Showing papers on "Bessel beam published in 2017"
TL;DR: Meta-axicons with high NA up to 0.9 capable of generating Bessel beams with full width at half maximum about as small as ~λ/3 (λ=405 nm) have transverse intensity profiles independent of wavelength across the visible spectrum.
Abstract: Bessel beams are of great interest due to their unique non-diffractive properties Using a conical prism or an objective paired with an annular aperture are two typical approaches for generating zeroth-order Bessel beams However, the former approach has a limited numerical aperture (NA), and the latter suffers from low efficiency, as most of the incident light is blocked by the aperture Furthermore, an additional phase-modulating element is needed to generate higher-order Bessel beams, which in turn adds complexity and bulkiness to the system We overcome these problems using dielectric metasurfaces to realize meta-axicons with additional functionalities not achievable with conventional means We demonstrate meta-axicons with high NA up to 09 capable of generating Bessel beams with full width at half maximum about as small as ~λ/3 (λ=405 nm) Importantly, these Bessel beams have transverse intensity profiles independent of wavelength across the visible spectrum These meta-axicons can enable advanced research and applications related to Bessel beams, such as laser fabrication, imaging and optical manipulation
186 citations
TL;DR: This paper explores the potential of orbital angular momentum multiplexing as a means to enable high-speed wireless transmission and introduces two methods to address the Rx SNR reduction issue by exploiting the property of a Gaussian beam generated by multiple uniform circular arrays and by using a dielectric lens antenna.
Abstract: This paper explores the potential of orbital angular momentum (OAM) multiplexing as a means to enable high-speed wireless transmission. OAM is a physical property of electro-magnetic waves that are characterized by a helical phase front in the propagation direction. Since the characteristic can be used to create multiple orthogonal channels, wireless transmission using OAM can enhance the wireless transmission rate. Comparisons with other wireless transmission technologies clarify that OAM multiplexing is particularly promising for point-to-point wireless transmission. We also clarify three major issues in OAM multiplexing: beam divergence, mode-dependent performance degradation, and reception (Rx) signal-to-noise-ratio (SNR) reduction. To mitigate mode-dependent performance degradation we first present a simple but practical Rx antenna design method. Exploiting the fact that there are specific location sets with phase differences of 90 or 180 degrees, the method allows each OAM mode to be received at its high SNR region. We also introduce two methods to address the Rx SNR reduction issue by exploiting the property of a Gaussian beam generated by multiple uniform circular arrays and by using a dielectric lens antenna. We confirm the feasibility of OAM multiplexing in a proof of concept experiment at 5.2 GHz. The effectiveness of the proposed Rx antenna design method is validated by computer simulations that use experimentally measured values. The two new Rx SNR enhancement methods are validated by computer simulations using wireless transmission at 60 GHz. key words: orbital angular momentum multiplexing, uniform circular array, Gaussian beam, Bessel beam, lens antenna
67 citations
TL;DR: In this article, a simple and efficient approach for multipole expansion of a circularly symmetric Bessel beam is derived, and the convergence and correctness of the beam shape coefficients are verified numerically in detail for both on-axis and off-axis cases.
64 citations
TL;DR: In this article, a high-order Bessel vortex beam carrying orbital angular momentum (OAM) is generated by using multilayer amplitude-phase-modulated surfaces (APMSs) at 10 GHz.
Abstract: A high-order Bessel vortex beam carrying orbital angular momentum (OAM) is generated by using multilayer amplitude-phase-modulated surfaces (APMSs) at 10 GHz. The APMS transmitarray is composed of four-layer conformal square-loop (FCSL) surfaces with both amplitude and phase modulation. The APMS can transform a quasi-spherical wave emitted from the feeding source into a pseudo non-diffractive high-order Bessel vortex beam with OAM. The APMS for a second-order Bessel beam carrying OAM in the n = 2 mode is designed, fabricated, and measured. Full-wave simulation and measurement results confirm that Bessel vortex beams with OAM can be effectively generated using the proposed APMS transmitarray.
61 citations
TL;DR: It is demonstrated that the tailored fs Bessel beam can be used to fabricate a 2D array of approximately ∅10- μm TSVs on a 100-μm-thick Si substrate without any sidelobe damage, suggesting potential application in the 3D assembly of 3D Si ICs.
Abstract: Three-dimensional integrated circuits (3D ICs) are an attractive replacement for conventional 2D ICs as high-performance, low-power-consumption, and small-footprint microelectronic devices. However, one of the major remaining challenges is the manufacture of high-aspect-ratio through-silicon vias (TSVs), which is a crucial technology for the assembly of 3D Si ICs. Here, we present the fabrication of high-quality TSVs using a femtosecond (fs) 1.5-μm Bessel beam. To eliminate the severe ablation caused by the sidelobes of a conventional Bessel beam, a fs Bessel beam is tailored using a specially designed binary phase plate. We demonstrate that the tailored fs Bessel beam can be used to fabricate a 2D array of approximately ∅10-μm TSVs on a 100-μm-thick Si substrate without any sidelobe damage, suggesting potential application in the 3D assembly of 3D Si ICs.
56 citations
TL;DR: A gradient acoustic metasurface to manipulate acoustic wavefront freely and some excellent wavefront manipulations are demonstrated by anomalous refraction, non-diffracting Bessel beam, sub-wavelength flat focusing, and effective tunable acoustic negative refraction.
Abstract: We designed a gradient acoustic metasurface to manipulate acoustic wavefront freely. The broad bandwidth and high efficiency transmission are achieved by the acoustic metasurface which is constructed with a series of unit cells to provide desired discrete acoustic velocity distribution. Each unit cell is composed of a decorated metal plate with four periodically arrayed Helmholtz resonators (HRs) and a single slit. The design employs a gradient velocity to redirect refracted wave and the impedance matching between the metasurface and the background medium can be realized by adjusting the slit width of unit cell. The theoretical and numerical results show that some excellent wavefront manipulations are demonstrated by anomalous refraction, non-diffracting Bessel beam, sub-wavelength flat focusing, and effective tunable acoustic negative refraction. Our designed structure may offer potential applications for the imaging system, beam steering and acoustic lens.
48 citations
TL;DR: In this Letter, superposed SBBs are realized by alternatively imprinting holograms of opposite-order Bessel beams along the radial direction on a spatial light modulator, and the propagation invariance and non-rotation properties are theoretically predicted and experimentally demonstrated.
Abstract: In this Letter, superposed Bessel beams (SBBs) are realized by alternatively imprinting holograms of opposite-order Bessel beams along the radial direction on a spatial light modulator. The propagation invariance and non-rotation properties of SBBs are theoretically predicted and experimentally demonstrated. The focusing property of SBBs with a high numerical aperture (NA) objective is investigated with the Debye vectorial diffraction theory. Near the focal plane, a circularly distributed multiple foci pattern is achieved. The multiple foci generated from SBBs are adopted in a two-photon fabrication system, and micropattern fabrication by a single exposure is demonstrated. Facile fabrication of three-dimensional microstructures with SBBs is realized by dynamically controlling the number of focal spots, and the diameter and rotation of the focal pattern.
44 citations
TL;DR: In this article, it was shown that a higher order Bessel beam with azimuthal phase variation can be generated in the near field by synthesizing an inward cylindrical traveling-wave distribution over a finite aperture antenna.
Abstract: In this communication, it is shown that a nondiffracting vortex beam (i.e., a higher order Bessel beam with azimuthal phase variation) can be generated in the near field by synthesizing an inward cylindrical traveling-wave distribution over a finite aperture antenna. A radial line slot array (RLSA) is then designed to prove the concept. The collimated vortex beam is excited in the proximity of the RLSA, within a region properly defined by the nondiffracting range of the generated beam. The radial dependence of the longitudinal electric field of the vortex-beam magnitude follows a first-order Bessel function, and its phase presents a linear azimuthal variation. Full-wave results validate the generation of the nondiffractive higher order Bessel beam within the radiative near field of the launcher.
43 citations
TL;DR: A wideband phase shift surface (PSS) antenna is proposed in this article, which launches quasi-nondiffraction beam with accurately controllable inclination angle and depth-of-field.
Abstract: A wideband phase shift surface (PSS) antenna is proposed in this paper, which launches quasi-nondiffraction beam with accurately controllable inclination angle and depth-of-field. First, a novel method to generate the off-axis quasi-nondiffraction beam in an arbitrary direction is proposed. It modifies and further combines the design methods of the off-axis focusing antenna and the zero-order Bessel beam antenna. This method is helpful to improve the design precision of the depth-of-field of the beam. Then, one kind of hexagonal patch is employed as the element of the PSS. Its phase shift compensation capability can increase the bandwidth and improve the stability of the performance of the antenna over a wideband from 27 to 31 GHz. The results of numerical simulation, full-wave simulation, and experiment show that the proposed antenna can effectively generate the expected beam.
41 citations
TL;DR: In this article, a miniature evanescent Bessel beam generator is realized by utilizing the combination of metasurfaces based on a concentric grating and hyperbolic metamaterials composed of alternate metal/dielectric multilayers.
Abstract: A miniature evanescent Bessel beam generator is realized by utilizing the combination of metasurfaces based on a concentric grating and hyperbolic metamaterials composed of alternate metal/dielectric multilayers. After introducing the plasmonic cavity lens, the feature size could be compressed to 62 nm (0.17λ0) at the wavelength of 365 nm with a working distance as large as 100 nm. The theoretical models are verified by a set of experiments, providing a promising way to control light at the nanoscale.
40 citations
TL;DR: In this article, a general description of transverse mode Bessel beams is proposed based on an analysis of polarized Bessel beam using the Hertz vector potentials and the angular spectrum representation (ASR).
Abstract: Based on an analysis of polarized Bessel beams using the Hertz vector potentials and the angular spectrum representation (ASR), a general description of transverse mode Bessel beams is proposed. As opposed to the cases of linearly and circularly polarized Bessel beams, the magnetic and electric fields of a Bessel beam in a transverse mode are orthogonal to each other. Both sets of fields together form a complete set of basis Bessel fields, in terms of which an arbitrary Bessel beam can be regarded as a linear combination. The completeness of the basis Bessel fields is analyzed from the perspectives of waveguide theory and vector wave functions. Decompositions of linearly polarized, circularly polarized, and circularly symmetric n -order Bessel beams in terms of basis Bessel fields are given. The results presented in this paper provide a fresh perspective on the description of Bessel beams, which are useful in casting insights into the experimental generation of Bessel beams and the interpretation of light scattering-related problems in practice.
TL;DR: In this paper, the authors realize low-dimensional tight-binding lattices that host flat bands in their dispersion relation and demonstrate the existence of optical compact flat band states, similar to arrays of optical waveguides fabricated by the spatio-temporal Bessel beam multiplexing optical induction in photorefractive media.
Abstract: We realize low-dimensional tight-binding lattices that host flat bands in their dispersion relation and demonstrate the existence of optical compact flat band states. The lattices are resembled by arrays of optical waveguides fabricated by the state-of-the-art spatio-temporal Bessel beam multiplexing optical induction in photorefractive media. We work out the decisive details of the transition from the discrete theory to the real optical system ensuring that the experimental lattices stand up to numerical scrutiny exhibiting well-approximated band structures. Our highly flexible system is a promising candidate for further experimental investigation of theoretically studied disorder effects in flat band lattices.
TL;DR: In this article, the beam shape coefficients of on-axis zeroth-order Bessel beams are evaluated using localized approximation procedures for small axicon angles, and it is shown that these procedures are valid only for small Bessel angles.
Abstract: Localized approximation procedures are efficient ways to evaluate beam shape coefficients of laser beams, and are particularly useful when other methods are ineffective or inefficient. Several papers in the literature have reported the use of such procedures to evaluate the beam shape coefficients of Bessel beams. Examining the specific case of an on-axis zeroth-order Bessel beam, we demonstrate that localized approximation procedures are valid only for small axicon angles.
TL;DR: In this article, the authors demonstrated the creation of a narrow, straight flow in air to a distance of 400mm from an ultrasound phased array emitting a Bessel beam, which can be controlled by appropriately tuning the wavefronts of the emission from the phased array.
Abstract: Acoustic streaming, which is the unidirectional movement of a medium driven by its internal intense acoustic vibrations, has been known for more than a century. Despite the long history of research, there have been no scientific reports on the creation of long stretching steerable airflows in an open space, generated by ultrasound. Here, we demonstrated the creation of a narrow, straight flow in air to a distance of 400 mm from an ultrasound phased array emitting a Bessel beam. We also demonstrated that the direction of the flow could be controlled by appropriately tuning the wavefronts of the emission from the phased array. Unlike conventional airflows such as those generated by jets or fans, which decelerate and spread out as they travel farther, the flow that we created proceeded while being accelerated by the kinetic energy supplied from the ultrasound beam and keeping the diameter as small as the wavelength. A flow of 3 m/s with a 10 mm diameter extended for several hundreds of millimeters in a room ...
TL;DR: In this Letter, continuous Bessel theory is manipulated to formulate the phase and amplitude conditions necessary for generating free-space-propagating Bessel-Gauss beams using on-chip optical phased arrays.
Abstract: Integrated optical phased arrays for generating quasi-Bessel beams are proposed and experimentally demonstrated in a CMOS-compatible platform. Owing to their elongated central beams, Bessel beams have applications in a range of fields, including multiparticle trapping and laser lithography. In this Letter, continuous Bessel theory is manipulated to formulate the phase and amplitude conditions necessary for generating free-space-propagating Bessel–Gauss beams using on-chip optical phased arrays. Discussion of the effects of select phased array parameters on the generated beam’s figures of merit is included. A one-dimensional splitter-tree-based phased array architecture is modified to enable arbitrary passive control of the array’s element phase and amplitude distributions. This architecture is used to experimentally demonstrate on-chip quasi-Bessel-beam generation with a ∼14 mm Bessel length and ∼30 μm power full width at half maximum.
TL;DR: An effective microoperating system for single cell manipulation using microtube arrays is constructed, and its use in the capture, transfer, and release of embryonic fibroblast mouse cells as well as human breast cancer cells is demonstrated.
Abstract: In this paper, we present a focused femtosecond laser Bessel beam scanning technique for the rapid fabrication of large-area 3D complex microtube arrays. The femtosecond laser beam is converted into several Bessel beams by two-dimensional phase modulation using a spatial light modulator. By scanning the focused Bessel beam along a designed route, microtubes with variable size and flexible geometry are rapidly fabricated by two-photon polymerization. The fabrication time is reduced by two orders of magnitude in comparison with conventional point-to-point scanning. Moreover, we construct an effective microoperating system for single cell manipulation using microtube arrays, and demonstrate its use in the capture, transfer, and release of embryonic fibroblast mouse cells as well as human breast cancer cells. The new fabrication strategy provides a novel method for the rapid fabrication of functional devices using a flexibly tailored laser beam.
TL;DR: The analysis using the partial‐wave series expansion (PWSE) method in spherical coordinates is extended to evaluate the acoustic radiation force experienced by rigid oblate and prolate spheroids centered on the axis of wave propagation of high‐order Bessel vortex beams composed of progressive, standing and quasi‐standing waves.
TL;DR: In this article, it was shown that the incident wave field can act as a tractor beam in the dipole approximation (Rayleigh) limit, provided that the particle is made of an active material, i.e., a dielectric spheroid acting as an oscillating source for which the extinction energy efficiency is negative.
Abstract: Optical Bessel tractor beams, designed to produce a negative pulling force on a particle, are gaining increased attention for applications in noncontact remote sampling, particle manipulation, and handling, to name some examples. In the long-wavelength (Rayleigh) limit, known also as the electric dipole approximation, earlier investigations demonstrated that a zeroth-order Bessel beam incident upon a passive dielectric sphere (i.e., no radiating sources in its core) always acts as a repulsor beam, which causes the particle to be pushed away from the source in the forward direction of the linear momentum. In contrast to what has already been established, this work shows that the incident wave field can act as a tractor beam (where a small spheroid is pulled backwards towards the source due to a negative attractive force) in the dipole approximation (Rayleigh) limit, provided that the particle is made of an active material, i.e., a dielectric spheroid acting as an oscillating source for which the extinction energy efficiency is negative. Numerical computations for the Cartesian components of the optical radiation force on active prolate and oblate spheroids with arbitrary orientation are performed. Emphasis is placed on the emergence of the tractor beam behavior and its dependence upon the half-cone angle, the polarization type of the incident beam, the spheroid aspect ratio, as well as its orientation in space. The analysis is extended to calculate the Cartesian components of the spin radiation torque, which causes a rotation of the spheroid around its center of mass in either the counterclockwise or the clockwise (negative) direction of spinning. Unlike the case of a sphere, the optical spin torque arises for a nonabsorptive oblate or prolate spheroid with arbitrary orientation in the field of a zeroth-order Bessel beam. Potential applications in optically engineered metamaterials, optical tractor beams, tweezers, particle manipulation, rotation, and handling would benefit from the results of this study.
TL;DR: In this article, the authors compare the quality of cleaving in glass samples obtained using Bessel beams with both circularly symmetric and elliptical transverse profiles, and find that the use of an elliptical Bessel beam generates elliptical nanochannels, which greatly improves the cleavage quality and cuts material strength.
Abstract: The material processing technique of “stealth” nanomachining is based on translating a longitudinally extended beam such as a Bessel beam into a transparent sample to generate extended nanochannels, which leads to subsequent internal stress that facilitates high quality cleaving. In this letter, we compare the quality of such cleaving in glass samples obtained using Bessel beams with both circularly symmetric and elliptical transverse profiles. We find that the use of an elliptical Bessel beam generates elliptical nanochannels, which greatly improves the cleavage quality and cuts material strength by aligning the centre of the cleavage plane with the centre of the machined channels. These results are interpreted using numerical simulations that show how elliptical nanochannels enhance the intensity and localization of the tensile stress distribution in glass under bending when compared to channels with circular cross-sections.
20 Sep 2017
TL;DR: In this article, the authors used two self-reconstructing Bessel beams in continuous wave mode with a different angular momentum for fluorescence excitation and depletion along a distance of 110μm.
Abstract: Stimulated emission depletion (STED) microscopy generates super-resolved images of single cells by point-wise depletion of fluorescence around a small focal volume. Scanned light sheet microscopy, on the other side, generates images line-wise by scanning a weakly focused laser beam through thousands of scattering cells. Here we address the question of whether fluorescence from an excitation beam can be depleted by a STED beam over tens of micrometers while propagating through scattering material. Therefore, we use two self-reconstructing Bessel beams in continuous wave mode with a different angular momentum for fluorescence excitation and depletion along a distance of 110 μm. We show that despite significant scattering at various arrangements of microspheres embedded in agarose gel and despite strong losses in spatial coherence, it is possible to generate a sufficiently good overlap of both beam intensities. Without affecting the self-healing capability of the illumination photons in the Bessel beam’s ring system, the emission of fluorescence photons thereof can be strongly suppressed. This results in a needle-like fluorescence distribution inside scattering media, providing new perspectives for fundamental principles and applications in microscopy and metrology.
TL;DR: Two planar Bessel beam launchers are designed at millimeter waves with a center operating frequency of f¯=60GHz and analyzed in the bandwidth 50 - 70 GHz by using an in-house developed numerical code to solve Maxwell's equations based on the method of moments.
Abstract: In this paper, a comparison is presented between Bessel beam launchers at millimeter waves based on either a cylindrical standing wave (CSW) or a cylindrical inward traveling wave (CITW) aperture distribution. It is theoretically shown that CITW launchers are better suited for the generation of electromagnetic short pulses because they maintain their performances over a larger bandwidth than those realizing a CSW aperture distribution. Moreover, the wavenumber dispersion of both the launchers is evaluated both theoretically and numerically. To this end, two planar Bessel beam launchers, one enforcing a CSW and the other enforcing a CITW aperture distribution, are designed at millimeter waves with a center operating frequency of f¯=60GHz and analyzed in the bandwidth 50 - 70 GHz by using an in-house developed numerical code to solve Maxwell's equations based on the method of moments. It is shown that a monochromatic Bessel beam can be efficiently generated by both the launchers over a wide fractional bandwidth. Finally, we investigate the generation of limited-diffractive electromagnetic pulses at millimeter waves, up to a certain non-diffractive range. Namely, it is shown that by feeding the launcher with a Gaussian short pulse, a spatially confined electromagnetic pulse can be efficiently generated in front of the launcher.
TL;DR: It is shown that 360° laser illumination in combination with a radial polarizer will generate an evanescent Bessel-beam excitation field that exhibits a flattop intensity over an extended part of the field of view, and the advantages of this axicon-based Bessel beam illumination for live-cell imaging.
Abstract: Total internal reflection fluorescence microscopy (TIRF-M) provides low-invasive high-contrast surface imaging with optical sectioning of typically 100–200 nm. Thus, TIRF-M has become an established tool for imaging surfaces, including cell membranes. For TIRF-M, a homogenous evanescent field of excitation over the whole field of view is generally desired for quantitative microscopy; however, this is not necessarily straightforward to generate with Gaussian beams. In recent years, several improvements on TIRF-M have been developed that have addressed non-uniform scattering fringes and other artifacts. Here, we introduce a cost-effective TIRF setup with a very low degree of complexity and no moving parts, which provides a flattop-like excitation profile. The setup uses a tunable laser ring zoom focus system to generate a full 360° TIRF illumination. Two axicon lenses and one focus lens allow for generation and control of the ring diameter to tune the TIRF excitation angle. We show that 360° laser illumination in combination with a radial polarizer will generate an evanescent Bessel-beam excitation field that exhibits a flattop intensity over an extended part of the field of view, and demonstrate the advantages of this axicon-based Bessel beam illumination for live-cell imaging.
TL;DR: In this article, a deep seated negative axicon (DSNA) with micrometer dimensions inside a selective optical fiber tip for the generation of optical Bessel beams (BBs) is demonstrated.
Abstract: In this letter, we have demonstrated the fabrication of a deep seated negative axicon (DSNA) with micrometer dimensions inside a selective optical fiber tip for the generation of optical Bessel beams (BBs). The DSNA is prepared by simple chemical etching of the fiber tip in hydrofluoric acid under the influence of capillary action. The selective optical fiber has a high numerical aperture of 0.3 and a small core diameter of about $4~\mu \text{m}$ . The higher etching rate of the optical fiber core contributes to fabricate the DSNA, which converts Gaussian-like beam into BB. The central spot of the BB shows quasi-invariant spot-size over the propagation distance of sub-millimeter and centimeter range. The self-protected DSNA can be useful for scanning optical fiber endoscopy applications as well as can be integrated into systems, where non-diffracting BB is preferred.
TL;DR: This investigation provides unique way to guide the in-plane transport of SPPs by using dielectric subwavelength elements, which may achieve potential applications in plasmonic integrated circuits.
Abstract: In this work, we present in-plane propagation of surface plasmon polaritons (SPPs) guided by a single dielectric (Al2O3) subwavelength lens. By mounting a designed Al2O3 nanoparticle on the silver film, the effective index of a silver-Al2O3 interface is influenced by the particle thickness, then the phase difference between the silver-air and silver-Al2O3 interface can be utilized to modulate the in-plane propagation of SPPs. We show that an elliptical Al2O3 lens transforms the diffusive SPPs into a collimated beam, whose direction of propagation and beam width can be easily controlled. We also present that a triangular Al2O3 lens significantly reforms the SPPs to a Bessel beam, which possesses non-diffractive and self-healing properties. Our investigation provides unique way to guide the in-plane transport of SPPs by using dielectric subwavelength elements, which may achieve potential applications in plasmonic integrated circuits.
TL;DR: In this article, a higher-order Bessel beam is generated by enforcing an inward cylindrical traveling-wave distribution over a finite aperture, showing the promising possibility to carry orbital angular momentum through highly focused X-shaped pulses up to the nondiffractive range.
Abstract: We discuss the generation and propagation of nondiffracting twisted pulses at microwaves, obtained through polychromatic spectral superposition of higher-order Bessel beams. The inherent vectorial structure of Maxwell's equations has been considered to generalize the nondiffracting solution of the scalar wave equation with azimuthal phase variation. Since a wide frequency bandwidth is necessary to synthesize time-limited pulses, the non-negligible wavenumber frequency dispersion, which commonly affects the propagation in the microwave range, has been taken into account. For this purpose, a higher-order Bessel beam is generated by enforcing an inward cylindrical traveling-wave distribution over a finite aperture. We present and discuss the main aspects of the generation of twisted pulses in the microwave range, showing the promising possibility to carry orbital angular momentum through highly focused X-shaped pulses up to the nondiffractive range.
TL;DR: In this article, the T-matrix (null-field) method is developed to investigate the acoustic scattering by a rigid fixed (immovable) finite cylinder with two spheroidal endcaps immersed in a non-viscous fluid under the illumination of an unbounded zeroth-order Bessel beam with arbitrary orientation.
TL;DR: In this article, a space folding acoustic metasurface with a V-shaped structure is proposed to steer refracted wavefronts at will, including anomalous refraction, non-diffracting Bessel beam, sub-wavelength flat lens, and conversion of the propagating wave into the surface wave.
Abstract: We present a space folding acoustic metasurface with a V-shaped structure, which exhibits ultra-broadband and high efficiency transmission compared to previously investigated space folding metasurfaces. The proposal employs a gradient refractive index profile to redirect the refracted wave arbitrarily and an existence of air channels with direct sound propagation to improve impedance matching between the metasurface and the background medium. As expected from frequency-independent generalized Snell's law, the demonstrated acoustic metasurface can steer refracted wavefronts at will, including anomalous refraction, non-diffracting Bessel beam, sub-wavelength flat lens, and conversion of the propagating wave into the surface wave. The designed V-shape metasurface overcomes the limitation of narrowband, which may offer potential applications in medical ultrasound imaging and broadband acoustical devices.
TL;DR: It is shown that naturally occurring magnetic vortices with circular magnetic moment distributions in a soft-magnetic thin film create conical phase shifts for fast electrons to generate efficient nondiffracting electron Bessel beams.
Abstract: We demonstrate experimentally an efficient electron axicon lens using a magnetic vortex. We show that naturally occurring magnetic vortices with circular magnetic moment distributions in a soft-magnetic thin film create conical phase shifts for fast electrons. Such radially symmetric linear phase ramps are equivalent to ideal light optical axicons. We apply this lens to generate efficient nondiffracting electron Bessel beams, which we observe experimentally in through-focus Lorentz images as well as in propagated off-axis electron holograms. This highlights the potential for using magnetic nanostructures as highly efficient and flexible phase plates for crafting desired electron beam shapes.
TL;DR: In this article, the effect of turbulent atmosphere on a generalized spiraling Bessel beam (GSBB) created by illuminating a curved fork-shaped hologram with a Laguerre-Gaussian beam was studied.
Abstract: In this paper, we study the effect of turbulent atmosphere for a new type of Bessel-like beams family by considering a generalized spiraling Bessel beam (GSBB) created by illuminating a curved fork-shaped hologram with a Laguerre–Gaussian beam. Based on the extended Huygens–Fresnel integral formula in the paraxial approximation, by means of the Rytov method and using the expression of the hard aperture function into a finite sum of complex Gaussian functions, an analytical expression of the on-axis average intensity for the considered beams family is derived. Some numerical simulations for the GSBB propagating in atmospheric turbulence are given and discussed by studying the influences of some factors as the beam topological charge, the beam waist, the wavelength and the turbulent strength.
21 Aug 2017
TL;DR: In this article, the optical radiation force, spin and orbital torques on a subwavelength prolate gold spheroid coated by a layer of plasmonic material with negative permittivity and illuminated by either a zeroth-order (non-vortex) or a first-order vector Bessel (vortex), beam are computed in the framework of the electric dipole approximation method.
Abstract: The optical radiation force, spin and orbital torques exerted on a subwavelength prolate gold spheroid coated by a layer of plasmonic material with negative permittivity and illuminated by either a zeroth-order (non-vortex) or a first-order vector Bessel (vortex) beam are computed in the framework of the electric dipole approximation method. Calculations for the Cartesian components of the optical radiation force on a subwavelength spheroid with arbitrary orientation in space are performed, with emphasis on the order (or topological charge), half-cone angle of the beam, and the plasmonic layer thickness on- and off-resonance. A repulsive (pushing) force is predicted for the layered subwavelength prolate spheroid, on- and off-resonance along the direction of wave propagation. Moreover, the Cartesian components of the spin radiation torque are computed where a negative longitudinal spin torque component can arise, suggesting a rotational twist of the spheroid around its center of mass in either the counter-clockwise or the clockwise (negative) direction of spinning. In addition, the longitudinal component of the orbital radiation torque exhibits sign reversal, indicating a revolution around the beam axis in either the counter-clockwise or the clockwise directions. The results show that the plasmonic resonance strongly alters the force, spin and orbital torque components, causing major amplitude enhancements, signs twists, and complex distributions in the transverse plane.