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The accuracy of ultrasonic nondestructive examination is limited by the limitation of near field diffraction. With the development of nearfield optical, angular spectrum method is introduced into the acoustic field, which provides a significant direction for the ultrasonic diffraction limit resolution detection. The main research of this paper is the transmission of near field ultrasound in thin workpiece and the law of the interaction of tiny flaws. The paper establishes the relationship between the longitudinal wave signal and the structure of the workpiece and the types of flaws. A method is found that whether there are flaws can be determined near field area by analysing the acoustic field characteristics of workpiece surface. Finally, comparing the calculation results with the finite element simulation, they verify each other, the method turns out to be correct in this paper. The model can also be used to improve the ultrasonic noise reduction algorithm and the extraction of minimal defect feature. It has a greatly practical significance. [ABSTRACT FROM AUTHOR]

An O-shaped structure at wavelengths of 930–960 nm in the frequency–angular spectrum of the supercontinuum generated during the filamentation of a femtosecond laser pulse with a central wavelength of 740 nm on a 75-m path in air has been observed experimentally. This feature of the frequency–angular spectrum is due to the presence of the absorption band of water vapor in the range of 930–960 nm and the anomalous dispersion region associated with this absorption. This result opens prospects for the remote single-pulse detection of impurities in air. [ABSTRACT FROM AUTHOR]

The multi-directionality of polished surface topography (PST) is a key index to characterize the polished surface quality and surface integrity, and its prediction before actual machining is of great significance to the toolpath planning, verification, and optimization. However, most related works reported thus far focus mainly on the material removal modeling but few on the prediction of multi-directionality. Hence, this paper proposes a rapid method to precisely predict the multi-directionality of the PST for the pad-polishing process of freeform surfaces. With this method, a pressure distribution model and a material removal profile (MRP) model are first established, in which the MRP is founded subject to the quadratic function distribution. Then, to avoid time-consuming integral operation in the MRP model, an artificial neural network is developed to fit the quadratic function of MRP. With this model, a multi-directionality prediction algorithm is further proposed based on the angular spectrum of the PST. Simulation and experimental studies have shown that the proposed method can predict the multi-directionality of the PST with very high accuracy and efficiency for freeform surface polishing, showing great application potential in promoting the efficiency of toolpath planning and optimization. [ABSTRACT FROM AUTHOR]

Optical interference is not only a fundamental phenomenon that has enabled new theories of light to be derived but it has also been used in interferometry for the measurement of small displacements, refractive index changes, and surface irregularities. In a two-beam interferometer, variations in the interference fringes are used as a diagnostic for anything that causes the optical path difference (OPD) to change; therefore, for a specified OPD, greater variation in the fringes indicates better measurement sensitivity. Here, we introduce and experimentally validate an interesting optical interference phenomenon that uses photons with a structured frequency-angular spectrum, which are generated from a spontaneous parametric down-conversion process in a nonlinear crystal. This interference phenomenon is manifested as interference fringes that vary much more rapidly with increasing OPD than the corresponding fringes for equal-inclination interference; the phenomenon is parameterised using an equivalent wavelength, which under our experimental conditions is 29.38 nm or about 1/27 of the real wavelength. This phenomenon not only enriches the knowledge with regard to optical interference but also offers promise for applications in interferometry., (© 2021. The Author(s).)

The InSightec Exablate system is the standard of care used for transcranial focused ultrasound ablation treatments in the United States. The system calculates phase corrections that account for aberrations caused by the human skull. This work investigates whether skull aberration correction can be improved by comparing the standard of care InSightec ray tracing method with the hybrid angular spectrum (HAS) method and the gold standard hydrophone method. Three degassed ex vivo human skulls were sonicated with a 670 kHz hemispherical phased array transducer (InSightec Exablate 4000). Phase corrections were calculated using four different methods (straight ray tracing, InSightec ray tracing, HAS, and hydrophone) and were used to drive the transducer. 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. For three skulls, the InSightec ray tracing method achieved 52 ± 21% normalized target intensity (normalized to hydrophone), 76 ± 17% normalized peak intensity, and 0.72 ± 0.47 mm positioning error. The HAS method achieved 74 ± 9% normalized target intensity, 81 ± 9% normalized peak intensity, and 0.35 ± 0.09 mm positioning error. The InSightec-to-HAS improvement in focal spot targeting provides promise in improving treatment outcomes. These improvements to skull aberration correction are also highly relevant for the applications of focused ultrasound neuromodulation and blood brain barrier opening, which are currently being translated for human use. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai Jiaotong University (Science) is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Terahertz digital holography (THz-DH) has the potential to be used for non-destructive inspection of visibly opaque soft materials due to its good immunity to optical scattering and absorption. Although previous research on full-field off-axis THz-DH has usually been performed using Fresnel diffraction reconstruction, its minimum reconstruction distance occasionally prevents a sample from being placed near a THz imager to increase the signal-to-noise ratio in the hologram. In this article, we apply the angular spectrum method (ASM) for wavefront reconstruction in full-filed off-axis THz-DH because ASM is more accurate at short reconstruction distances. We demonstrate real-time phase imaging of a visibly opaque plastic sample with a phase resolution power of λ/49 at a frame rate of 3.5 Hz in addition to real-time amplitude imaging. We also perform digital focusing of the amplitude image for the same object with a depth selectivity of 447 μm. Furthermore, 3D imaging of visibly opaque silicon objects was achieved with a depth precision of 1.7 μm. The demonstrated results indicate the high potential of the proposed method for in-line or in-process non-destructive inspection of soft materials. [ABSTRACT FROM AUTHOR]

The influence of the numerical aperture of a light beam that probes a layered object on the magnitude of the quantity measured with a confocal interference microscope upon determining the object thickness has been studied theoretically and experimentally for the case in which the signal is significantly affected by the spherical aberration arising in the probing beam as it passes through the object. The dependence of the quantity to be measured on the numerical aperture is obtained taking into account the influence of the spherical aberration on the signal. The criterion of the "nonaberrational" propagation of the beam probing the object is determined and the condition under which the influence of the spherical aberration on the signal of the confocal microscope can be neglected is found. An approximate analytical expression is obtained, which makes it possible to determine the "nonaberrational" width of the angular spectrum of the light beam probing the object, taking into account an empirical correction factor. The applicability limits of the analytical dependence of the quantity to be measured on the numerical aperture, which has been previously obtained for the case of a negligibly weak influence of the spherical aberration on the signal from the confocal microscope, have been determined. [ABSTRACT FROM AUTHOR]

The effects of the decoherence of a narrow-band optical field with a broad angular spectrum upon propagation through a plate of a transparent medium placed in one of the arms of the Michelson interferometer are established. [ABSTRACT FROM AUTHOR]

In digital holography, two most frequently used numerical reconstruction methods are angular spectrum method (ASM) and Fresnel diffraction method (FDM). Both methods suffer from limitation of propagation distance as ASM is applicable for short distances, while FDM is suitable for long propagation distances. In this article, we revisit our previous work (Dwivedi et al. in J Opt. 10.1007/s12596-017-0424-z) in which we compared ASM and FDM. Here, we made corrections in the equations of numerical reconstruction and distance constraint in ASM. These corrections rectify the error of size variation of reconstructed images with change in recording and corresponding reconstruction propagation distances in ASM. This paper aims to further improve the understanding of both the numerical reconstruction methods and fix limitations of previous work. In present work, we use transparent and diffuse objects to record digital holograms. Apart from results on numerical reconstruction of digital holograms, we also discuss results of reconstruction after filtering in Fourier domain using ASM and FDM and zero padding in ASM. This paper presents an extensive analysis, comparison and suitability of both numerical reconstruction methods for particular applications. [ABSTRACT FROM AUTHOR]

The near-infrared (NIR) imaging method was required for the diagnosis of varicose veins, which mean that the veins have become enlarged and twisted on leg. In some cases, the hair on leg could be dense and formed a noise during the NIR vein images. Here, a preliminary treatment to filter out the effect of hair on the NIR image was carried out. The filter design was based on the optical angular spectrum theory to select a threshold spatial frequency in order to separate a specific vein infrared image of leg from that of the hair. An experimental setup combined a NIR light, a charge coupled device camera with the filtering algorithms which were implemented to prove the effectiveness on the hair noise removal. The results demonstrated that an annulus Butterworth filter was more effective to reduce the hair noise and simultaneously enhance the contrast of the venous images on leg than the others. This design processed a NIR image in terms of an optical angular spectrum theory, thereby an all-optical treatment for the contrast enhancement of a veins image being possible in the future. [ABSTRACT FROM AUTHOR]

The features of the anisotropic acousto-optic Bragg diffraction in paratellurite related to the measurement and control of the angular spectrum of monochromatic optical radiation are analyzed. We consider the diffraction configuration in which a narrow angular component whose position is determined by the frequency of acoustic wave is deflected from the divergent optical beam. The angular spectrum of optical radiation can be measured using variations in the acoustic frequency. It is demonstrated that such a configuration can be used for the measurement of the angular spectrum of light and for the formation of the desired angular distribution. [ABSTRACT FROM AUTHOR]

A closed formula based on representing the angular spectrum in the Fourier basis was obtained for computing the correlation coefficients of signal fadings in elements of the multiantenna system. The method of estimating the expansion coefficients of the angular spectrum with subsequent evaluation of the spatial correlation function was proposed. [ABSTRACT FROM AUTHOR]

Mathematical models and methods for determining the degree of roughness and other parameters of multilayer nanostructures from the angular spectrum of the intensity of the reflected X-rays are studied. The proposed mathematical model for solving the direct problem of x-ray propagation and the distribution of their electromagnetic field within a multilayer nanostructure takes into account the refraction effect due to the inclusion of the second derivative with respect to the structure depth. A numerical method for solving the resulting problem is developed, and the numerical results are analyzed. The approximation-combinatorial method of the decomposition and composition of systems is used to solve the inverse problem. [ABSTRACT FROM AUTHOR]

We have developed an analytic treatment of light emission properties of electric and magnetic multipoles near a planar dielectric surface, using angular spectrum representation of vector spherical waves. The results are described in terms of spatial rotation matrix elements, so that the angular distribution of light emission for higher order multipoles is easily obtained, which enables us to evaluate basic optical near-field problems such as electric dipole radiation with arbitrary orientation with respect both to surface and observation direction. The numerical results are in good agreement with our previous experimental results and the numerical results reported by Lukosz. [ABSTRACT FROM AUTHOR]

We consider the hypothesis of instantaneous volume speckle structures in a partially coherent optical wave field of frequency-broadband radiation from an extended light source. We discuss the spatiotemporal correlation properties of instantaneous speckle structures and the relation of these properties with the spatiotemporal coherent properties of the wave field. We show that the instantaneous speckle structures determine spatial fluctuations of the wave field and its spatial coherent properties. Using numerical calculations of the field of wave perturbations in the near-field diffraction region of the extended light source, we obtain images of instantaneous speckle structures in the longitudinal cross section of the wave field and investigate the correlation properties of the spatial distribution of the instantaneous intensity of the wave field in the direction of its propagation as functions of the width of the frequency spectrum and the width of the angular spectrum of the field. We show that the longitudinal length of instantaneous speckles can be determined either by the width of the frequency spectrum of the field, or the width of its angular spectrum, or, jointly, by the width of the frequency spectrum and the width of the angular spectrum of the field. We find conditions under which instantaneous speckle structures propagate, experiencing decorrelation changes during their propagation, to a distance that is determined by the width of the angular spectrum of the field. [ABSTRACT FROM AUTHOR]

We analyze the state of type-I SPDC polarization in nonlinear uniaxial crystals using a coordinate system connected with a pump beam. The entanglement loss due to the Migdall effect is examined. The analytical expressions for polarization components of the signal and idler waves for the frequency-degenerate regime are obtained. The numerical results for BBO crystal are also adduced. [ABSTRACT FROM AUTHOR]

The angular spectrum of spontaneous emission in a two-dimensional undulator free-electron laser is analyzed theoretically. Numerical calculation shows that the s-th harmonic spontaneous emission power density can be greatly enhanced by using a two-dimensional undulator, for which l=s, so the harmonic number can be selected by selecting l. Therefore, the higher harmonic operation of a free-electron laser can be realized selectively. [ABSTRACT FROM AUTHOR]

For obliquely incident guided modes the light propagation in slab waveguides with step discontinuities can be described by means of an angular-spectrum representation of the electromagnetic fields together with a generalized matrix-operator formalism. By means of a discretization of the radiation and evanescent modes, the computation of the reflection and transmission coefficients can be reduced to the numerical solution of algebraic equations. The TE-TM coupling, which takes place for oblique incidence, and the different evanescent field effects are discussed in detail. [ABSTRACT FROM AUTHOR]

Copyright of Il Nuovo Cimento: B is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The plane-wave expansion of the modified cylindrical functions, i.e., the product of the mth-order modified Bessel function K m and the angular factor exp(imϑ), is given. This expansion, which is found to involve only evanescent plane waves, may be used in the study of coupling phenomena between circular and planar guiding structures. [ABSTRACT FROM AUTHOR]

We consider the sizes of a region in a three-dimensional space in which an optical wave field excites mutually coherent perturbations. We discuss the conditions under which the length of this region along the direction of propagation of the wave field and, correspondingly, its volume are determined either by the width of the frequency spectrum of the field or by the width of its angular spectrum, or by the parameters of these spectra simultaneously. We obtain expressions for estimating extremely small values of the coherence volume of the fields with a broad frequency spectrum and an extremely broad angular spectrum. Using the notion of instantaneous speckle-modulation of the wave field, we give a physical interpretation to the occurrence of a limited coherence volume of the field. The length of the spatiotemporal coherence region in which mutually coherent perturbations occur at different times is determined. The coherence volume of a wave field that illuminates an object in high-resolution microscopy with frequency broadband light is considered. The conditions for the dominant influence of the angular or frequency spectra on the longitudinal length of the coherence region are given, and the conditions for the influence of the frequency spectrum width on the transverse coherence of the wave field are examined. We show that, when using fields with broad and ultrabroad spectra in high-resolution microscopy, this influence should be taken into account. [ABSTRACT FROM AUTHOR]

That the speed of light in vacuum is constant is a cornerstone of modern physics. However, recent experiments have shown that when the light field is confined in the transverse plane, the observed propagation speed of the light is reduced. This effect is a consequence of the transverse structure which reduces the component of wavevector of the light in the direction of propagation, thereby modifying both the phase and group velocity. Here, we consider the case of optical speckle, which has a random transverse distribution and is ubiquitous with scales ranging from the microscopic to the astronomical. We numerically investigate the plane-to-plane propagation speed of the optical speckle by using the method of angular spectrum analysis. For a general diffuser with Gaussian scattering over an angular range of 5°, we calculate the slowing of the propagation speed of the optical speckle to be on the order of 1% of the free-space speed, resulting in a significantly higher temporal delay compared to the Bessel and Laguerre–Gaussian beams considered previously. Our results have implications for studying optical speckle in both laboratory and astronomical settings. [ABSTRACT FROM AUTHOR]

Modeling is performed for an acoustic trap created in a liquid using a multi-element ring transducer operating in a megahertz frequency band. A GUI service (service with a graphical interface) is created to calculate the acoustic radiation force acting on an elastic spherical scatterer of large wave size placed in the trap. The angular spectrum is used to calculate the radiation force by solving the complete scattering problem of an acoustic beam on a spherical scatterer. Results from a numerical experiment demonstrate the possibility of retaining solid particles and allow the accuracy of this technique to be determined. [ABSTRACT FROM AUTHOR]

We consider the contribution of the stochastic component in the multipole spectrum of angular velocities of extragalactic sources. We build the complete orthonormal set of vector spherical functions, expand the vector field of angular velocities in a Fourier series in these functions, and calculate the two-point correlators of the vector spherical harmonic amplitudes and the rotationally invariant multipole coefficients. It is shown that the spectrum of multipole harmonics does not depend on the multipole number. We discuss a comparison of the theoretical predictions with experimental data. [ABSTRACT FROM AUTHOR]

Arbitrary light potentials have proven to be a valuable and versatile tool in many quantum information and quantum simulation experiments with ultracold atoms. Using a phase-modulating spatial light modulator (SLM), we generate arbitrary light potentials holographically with measured efficiencies between 15 and 40% and an accuracy of < 2 % root-mean-squared error. Key to the high accuracy is the modelling of pixel crosstalk of the SLM on a sub-pixel scale which is relevant especially for large light potentials. We employ conjugate gradient minimisation to calculate the SLM phase pattern for a given target light potential after measuring the intensity and wavefront at the SLM. Further, we use camera feedback to reduce experimental errors, we remove optical vortices and investigate the difference between the angular spectrum method and the Fourier transform to simulate the propagation of light. Using a combination of all these techniques, we achieved more accurate and efficient light potentials compared to previous studies, and generated a series of potentials relevant for cold atom experiments. [ABSTRACT FROM AUTHOR]

A method of acoustic imaging in a liquid through a solid-state lens by using phase data processing with aberration correction is proposed. Results are presented from the theoretical modeling and the experimental study of investigating objects located in water. [ABSTRACT FROM AUTHOR]

The phenomenon of acoustic radiation force acting on solid spherical scatterers inside the field of a focused ultrasonic beam is experimentally studied. Nylon and glass beads are used as scatterers; the acoustic field is generated by a piezoceramic transducer of the megahertz frequency range in water. The angular spectrum of the ultrasonic beam, obtained from the measured transverse distribution of the amplitude and phase of the acoustic pressure, is used to calculate the theoretical value of the radiation force. The results from these calculations are in agreement with the experimentally determined value of the radiation force. [ABSTRACT FROM AUTHOR]

Features of the spectral broadening of femtosecond optical vortices at self-action in a medium with the anomalous group velocity dispersion have been studied experimentally and numerically. It has been found that the broadening of the frequency–angular spectrum is accompanied by the appearance of localized maxima in the Stokes and anti-Stokes regions, which have a strip structure, near the nonlinear focus. It has been shown that in the medium with the anomalous group velocity dispersion the broadening of the spectrum in an optical vortex is smaller than that in a Gaussian beam at the same excess of the power above the critical value. [ABSTRACT FROM AUTHOR]

Direct numerical simulations of wind-generated gravity waves on a 2D sea surface are carried out within the framework of the basic potential equations of hydrodynamics. The data obtained for conditions of deep water, the JONSWAP spectrum and various wave intensities, widths of angular spectrum, and peakedness are processed and the results are discussed. The statistical and spectral characteristics of the waves evolve over a long time. The specific asymmetry of the typical profiles of anomalously high waves is shown. The durations of extreme events, which can be up to several tens of wave periods, are calculated. [ABSTRACT FROM AUTHOR]

We consider the formation of instantaneous speckle-modulated interference images of thin transparent layers in an optical microscope under their illumination of either quasi-monochromatic or frequency-broadband wave field with wide angular spectra and coherent effects that manifest themselves in this case. Using numerical modeling of spatial distributions of the complex amplitude of the wave fields reflected by the layer faces and their superposition, we have obtained instantaneous speckle-modulated interference images of the layer in the transverse and longitudinal sections of the total wave field reflected by the layer. The results of the computer modeling of instantaneous speckle-modulated and experimentally observed averaged interference images of a layer upon its illumination both with a quasi-monochromatic field and with a frequency-broadband field with different angular spectrum widths are presented. The mutual correlation of instantaneous speckle fields reflected by the faces of the layer and the effects of the width of the angular and frequency spectra of the illuminating field on the contrast of experimentally observed interference images of the layer are numerically examined. Based on the notion of instantaneous speckle modulation of the wave field, the physical mechanisms by which the width of the angular and the width of the frequency spectra of the illuminating field affect the mutual coherence of the interfering wave fields are studied. [ABSTRACT FROM AUTHOR]

A method is proposed for spatially correcting an acoustic hologram recorded on an arbitrarily oriented planar area in front of an axially symmetric ultrasound transducer. The method comprises steps for determining the direction of the transducer's axis from the measured acoustic hologram, transferring the hologram data on a plane perpendicular to this axis and centering it relative to the axis by means of a correction algorithm that executes appropriate rotations and shifts of the original hologram. The corrected hologram is used for reconstructing the structure of vibrations of the emitting surface of the transducer. A simplified correction algorithm is also considered that is applicable for transducers with narrow angular spectrum and small angles of inclination of the initial hologram to the transducer axis. The accuracy of the developed algorithms is analyzed numerically for a single focusing transducer with a uniform vibrational velocity distribution on its surface and is demonstrated experimentally for an annular 12-element array. [ABSTRACT FROM AUTHOR]

Acoustic radiation forces can remotely manipulate particles. Forces from a standing wave field align microscale particles along the nodal or anti-nodal locations of the field to form three-dimensional (3D) patterns. These patterns can be used to form 3D microstructures for tissue engineering applications. However, standing wave generation requires more than one transducer or a reflector, which is challenging to implement in vivo. Here, a method is developed and validated to manipulate microspheres using a travelling wave from a single transducer. Diffraction theory and an iterative angular spectrum approach are employed to design phase holograms to shape the acoustic field. The field replicates a standing wave and aligns polyethylene microspheres in water, which are analogous to cells in vivo, at pressure nodes. Using Gor'kov potential to calculate the radiation forces on the microspheres, axial forces are minimized, and transverse forces are maximized to create stable particle patterns. Pressure fields from the phase holograms and resulting particle aggregation patterns match predictions with a feature similarity index > 0.92, where 1 is a perfect match. The resulting radiation forces are comparable to those produced from a standing wave, which suggests opportunities for in vivo implementation of cell patterning toward tissue engineering applications. [ABSTRACT FROM AUTHOR]

A non-quadratic regularization algorithm modification is proposed. It ensures identifying and filtering angular spectrum false components by choosing regularizing functional parameters. The algorithm efficiency was proved by modeling while solving the problem of multibeam wavefield division using one input data realization. [ABSTRACT FROM AUTHOR]

The authors investigate the effect of anisotropy of the frequency-angular spectrum of wind waves on the efficiency of spatial processing signals received by a horizontal array in a shallow water waveguide with a rough surface. The array gain is analyzed for three array signal processors: conventional beamformer, optimal linear processor, and optimal quadratic processor. The numerical simulation results for the hydrological conditions typical of the Barents Sea in winter are presented. The main focus is on the dependence of the array gain on the distance to the source and wind direction with respect to the acoustic path. Simulation results for the anisotropic wind wave spectrum and a simplified model with an isotropic spectrum are also compared. [ABSTRACT FROM AUTHOR]

In the nondestructive evaluation domain, the reflection of ultrasonic waves at liquid-solid interfaces generates interesting and useful phenomena when the incident angle approaches the longitudinal critical angle or Rayleigh angle. In this paper, we have developed a model for the study of the transient ultrasonic waves radiated by a plane or a focusing transducer in a liquid and reflected by a solid plane interface. The method used is an extension of the angular spectrum method to the transient case where the reflection at the plane interface is taken into account by using the reflection coefficient for plane harmonic waves. The results obtained highlighted the different components of the ultrasonic field: the direct and edge waves as well as the longitudinal head waves or leaky Rayleigh waves. These waves have been carefully analyzed and discussed. Instantaneous cartographies allowed a clear description of all the waves which appear at the liquid-solid interface. [ABSTRACT FROM AUTHOR]

A theoretical study of dynamic ocean noise under conditions of multiple scattering of the acoustic field by anisotropic wind waves has been carried out. The influence of scattering effects on the angular and mode spectra of the noise field is discussed. The results of numerical simulation of the noise statistical characteristics for winter hydrological conditions in the Barents Sea are presented. [ABSTRACT FROM AUTHOR]

The paper describes a theoretical study of horizontal anisotropy of dynamic ocean noise. It is shown that the anisotropic distribution of the ocean noise field is governed by the effect of its scattering by wind waves. The dependence of the degree of noise anisotropy on the mode number and wind speed is discussed. [ABSTRACT FROM AUTHOR]

The focus steering capabilities of a 1 MHz linear phased array transducer (64 rectangular elements, 14.8 × 51.2 mm aperture) intended for drug delivery applications in abdominal organs were assessed and compared with its design-stage computer model. Acoustic fields generated by the transducer and predicted by the models of an ideal array with uniformly vibrating elements and either a plane or a cylindrically focused surface were simulated using the Rayleigh integral and angular spectrum methods. The boundary conditions for the transducer were reconstructed from acoustic holography measurements performed for selected focusing configurations of the array and also synthesized from holography data measured for each of its individual elements. It was shown that the transducer field with electronic focus steering can be accurately synthesized based on the holography data of its elements, which significantly simplified acoustic field characterization. Variability of the power and directivity patterns of the array elements were analyzed. A twofold smaller range of electronic steering in the transverse direction for the transducer compared to its computer model is discussed. [ABSTRACT FROM AUTHOR]

We report a generally designed optical modulation method to garner the tunable three-dimensional (3D) polarized optical multi-focal spots arrays in the focusing system of high numerical aperture (NA) objective lens, and it has good compatibility with vector beams of different polarization states. Based on the vector angular spectrum theory and Fourier transform, the vector light fields of Gaussian beam, Bessel-Gaussian (BG) beam and Laguerre-Gaussian (LG) beam are modulated with the generally designed multi-focal spots phase filter (MSPF). Meanwhile, a generally designed sidelobe suppression transmission (SST) function is employed to reduce the interference effect of the adjacent focal spots in the arrays. Thus, the one-dimensional (1D) axial multi-focal spots array and the 3D multi-focal spots arrays with high spatial resolution can be generated. The MSPF is flexible and reliable in modulating various vector beams, and exhibiting high tunability for the number (3, 12, 21), spacing (4λ–11.3λ) and spatial distribution (1D–3D) of focal spots in the array. With the generally designed MSPF, the generation of multi-focus array is promoted to be more universal and flexible and shows potential application prospects in femtosecond laser multi-beam parallel processing, particle capture, as well as high-density data storage. [ABSTRACT FROM AUTHOR]

The Modified Directional Index (MDI) is a form factor of the angular spectrum computed from the 2D Fourier transform of an image marking the prevalence of rectilinear features throughout the picture. We study some properties of the index and we apply it to AFM images of cell cytoskeleton regions featuring patterns of rectilinear nearly parallel actin filaments as in the case of microfilaments grouped in bundles. The analysis of AFM images through MDI calculation quantifies the fiber directionality changes which could be related to fiber damages. This parameter is applied to the images of Hs 578Bst cell line, non-tumoral and not immortalized human epithelial cell line, irradiated with X-rays at doses equivalent to typical radiotherapy treatment fractions. In the reported samples, we could conclude that the damages are mainly born to the membrane and not to the cytoskeleton. It could be interesting to test the parameter also using other kinds of chemical or physical agents. [ABSTRACT FROM AUTHOR]

It is shown both experimentally and theoretically that interference effects play the key role in the formation of frequency-angular spectrum of the filament conical emission. For the first time, we investigated experimentally the transformation of the conical emission frequency-angular spectrum with an increase in the filament length inside fused silica. We discovered the appearance of fine structure of the conical emission rings produced by lengthy filament. It is shown that the conical emission frequency-angular spectrum is produced by interference of coherent radiation from one or several moving point sources in the filament. The shape of the conical emission spectrum depends on the medium material dispersion, the spectrum structure is determined by length and relative location of filament emitting regions. [ABSTRACT FROM AUTHOR]

Two algorithms for the phase retrieval of hard X-ray in-line phase contrast imaging are presented. One is referred to as lterative Angular Spectrum Algorithm (IASA) and the other is a hybrid algorithm that combines IASA with TIE (transport of intensity equation). The calculations of the algorithms are based on free space propagation of the angular spectrum. The new approaches are demonstrated with numerical simulations. Comparisons with other phase retrieval algorithms are also performed. It is shown that the phase retrieval method combining the IASA and TIE is a promising technique for the application of hard X-ray phase contrast imaging. [ABSTRACT FROM AUTHOR]