

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Yang, Jinsheng, Ling Wei, Hongli Chen, Xuejun Rao, and Changhui Rao. "Absolute calibration of Hartmann-Shack wavefront sensor by spherical wavefronts." Optics Communications 283, no. 6 (March 2010): 910–16. http://dx.doi.org/10.1016/j.optcom.2009.11.022.

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Salamone, Joseph A. "Three-dimensional wavefront modeling of secondary sonic booms." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A85. http://dx.doi.org/10.1121/10.0010739.

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There is an abundance of previous work in the literature regarding the Mach cone of a supersonic vehicle and its associated ground intercepts identifying where and when the primary sonic boom reaches the ground. Likewise, there is excellent past research that models where the secondary sonic boom reaches the ground due to the reflection and refraction of the sonic boom emanating from above and below a supersonic vehicle. This work will provide a bridge between the two aforementioned aspects of past research. The Mach cone for both above the aircraft and below the aircraft after it reaches the ground will be extended to model the three-dimensional wavefront evolution of the secondary sonic boom as it propagates to the ground. The secondary sonic boom wavefronts modeled in this work will only consist of rays that refract in the vicinity of the stratosphere. The present work will show several cases of the secondary sonic boom wavefront propagation in three dimensions for a variety of aircraft headings and geographic locations around the world with representative upper air temperature and wind conditions.

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Zhang, Zhentao, Nazim Bharmal, Tim Morris, and Yonghui Liang. "Laboratory quantification of a plenoptic wavefront sensor with extended objects." Monthly Notices of the Royal Astronomical Society 497, no. 4 (August 5, 2020): 4580–86. http://dx.doi.org/10.1093/mnras/staa2269.

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ABSTRACT Adaptive optics (AO) is widely used in ground-based telescopes to compensate the effects of atmosphere distortion, and the wavefront sensor is a significant component in the AO systems. The plenoptic wavefront sensor has been proposed as an alternative wavefront sensor adequate for extended objects and wide field of views. In this paper, a experimental bench has been set up to investigate the slope measurement accuracy and closed-loop wavefront correction performance for extended objects. From the experimental results, it has been confirmed that plenoptic wavefront sensor is suitable for extended objects wavefront sensing with proper optical design. The slope measurements have a good linearity and accuracy when observing extended objects. The image quality is significantly improved after closed-loop correction. A method of global tip/tilt measurement using only plenoptic wavefront sensor frame is proposed in this paper, it is also a potential advantage of plenoptic wavefront sensor in extended objects wavefront sensing.

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Van Grinsven, Kari L., Alireza Ousati Ashtiani, and Hongrui Jiang. "Flexible Electrowetting-on-Dielectric Microlens Array Sheet." Micromachines 10, no. 7 (July 11, 2019): 464. http://dx.doi.org/10.3390/mi10070464.

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We have fabricated a fully-flexible, focus-tunable microlens array on a sheet and demonstrated its imaging capabilities. Each liquid lens of the array is individually tunable via electrowetting on dielectric (EWOD) actuation and is situated on a polydimethylsiloxane (PDMS) substrate, which allows the lens array to operate as a reconfigurable optical system. In particular, we observed a significant increase in the field of view (FOV) of the system to 40.4° by wrapping it on a cylindrical surface as compared to the FOV of 21.5° obtained by the array on a planer surface. We also characterized the liquid lenses of the system, observing a range of focus length from 20.2 mm to 9.2 mm as increased voltage was applied to each EWOD lens. A Shack–Hartmann wavefront sensor (SHWS) was used to measure the wavefront of the lens as it was actuated, and the aberrations of the lens were assessed by reporting the Zernike coefficients of the wavefronts.

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Yajima, Takahiro, and Hiroyuki Nagahama. "Finsler geometry of seismic ray path in anisotropic media." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 465, no. 2106 (March 11, 2009): 1763–77. http://dx.doi.org/10.1098/rspa.2008.0453.

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The seismic ray theory in anisotropic inhomogeneous media is studied based on non-Euclidean geometry called Finsler geometry. For a two-dimensional ray path, the seismic wavefront in anisotropic media can be geometrically expressed by Finslerian parameters. By using elasticity constants of a real rock, the Finslerian parameters are estimated from a wavefront propagating in the rock. As a result, the anisotropic parameters indicate that the shape of wavefront is expressed not by a circle but by a convex curve called a superellipse. This deviation from the circle as an isotropic wavefront can be characterized by a roughness of wavefront. The roughness parameter of the real rock shows that the shape of the wavefront is expressed by a fractal curve. From an orthogonality of the wavefront and the ray, the seismic wavefront in anisotropic media relates to a fractal structure of the ray path.

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Xie, Yujiang, and Dirk Gajewski. "Reliability of data-driven wavefront attributes in laterally heterogeneous media." GEOPHYSICS 84, no. 3 (May 1, 2019): O49—O62. http://dx.doi.org/10.1190/geo2018-0382.1.

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3D wavefront attributes play a major role in many processing steps, such as prestack data enhancement, diffraction separation, and wavefront tomography. For the determination of the 3D wavefront attributes, various stacking operators can be used by adopting semblance optimization. These operators are derived for laterally homogeneous media. In praxis, however, they are applied in real geologic environments with even strong lateral velocity variations such as salt structures. This leads to the question of the quality of the 3D wavefront attributes using these operators when determined in the presence of strong lateral velocity changes. We compared the 3D wavefront attributes determined by 3D common-reflection-surface (CRS) operator (called data-driven wavefront attributes) with the 3D wavefront attributes computed by 3D kinematic and dynamic ray tracing (called model-driven wavefront attributes). For the determination of the 3D CRS wavefront attributes, we have developed a global optimization scheme based on differential evolution. Reflection seismic data of the laterally heterogeneous 3D SEG C3WA salt model are considered, and the model-driven wavefront attributes are computed for a smoothed version of the 3D SEG salt model. The comparison reveals that the wavefront attributes for the normal-incidence-point ray indicate a very good match not only in areas of mild lateral velocity variation but even in regions with strong lateral velocity variations. Approximately 80%–90% of the total picks indicate the good match with a relative error of less than 10% when a semblance threshold of 0.1 is considered in the automatic picking process. This confirms the validity of the determined wavefront attributes even in the presence of strong lateral velocity changes. Using a higher semblance threshold in the automatic picking leads to fewer picks but with an even better match between model- and data-driven wavefront attributes.

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Takato, N., M. Iye, and I. Yamaguchi. "Wavefront reconstruction error of Shack-Hartmann wavefront sensors." Publications of the Astronomical Society of the Pacific 106 (February 1994): 182. http://dx.doi.org/10.1086/133367.

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Journal articles on the topic 'Wavefront'

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