Showing papers on "Bessel beam published in 2021"
TL;DR: In this paper, four different and special approaches for creating nondiffracting beams in axicons are compared: Diffractive axicons, meta-axicons-flat optics, spatial light modulators, and photonic integrated circuit-based axicons.
Abstract: Axicon is a versatile optical element for forming a zero-order Bessel beam, including high-power laser radiation schemes. Nevertheless, it has drawbacks such as the produced beam’s parameters being dependent on a particular element, the output beam’s intensity distribution being dependent on the quality of element manufacturing, and uneven axial intensity distribution. To address these issues, extensive research has been undertaken to develop nondiffracting beams using a variety of advanced techniques. We looked at four different and special approaches for creating nondiffracting beams in this article. Diffractive axicons, meta-axicons-flat optics, spatial light modulators, and photonic integrated circuit-based axicons are among these approaches. Lately, there has been noteworthy curiosity in reducing the thickness and weight of axicons by exploiting diffraction. Meta-axicons, which are ultrathin flat optical elements made up of metasurfaces built up of arrays of subwavelength optical antennas, are one way to address such needs. In addition, when compared to their traditional refractive and diffractive equivalents, meta-axicons have a number of distinguishing advantages, including aberration correction, active tunability, and semi-transparency. This paper is not intended to be a critique of any method. We have outlined the most recent advancements in this field and let readers determine which approach best meets their needs based on the ease of fabrication and utilization. Moreover, one section is devoted to applications of axicons utilized as sensors of optical properties of devices and elements as well as singular beams states and wavefront features.
30 citations
TL;DR: In this article, a terahertz (THz) DDL combining the functionalities of three conventional bulky refractive hyperbolic, spiral phase plane, and aixcon lenses is proposed to generate nondiffractive Bessel vortex beam carrying OAM.
Abstract: Conventional vortex beams carrying orbital angular momentum (OAM) suffer from the limitation of beam divergence in wireless communications applications. This article proposes novel 3-dimensional (3-D) printed discrete dielectric lenses (DDLs) for generation of nondiffractive OAM beams operating at 300 GHz. By virtue of its arbitrary aperture phase control capability, a terahertz (THz) DDL combining the functionalities of three conventional bulky refractive hyperbolic, spiral phase plane, and aixcon lenses is proposed to generate nondiffractive Bessel vortex beam carrying OAM. An aperture field analysis method is also developed to evaluate the radiation performance of the DDL antennas. Furthermore, to cover the OAM signal in an intended longitudinal region, two DDL synthesis methods are explored to generate extended higher order Bessel beams carrying OAM. The first approach is based on geometric optics, while the second uses the alternating projection method (APM) to optimize the aperture phase distribution of the DDL. Two THz DDLs are conveniently fabricated by 3-D printing technology. Measured results demonstrate that THz nondiffractive OAM beams can be successfully generated by the designed DDLs. The generated THz OAM beam with attractive nondiffractive characteristic may open new opportunities for next-generation ultra-high-speed wireless communications.
27 citations
TL;DR: In this article, a two-photon light-sheet microscopy with an extended Bessel beam for a tunable field of view and reduced photodamage is presented.
Abstract: Two-photon excitation can lower phototoxicity and improve penetration depth, but its narrow excitation range restricts its applications in light-sheet microscopy. Here, we propose simple illumination optics, a lens-axicon triplet composed of an axicon and two convex lenses, to generate longer extent Bessel beams. This unit can stretch the beam full width at half maximum of 600–1000 μm with less than a 4-μm waist when using a 10× illumination lens. A two-photon excitation digital scanned light-sheet microscope possessing this range of field of view and ~2–3-μm axial resolution is constructed and used to analyze the cellular dynamics over the whole body of medaka fish. We demonstrate long-term time-lapse observations over several days and high-speed recording with ~3 mm3 volume per 4 s of the embryos. Our system is minimal and suppresses laser power loss, which can broaden applications of two-photon excitation in light-sheet microscopy. Here, the authors present a two-photon light-sheet microscopy with an extended Bessel beam for a tunable field of view and reduced photodamage. They demonstrate long-term imaging of cellular dynamics over the whole body of medaka fish.
25 citations
TL;DR: In this article, the authors proposed a method to generate and allow conversion from any orthogonal polarizations to independent Bessel beams with a single-layer dielectric metasurface.
Abstract: A Bessel beam has the properties of propagation invariance and a self-healing effect, leading to a variety of interesting phenomena and applications. Recently, as a planar diffractive element with miniaturized size, metasurfaces are widely employed to manipulate light in the subwavelength region, including generating a Bessel beam. However, such a metasurface-generated Bessel beam allows output light with no tunable functions. Here, with the interplay of the geometric phase and the dynamic phase, we propose a method to generate and allow conversion from any orthogonal polarizations to independent Bessel beams with a single-layer dielectric metasurface. The simulation results indicate that the arbitrary conversion between different Bessel beams is related to the spin-dependent orbit motion caused by the tight-focusing effect, leading to the singularity of the spot. This physical mechanism is well studied and the theoretical model for revealing the dependence of different incident polarization on the conversion dynamics is presented. Our approach paves a way for efficient generation and multifunctional applications, ranging from high-numerical-aperture devices to compact nanophotonic platforms for spin-dependent structured beams.
22 citations
TL;DR: In this paper, a single pass cutting of glass substrates with a curved edge is demonstrated using ultrafast curving Bessel and Airy beams, and the advantages of each beam are considered.
Abstract: Single-pass cutting of glass substrates with a curved edge is demonstrated using ultrafast curving Bessel and Airy beams, and the advantages of each beam are considered. To achieve successful cutting using the curving Bessel beam, crack directionality is controlled to be perpendicular to the cut by modifying the beam’s spectrum, and a flat-top intensity profile is used to increase consistency. When cutting using Airy beams, a modified beam called an oblong Airy beam is used, which has an oblong focal-spot shape, flat-top intensity profile, and increased contrast between the focal spot and sidelobes as compared to a Gaussian Airy beam. In both cases, the beams’ phase profiles are chosen to maximize edge curvature for a specific sample thickness. Cutting of 500 μm thick glasses in a single laser pass with a high (>10 μm) pitch between laser shots is demonstrated.
16 citations
TL;DR: In this paper, the existence of newly additional axicon forces associated to both the usual scattering and gradient forces was demonstrated when a Rayleigh particle is illuminated by an off-axis Bessel beam.
Abstract: In two recent papers, it has been demonstrated that, beside usual scattering and optical forces, new optical forces and terms are exhibited when a Rayleigh particle is illuminated by an off-axis Bessel beam. Namely, (i) axicon optical forces are associated with scattering optical forces and (ii) additional axicon terms are associated with gradient optical forces. These extra-axicon forces and terms are zero when the axicon angle is zero and/or (most often) when an on-axis configuration is considered rather than an off-axis configuration. This study was devoted to longitudinal forces. The present paper is devoted to transverse forces and demonstrates the existence of newly additional axicon forces associated to both the usual scattering and gradient forces. Again, these new extra-axicon forces are zero when the axicon angle is zero and/or when an on-axis configuration is considered rather than an off-axis configuration.
16 citations
TL;DR: In this paper, the authors presented a theoretical analysis, design, and fabrication of a limited-diffractive planar Bessel beam launcher, that exhibits a zeroth-order Bessel profile in the transverse electric field component with respect to the propagation axis.
Abstract: In this communication, we present a theoretical analysis, design, and fabrication of a limited-diffractive planar Bessel beam launcher, that exhibits a zeroth-order Bessel profile in the transverse electric field component with respect to the ${z}$ -propagation axis. The launcher is designed by synthesizing a finite zeroth-order, first kind Hankel aperture distribution, polarized along a fixed polarization unit vector. The field radiated by such an aperture distribution is derived by following an approximate model based on the geometric theory of diffraction, thus allowing to highlight the relevant wave constituents involved in transverse Bessel beam generation, also including the effect of aperture truncation on the radiated beam. Moreover, the theoretical analysis has been profitably applied to the design of a circular-polarized planar transverse Bessel beam launcher by means of a slotted radial waveguide. A prototype of right-handed circular polarized (RHCP) transverse Bessel beam launcher has then been fabricated at $f = 30$ GHz. The measured transverse electric field component shows a satisfactory agreement with full-wave numerical simulations.
16 citations
TL;DR: In this paper, the scattering of a nondiffractive Bessel beam (BB) incident field by a perfect electric conducting circular cylinder is investigated and compared with the standard scattering solution by a plane wave.
Abstract: In this letter, the scattering of a nondiffractive Bessel beam (BB) incident field by a perfect electric conducting circular cylinder is investigated and compared with the standard scattering solution by a plane wave It is proven that the BB incident field improves the validity of standard physical optics approximation and possibly extends its range of applicability to cylinders, or more general scatterers, whose curvature radius is not much larger than the operating wavelength This offers new effective possibilities in the solutions of different electromagnetic scattering problems
13 citations
TL;DR: An analytic and closed-form formula for the asymmetry factor, which ultimately determines the sense of direction of photophoretic force, is provided and can be applied to a wider class of axisymmetric beams carrying nonzero topological charges.
Abstract: Compared to the experimental progresses made in the optical trapping of aerosol particles in gaseous media by means of photophoretic forces, the theoretical analysis of photophoretic forces is less developed, the underlying mechanisms being yet not fully understood. In this paper, theoretical derivations of photopheresis of a dielectric sphere in gaseous media illuminated by a circularly symmetric Bessel beam of arbitrary order is presented within the framework of generalized Lorenz-Mie theory. An analytic and closed-form formula for the asymmetry factor, which ultimately determines the sense of direction of photophoretic force, is provided. The influences of particle size, absorptivity of the particle, half-cone angle, beam order of the Bessel beam on the asymmetry factor are explored in detail. The method proposed in this paper can be applied to a wider class of axisymmetric beams carrying nonzero topological charges.
12 citations
TL;DR: In this article, quasi-ring Airy vortex beams (QRAVBs) were successfully generated in the experiments to increase the received power under the limited-size receiving aperture conditions, by employing 72-Gbit/s 16-ary quadrature amplitude modulation (16-QAM) discrete multi-tone (DMT) signals.
Abstract: Vortex beams carrying orbital angular momentum (OAM), which feature helical wavefronts, have been regarded as an alternative degree of freedom for free-space optical (FSO) communication systems. However, in practical applications, atmospheric turbulence and limited-size receiving aperture effects will cause OAM modal degradation and seriously reduce the received power. In this paper, by controlling the radial phase distribution of conventional OAM beams, quasi-ring Airy vortex beams (QRAVBs) are successfully generated in the experiments to increase the received power under the limited-size receiving aperture conditions. By employing 72-Gbit/s 16-ary quadrature amplitude modulation (16-QAM) discrete multi-tone (DMT) signals, we successfully demonstrate free-space data transmission with QRAVBs in the experiments. Moreover, the transmission performance of QRAVBs under atmospheric turbulence is also evaluated. Comparing with conventional OAM beam and Bessel beam, the obtained results show that QRAVBs can achieve higher received power and better BER performance under limited-size receiving aperture and atmospheric turbulence conditions.
12 citations
TL;DR: In this paper, Bessel beam femtosecond laser micromachining was used for drilling high aspect ratio microholes with minor thermal impact. And the experimental results show that the depth of microhole is increasing with the pulse number accumulating for low energy laser pulses.
TL;DR: Corrections to the beam such as shortening, moving the intensity of the beam within the substrate, and the formation of an elliptical focal spot were necessary to ensure consistent chamfering of the substrate and are discussed herein.
Abstract: Ultrafast laser cutting of a glass substrate at an oblique angle is demonstrated using a phase-corrected Bessel beam. Simulations are used to predetermine the ideal phase of the incident Bessel beam such that an unaberrated Bessel beam is formed inside the tilted substrate. Additional corrections to the beam such as shortening, moving the intensity of the beam within the substrate, and the formation of an elliptical focal spot were necessary to ensure consistent chamfering of the substrate and are discussed herein. Three cuts are combined to create a damage tract in the glass substrate in the shape of a chamfer, and then the glass is separated using a CO2 laser resulting in a chamfered edge.
TL;DR: In this article, a reflective metasurface is designed as the beam launcher to generate a deflected Bessel vortex beam that carries two OAM modes simultaneously, which can combine the advantages of the orthogonality of the vortex beam's multiple orbital-angular-momentum (OAM) modes and the Bessel beam's nondiffraction property.
Abstract: We discuss the generation and measurement of a Bessel vortex beam carrying multiple orbital-angular-momentum (OAM) modes in the radio-frequency domain. Considering that a high-order Bessel beam inherently has high-order OAM modes, in this paper, we propose to superpose these high-order Bessel vortex beams together, which can combine the advantages of the orthogonality of the vortex beam's multiple OAM modes and the Bessel beam's nondiffraction property. A theoretical formula and the basic design method are presented. A reflective metasurface is designed as the beam launcher to generate a deflected Bessel vortex beam that carries two OAM modes of $\ensuremath{\ell}=1$ and $\ensuremath{\ell}=2$ simultaneously. The corresponding reflective metasurface is designed, fabricated, and measured. The full-wave electromagnetic simulations and experimental measurements both verify the effectiveness of the design. The proposed method could further promote the application of a Bessel vortex beam in related near-field scenarios such as near-field wireless communication and radar detection and imaging.
07 May 2021
TL;DR: In this article, a spectral Green's function approach is used to derive the power efficiency under a simultaneous conjugate impedance match between two radiating apertures in the radiative near field.
Abstract: In this work, we study the use of Bessel–Gauss beam launchers for wireless power transfer (WPT) applications. The power transfer efficiency between two radiating apertures is investigated in the radiative near field. A spectral Green’s function approach is used to derive the power efficiency under a simultaneous conjugate impedance match. The transverse electromagnetic (TEM) mode of a coaxial cable, as well as Bessel beam (BB) and Bessel–Gauss beam (BGB) field distributions, are considered as aperture distributions. Numerical results demonstrate that a BGB field distribution is the optimal choice for WPT due to its limited spectrum and reduced diffraction of the radiated beam. We synthesized a Bessel–Gauss launcher that exhibits power efficiency exceeding 50% for distances larger than $30\lambda $ . These results show that non-diffracting beams can pave the way toward efficient near-field WPT systems with extended operating ranges.
TL;DR: In this paper, a femtosecond Bessel beam achieving a 200nm Ra cut surface roughness, which is almost an order of magnitude improvement over the previous bessel beam cutting approaches without losing the uniformity.
Abstract: Previous approaches for laser beam cutting of sapphire often lead to chipping, debris, large kerf widths, tapering and high surface roughness or nonuniform surfaces. Laser beam stealth dicing can remove kerf width and tapering, reduce defects. However, sidewall uniformity is poor as part of the material is laser cut and part is broken by an external mechanical force. In previous approaches of Bessel beam full depth cutting of sapphire, uniformity can be improved. However, the sidewall surface roughness is poor. There has been lack of an ideal solution to achieving minimum defects and low surface roughness. Here we show a much improved sapphire cutting method with a femtosecond Bessel beam achieving a 200 nm Ra cut surface roughness, which is almost an order of magnitude improvement over the previous Bessel beam cutting approaches without losing the uniformity. By using a diameter reduced Gaussian beam passing through a 20° physical angle axicon lens, a highly uniform non-diffraction Bessel beam is generated. Under circular polarization, the effects of Bessel beam scanning speed on flexural strength and the sidewall surface roughness are analyzed for cutting sapphire sheets of 0.38 mm, 1 mm, and 1.5 mm in thickness. Zero taper, zero kerf width, free of debris/chipping sapphire cutting with both straight and curved lines are demonstrated. The fundamental mechanisms involved are discussed. The uniformity of Bessel beam and appropriate separation of pulses have been identified as the key factors for achieving the low surface roughness.
TL;DR: In this paper, the Laguerre-Gaussian (LG), Bessel and Bessel beams are compared to their Gaussian beam counterpart in terms of on-axis intensity and scintillation, while the initial spot sizes of the Gaussian, LG and BG beams are limited to the same spatial extent.
Abstract: The study of beams carrying orbital angular momentum (OAM) has been of interest for its use in free-space optical communications (FSOC), directed energy applications, and remote sensing (RS). For FSOC and RS, it is necessary to measure the wavefront of the beam to recover transmitted or environmental information, respectively. In this computational study, common OAM beams such as the Laguerre–Gaussian (LG), Bessel–Gaussian (BG), and Bessel beams are propagated through atmospheric turbulence and compared to their Gaussian beam counterpart. The turbulence is simulated using multiple phase screens within the framework of a split-step method. Beam metrics used to quantify beam propagation will include the spatial coherence radius, OAM spectrum, on-axis intensity, spot size, divergence, and on-axis scintillation. Atmospheric turbulence along the path is limited to the weak scintillation limit, where beam parameters can be predicted analytically using the Rytov approximation. The results show that BG beams and multiplexed BG beams retain more OAM information than their LG and Bessel beam counterparts. The LG beam on-axis intensity and on-axis scintillation are seen to be independent of OAM mode. The scintillation of the LG beam is less than a BG, Bessel, and Gaussian beam across low- and high-order OAM modes. Insight into these results is discussed through studying the beam divergence, while the initial spot sizes of the Gaussian, LG, and BG beams are limited to the same spatial extent.
TL;DR: In this article, the concave antireflective sub-wavelength structures (ASS) on ZnS have been experimentally investigated to obtain high transmittance in the far-infrared spectral range from 6 μm to 10 μm.
Abstract: As an important mid-infrared to far-infrared optical window, ZnS is extremely important to improve spectral transmission performance, especially in the military field. However, on account of the Fresnel reflection at the interface between the air and the high-strength substrate, surface optical loss occurs in the ZnS optical window. In this study, the concave antireflective sub-wavelength structures (ASS) on ZnS have been experimentally investigated to obtain high transmittance in the far-infrared spectral range from 6 μm to 10 μm. We proposed a simple method to fabricate microhole array ASS by femtosecond Bessel beam, which further increased the depth of the microholes and suppressed the thermal effects effectively, including the crack and recast layer of the microhole. The influence of different Gaussian and Bessel beam parameters on the microhole morphology were explored, and three ASS structures with different periods were prepared by the optimized Bessel parameters. Ultimately, the average transmittance of the sample with the ASS microhole array period of 2.6 μm increased by 4.1% in the 6 μm to 10 μm waveband, and the transmittance was increased by 5.7% at wavelength of 7.2 μm.
TL;DR: In this article, a substrate integrated waveguide (SIW) slot array antenna is proposed to generate the transverse linearly-polarized Bessel beam, which can be easily realized by such an array.
Abstract: The transverse linearly-polarized beam can maintain its polarization when reflected, which is important for a detection system. Most of the existing planar Bessel beam generators are implemented in a central feeding radial topology and hard to generate the Bessel beam with the transverse linear polarization. In this communication, a substrate integrated waveguide (SIW) slot array antenna is proposed to generate the transverse linearly-polarized Bessel beam. The desired phase and amplitude distribution of the Bessel beam can be easily realized by such an array. With the inherent 0°/180° output phase of the comb-like divider considered, the desired 0°/180° phase distribution is implemented by placing adjacent slots on the opposite (0°) or the same side (180°) within a linear array and by employing adjacent linear arrays with the inverse (180°) or the same (0°) slot offset direction accordingly. The offset of the slot, as well as the tuning metalized vias within the comb-like divider, is modulated to generate the desired amplitude distribution. After reducing the influence of the rectangularly-truncated aperture by adding a Gauss-tapered amplitude distribution, a transverse linearly-polarized Bessel beam SIW slot array antenna is designed with more than 100 mm depth-of-field (DoF) and less than -25 dB cross-polarization. To the best of our knowledge, it is the first design to generate the transverse linearly-polarized Bessel beam by a planar array antenna.
TL;DR: In this paper, the effect of radial anisotropy on the optical force exerted on the anisotropic-core/plasmonic-shell nanoparticles under the illumination of the zeroth order Bessel beam based on extended Mie theory and Maxwell's stress tensor method was investigated.
01 Aug 2021
TL;DR: In this paper, the influence of the beam center, beam order, beam polarization type, and half cone angle of the vector Bessel beam on the characteristics of photonic nanojet (PNJ) was analyzed.
Abstract: The photonic nanojet (PNJ) produced by a vector Bessel beam irradiating a dielectric spheroidal particle is investigated using the Discrete Dipole Approximation. The influence of the beam center, beam order, beam polarization type, and half cone angle of the vector Bessel beam on the characteristics of PNJ is analyzed. Several characteristics of PNJ including maximum intensity, the focal length, the effective length, and full width at half maximum are considered. The results show that the characteristics of the PNJ can be controlled by changing the four parameters of the Bessel beam. We think it will help to enhance the application of Bessel beams in generating PNJ and provide new properties to generate PNJ.
TL;DR: The non-diffracting Bessel beam and the Airy beam have been successfully demonstrated in the volumetric imaging applications with faster speed since a single 2D scan provides information in the whole volume that adopted 3D scan in a traditional laser scanning microscopy.
Abstract: The light propagation in the medium normally experiences diffraction, dispersion, and scattering. It is a century-old problem to study the light propagation as the photons may attenuate and wander. We will start from the fundamental concepts of the non-diffracting beams, and examples of the non-diffracting beams include but not limited to the Bessel beam, Airy beam, Mathieu beams. We then discuss about the biomedical applications of the non-diffracting beams with a focus on the linear and nonlinear imaging, e.g., light-sheet fluorescence microscopy, two-photon fluorescence microscopy. The non-diffracting photons may provide scattering resilient imaging as well as the fast speed in the volumetric two-photon fluorescence microscopy. The non-diffracting Bessel beam and the Airy beam have been successfully demonstrated in the volumetric imaging applications with faster speed since a single 2D scan provides information in the whole volume that adopted 3D scan in a traditional laser scanning microscopy. This is an important advancement in the imaging applications with sparse sample structures, especially in neuron imaging. Moreover, the fine axial resolution can be achieved by using the self-accelerating Airy beams or the deep learning algorithms. These additional features to the existing microscopy directly realize a great advantage over the field especially for the recording of the ultrafast neuronal activities including the calcium voltage signal imaging. Nonetheless, with the illumination of dual Bessel beams at non-identical orders, the transverse resolution can also be improved by the concept of image subtraction, which would provide clearer images in the neuronal imaging.
15 Feb 2021
TL;DR: In this paper, the authors demonstrate optical trapping of rare earth-doped NaYF4:Er/Yb nanorods using a quasi Bessel beam (QBB) generated by positive axicon optical fiber tips.
Abstract: We demonstrate optical trapping of rare earth-doped NaYF4:Er/Yb nanorods of high aspect ratio (length 1.47 μm and diameter 140 nm) using a quasi Bessel beam (QBB) generated by positive axicon optical fiber tips. Propulsion or trapping of the nanorods is demonstrated using either single or dual fiber nano-tip geometries. The optical force exerted on the trapped nanorods, their velocities, and their positions have been analyzed. We determine the trap stiffness for a single nanorod to be 0.12 pN/μm (0.003 pN/μm) by power spectrum analysis and 0.13 pN/μm (0.015 pN/μm) by Boltzmann statistics in the direction perpendicular to (along) the fiber axes for an average optical power of 34 mW. The experiments illustrate the advantage of using a QBB for multiple nanorod trapping over a large distance of up to 30 μm.
TL;DR: In this paper, the amplitude-phase distributions of the field in real perfect beams were calculated numerically in the approximation of the scalar diffraction theory, and a distribution closest to an ideal vortex was obtained using a holographic axicon.
Abstract: Transformation of a Bessel beam by a lens results in the formation of a “perfect” vortex beam (PVB) in the focal plane of the lens. The PVB has a single-ring cross-section and carries an orbital angular momentum (OAM) equal to the OAM of the “parent” beam. PVBs have numerous applications based on the assumption of their ideal ring-type structure. For instance, we proposed using terahertz PVBs to excite vortex surface plasmon polaritons propagating along cylindrical conductors and the creation of plasmon multiplex communication lines in the future (Comput. Opt. 2019, 43, 992). Recently, we demonstrated the formation of PVBs in the terahertz range using a Bessel beam produced using a spiral binary silicon axicon (Phys. Rev. A 2017, 96, 023846). It was shown that, in that case, the PVB was not annular, but was split into nested spiral segments, which was obviously a consequence of the method of Bessel beam generation. The search for methods of producing perfect beams with characteristics approaching theoretically possible ones is a topical task. Since for the terahertz range, there are no devices like spatial modulators of light in the visible range, the main method for controlling the mode composition of beams is the use of diffractive optical elements. In this work, we investigated the characteristics of perfect beams, the parent beams being quasi-Bessel beams created by three types of diffractive phase axicons made of high-resistivity silicon: binary, kinoform, and “holographic”. The amplitude-phase distributions of the field in real perfect beams were calculated numerically in the approximation of the scalar diffraction theory. An analytical expression was obtained for the case of the binary axicon. It was shown that a distribution closest to an ideal vortex was obtained using a holographic axicon. The resulting distributions were compared with experimental and theoretical distributions of the evanescent field of a plasmon near the gold–zinc sulfide–air surface at different thicknesses of the dielectric layer, and recommendations for experiments were given.
15 Apr 2021
TL;DR: In this article, the authors proposed a new optical system composed of an existing axicon doublet and a newly proposed amplitude filter, which is expected to have practical applications in tracking far-distance moving targets.
Abstract: We put forward a new optical system, which is composed of an existing axicon doublet and a newly proposed amplitude filter. The axicon doublet consists of a positive axicon and a negative axicon with high and low refractive indices, respectively. The Bessel beam generated by the axicon doublet propagates as far as more than 200 meters, owing to a small refractive index difference between the double axicons. The newly proposed amplitude filter is used to flatten the axial intensity distribution. Numerical results calculated by the complete Rayleigh-Sommerfeld method demonstrate that the generated Bessel beam propagates stably within a very long axial range. The proposed optical system is expected to have practical applications in tracking far-distance moving targets.
TL;DR: This work demonstrates actively tunable wavefront control with high-efficiency by combining catenary-based meta-atoms for intrinsic continuous phase regulation with the chalcogenide phase change material (PCM) of Ge2Sb2Te5.
Abstract: Active wave manipulation by ultracompact meta-devices is highly embraced in recent years, but a major concern still exists due to the lack of functional reconfigurability. Moreover, the phase or amplitude discontinuities introduced by collective response of discrete meta-atoms make current meta-devices far from practical applications. Here, we demonstrate actively tunable wavefront control with high-efficiency by combining catenary-based meta-atoms for intrinsic continuous phase regulation with the chalcogenide phase change material (PCM) of Ge2Sb2Te5. First, switchable beam deflection is demonstrated in a wide mid-IR range between 8 μm and 9.5 μm with ‘on’ and ‘off’ states for beam steering between anomalous and normal specular reflections. Second, a switchable meta-axicon for zero order Bessel beam generation is demonstrated with full width at half maximum (FWHM) as small as ∼0.41 λ (λ = 12 µm). As a result, our scheme for active and continuous phase control potentially paves an avenue to construct active photonic devices especially for applications where large contrast ratio is highly desirable, such as optoelectronic integration, wavefront engineering and so on.
TL;DR: In this article, a metal/magneto-optical (MO) hybrid Pancharatnam-Berry (PB) phase structure was proposed to control the conversion of THz chiral states with the highest efficiency of over 80%.
Abstract: Nowadays, the manipulation of the chiral light field is highly desired to characterize chiral substances more effectively, since the chiral responses of most molecules are generally weak. Terahertz (THz) waves are related to the vibration-rotational energy levels of chiral molecules, so it is significant to actively control and enhance the chirality of THz field. Here, we propose a metal/magneto-optical (MO) hybrid Pancharatnam-Berry (PB) phase structure, which can serve as tunable broadband half-wave plate and control the conversion of THz chiral states with the highest efficiency of over 80%. Based on this active PB element, MO PB metasurfaces are proposed to manipulate THz chiral states as different behaviors: beam deflector and scanning, Bessel beam, and vortex beam. Due to the magnetic-tunablibity, these proposed MO PB metasurfaces can be turned from an “OFF” to “ON” state by changing the external magnetic field. We further investigate the near-field optical chirality and the chirality enhancement factors in far field of the chiral Bessel beam and vortex beam, achieving the superchiral field with the highest chiral enhancement factor of 40 for 0th Bessel beam. These active, high efficiency and broadband chiral PB metasurfaces have promising applications for manipulation the THz chiral light and chiroptical spectroscopic techniques.
TL;DR: In this paper, an approach for the generation of the infinite Bessel beams in three-dimensional FDTD is presented. But the approach is based on the injection of the Bessel solutions of Maxwell's equations from a cylindrical hollow annulus, which is computationally more efficient than the creation of a Bessel-Gauss beam from a wall.
Abstract: Bessel beams are becoming a very useful tool in many areas of optics and photonics, because of the invariance of their intensity profile over an extended propagation range. Finite-Difference-Time-Domain (FDTD) approach is widely used for the modeling of the beam interaction with nanostructures. However, the generation of the Bessel beam in this approach is a computationally challenging problem. In this work, we report an approach for the generation of the infinite Bessel beams in three-dimensional FDTD. It is based on the injection of the Bessel solutions of Maxwell's equations from a cylindrical hollow annulus. This configuration is compatible with Particle In Cell simulations of laser plasma interactions. This configuration allows using a smaller computation box and is therefore computationally more efficient than the creation of a Bessel-Gauss beam from a wall and models more precisely the analytical infinite Bessel beam. Zeroth and higher-order Bessel beams with different cone angles are successfully produced. We investigate the effects of the injector parameters on the error with respect to the analytical solution. In all cases, the relative deviation is in the range of 0.01-7.0 percent.
TL;DR: The results presented here advance the field of optical trapping manipulation of absorbing magnetic particles, and future applications will involve, for example, the design of new hybrid optomagnetic tweezers.
Abstract: We propose a Bessel beam optical tweezers setup that can stably trap superparamagnetic beads The trap stiffness measured is practically independent of the radius of the Bessel beam and of the bead height (distance from the coverlip of the sample chamber), indicating that the beads can be trapped with high accuracy within a wide range of such parameters On the other hand, the trap stiffness exhibits the expected linear increase with the laser power, despite the non-negligible absorption coefficient of the superparamagnetic beads A geometrical optics model that considers spherical aberration and light absorption by the beads was used to predict the optical forces and trap stiffness, showing excellent agreement with the experimental data We believe the results presented here advance the field of optical trapping manipulation of absorbing magnetic particles, and future applications will involve, for example, the design of new hybrid optomagnetic tweezers
TL;DR: In this article, a synthesis and implementation method for generating Bessel beams based on time-reversal theory incorporating electromagnetic (EM) meta-lens is proposed, which can be used for the application of Bessel beam in microwave communications, and it can broaden the application scope of non-diffracting beams.
Abstract: In this paper, a synthesis and implementation method for generating Bessel beams based on time-reversal theory incorporating electromagnetic (EM) meta-lens is proposed. As is known, time-reversal EM waves has the unique characteristic of adaptive backtracking. Therefore, with this characteristic, the EM characteristics of the radiation aperture can be obtained and further utilized to generate Bessel waves with any departure angle. Based on this concept, two meta-lenses for generating Bessel beams tilted in different directions were designed. Both meta-lenses were designed at the center frequency of 15 GHz, and the simulation results were consistent with the target expectation. A representative meta-lens was fabricated and measured. The final size of the meta-lens was 350 mm $\times \,\, 350$ mm, and a Bessel beam with a 30° emergence angle was generated by this structure. The experimental results were in good agreement with the simulation results and the theoretical derivation. This synthetic method of Bessel beam generation using the time-reversal operation may be of great use for the application of Bessel beams in microwave communications, and it can broaden the application scope of non-diffracting beams.
TL;DR: In this article, the vector space-fractional Bessel beam (SFBB) was proposed as a generalized solution of the space fractional wave equation in both integer and fractional dimensional spaces.
Abstract: We introduce an exact analytical solution of the homogeneous space-fractional Helmholtz equation in cylindrical coordinates. This solution, called the vector space-fractional Bessel beam (SFBB), has been established from the Lorenz gauge condition and Hertz vector transformations. We perform scalar and vector wave analysis focusing on electromagnetics applications, especially in cases where the dimensions of the beam are comparable to its wavelength $({k}_{r}\ensuremath{\approx}k)$. The propagation characteristics such as the diffraction and self-healing properties have been explored with particular emphasis on the polarization states and transverse propagation modes. Due to continuous order orbital angular momentum dependence, this beam can serve as a bridge between the ordinary integer Bessel beam and the fractional Bessel beam and, thus, can be considered as a generalized solution of the space-fractional wave equation that is applicable in both integer and fractional dimensional spaces. The proposed SFBBs provide better control over the beam characteristics and can be readily generated using digital micromirror devices, spatial light modulators, metasurfaces, or spiral phase plates. Our findings offer insights on electromagnetic wave propagation, thus paving a route towards applications in optical tweezers, refractive index sensing, optical trapping, and optical communications.