scispace - formally typeset
Search or ask a question

Showing papers on "Bessel beam published in 2014"


Journal ArticleDOI
TL;DR: It is shown that the Airy beam innately yields high contrast and resolution up to a tenfold larger FOV, and its characteristic asymmetric excitation pattern results in all fluorescence contributing positively to the contrast, enabling a step change for light-sheet microscopy.
Abstract: Light-sheet microscopy facilitates rapid, high-contrast, volumetric imaging with minimal sample exposure. However, the rapid divergence of a traditional Gaussian light sheet restricts the field of view (FOV) that provides innate subcellular resolution. We show that the Airy beam innately yields high contrast and resolution up to a tenfold larger FOV. In contrast to the Bessel beam, which also provides an increased FOV, the Airy beam's characteristic asymmetric excitation pattern results in all fluorescence contributing positively to the contrast, enabling a step change for light-sheet microscopy.

672 citations


Journal ArticleDOI
TL;DR: The fundamental working principles of Bessel beam plane illumination microscopy are explained, the pros and cons of each operational mode are discussed, and examples of how to optimize experimental parameters are shown.
Abstract: 3D live imaging is important for a better understanding of biological processes, but it is challenging with current techniques such as spinning-disk confocal microscopy Bessel beam plane illumination microscopy allows high-speed 3D live fluorescence imaging of living cellular and multicellular specimens with nearly isotropic spatial resolution, low photobleaching and low photodamage Unlike conventional fluorescence imaging techniques that usually have a unique operation mode, Bessel plane illumination has several modes that offer different performance with different imaging metrics To achieve optimal results from this technique, the appropriate operation mode needs to be selected and the experimental setting must be optimized for the specific application and associated sample properties Here we explain the fundamental working principles of this technique, discuss the pros and cons of each operational mode and show through examples how to optimize experimental parameters We also describe the procedures needed to construct, align and operate a Bessel beam plane illumination microscope by using our previously reported system as an example, and we list the necessary equipment to build such a microscope Assuming all components are readily available, it would take a person skilled in optical instrumentation ∼1 month to assemble and operate a microscope according to this protocol

277 citations


Journal ArticleDOI
TL;DR: In this article, a common Gaussian beam is transformed into a vector Bessel beam, which is useful for particle trapping, near-field probes, and laser machining, enabling applications such as tractor beams in compact nanoscale devices.
Abstract: Metamaterial surfaces (metasurfaces) can generate tailored electromagnetic wavefronts with spatially varying phase and polarization profiles. In this study a common Gaussian beam is transformed into a vector Bessel beam, which is useful for particle trapping, near-field probes, and laser machining. Going forward, the design and fabrication methodology presented here could be used to create efficient metasurfaces even at optical wavelengths, enabling applications such as tractor beams in compact nanoscale devices.

205 citations


Journal ArticleDOI
TL;DR: In this paper, an electronically controlled acoustic tweezer was used to demonstrate two acoustic manipulation phenomena: superposition of Bessel functions to allow independent manipulation of multiple particles and the use of higher-order Bessel function to trap particles in larger regions than is possible with first-order traps.
Abstract: An electronically controlled acoustic tweezer was used to demonstrate two acoustic manipulation phenomena: superposition of Bessel functions to allow independent manipulation of multiple particles and the use of higher-order Bessel functions to trap particles in larger regions than is possible with first-order traps. The acoustic tweezers consist of a circular 64-element ultrasonic array operating at 2.35 MHz which generates ultrasonic pressure fields in a millimeter-scale fluid-filled chamber. The manipulation capabilities were demonstrated experimentally with 45 and 90-μm-diameter polystyrene spheres. These capabilities bring the dexterity of acoustic tweezers substantially closer to that of optical tweezers.

166 citations


Journal ArticleDOI
TL;DR: It is demonstrated that the nature of light bullets generated from self-focusing in a bulk dielectric medium with Kerr nonlinearity in the anomalous group velocity dispersion regime consists of a sharply localized high-intensity core, which carries the self-compressed pulse and contains approximately 25% of the total energy, and a ring-shaped spatiotemporal periphery.
Abstract: We present a detailed experimental investigation which uncovers the nature of light bullets generated from self-focusing in a bulk dielectric medium with Kerr nonlinearity in the anomalous group velocity dispersion regime. By high dynamic range measurements of three-dimensional intensity profiles, we demonstrate that the light bullets consist of a sharply localized high-intensity core, which carries the self-compressed pulse and contains approximately 25% of the total energy, and a ring-shaped spatiotemporal periphery. Subdiffractive propagation along with dispersive broadening of the light bullets in free space after they exit the nonlinear medium indicate a strong space-time coupling within the bullet. This finding is confirmed by measurements of a spatiotemporal energy density flux that exhibits the same features as a stationary, polychromatic Bessel beam, thus highlighting the nature of the light bullets.

80 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the group velocity of single photons by measuring a change in their arrival time that results from changing the beam's transverse spatial structure and showed that introducing spatial structure to an optical beam, even for a single photon, reduces the group velocities of the light by a readily measurable amount.
Abstract: That the speed of light in free space is constant is a cornerstone of modern physics. However, light beams have finite transverse size, which leads to a modification of their wavevectors resulting in a change to their phase and group velocities. We study the group velocity of single photons by measuring a change in their arrival time that results from changing the beam's transverse spatial structure. Using time-correlated photon pairs we show a reduction of the group velocity of photons in both a Bessel beam and photons in a focused Gaussian beam. In both cases, the delay is several microns over a propagation distance of the order of 1 m. Our work highlights that, even in free space, the invariance of the speed of light only applies to plane waves. Introducing spatial structure to an optical beam, even for a single photon, reduces the group velocity of the light by a readily measurable amount.

79 citations


Journal ArticleDOI
TL;DR: In this article, the authors discussed the possibility of generating a pseudo-Bessel beam, with a propagation distance of several hundreds of wavelengths in microwave and millimeter frequency band, by using a radial line slot array (RLSA).
Abstract: The paper discusses the possibility of generating a pseudo-Bessel beam, with a propagation distance of several hundreds of wavelengths in microwave and millimeter frequency band, by using a radial line slot array (RLSA). A specific application for non-contact microwave detection of buried mines has been considered as test case. The design benefits of a holographic approach to assure the required aperture field distribution and makes use of an ad hoc optimization tool to control the antenna slot layout. The predicted and measured antenna behaviors show that high efficiency and polarization purity can be obtained by such a compact and flat antenna, achieving at the same time both manufacturing and setup simplicity.

70 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed a method to directly transform a linearly polarized Gaussian beam into vector-vortex beams with various spatial patterns via a Digital Micro-mirror Device (DMD) binary holography for generating Laguerre Gaussian, Bessel Gaussian and helical Mathieu Gaussian modes, while a radial polarization converter (S-waveplate) is employed to effectively convert the optical vortices into cylindrically polarized vortex beams.
Abstract: We propose a novel technique to directly transform a linearly polarized Gaussian beam into vector-vortex beams with various spatial patterns. Full high-quality control of amplitude and phase is implemented via a Digital Micro-mirror Device (DMD) binary holography for generating Laguerre-Gaussian, Bessel-Gaussian, and helical Mathieu–Gaussian modes, while a radial polarization converter (S-waveplate) is employed to effectively convert the optical vortices into cylindrically polarized vortex beams. Additionally, the generated vector-vortex beams maintain their polarization symmetry after arbitrary polarization manipulation. Due to the high frame rates of DMD, rapid switching among a series of vector modes carrying different orbital angular momenta paves the way for optical microscopy, trapping, and communication.

63 citations


Patent
17 Mar 2014
TL;DR: In this article, a microscope has a light source for generating a light beam having a wavelength, λ, and beamforming optics configured for receiving the light beam and generating a Bessel-like beam that is directed into a sample.
Abstract: A microscope has a light source for generating a light beam having a wavelength, λ, and beam-forming optics configured for receiving the light beam and generating a Bessel-like beam that is directed into a sample. The beam-forming optics include an excitation objective having an axis oriented in a first direction. Imaging optics are configured for receiving light from a position within the sample that is illuminated by the Bessel-like beam and for imaging the received light on a detector. The imaging optics include a detection objective having an axis oriented in a second direction that is non-parallel to the first direction. A detector is configured for detecting signal light received by the imaging optics, and an aperture mask is positioned

56 citations


Journal ArticleDOI
TL;DR: In this article, conditions for an attractive force acting in opposite direction of the radiating waves, determined by the choice of the beam's half-cone angle, the size of the radiator, and its distance from a fluid sphere, are established and discussed.

50 citations


Journal ArticleDOI
TL;DR: A type of Fresnel zone plate in which its phase is shifted radially outward can easily and precisely turn an incident plane wave into an annular beam at its focal plane and the width of the annulus is a function of focal length.
Abstract: We introduce a type of Fresnel zone plate (FZP) in which its phase is shifted radially outward. This FZP can easily and precisely turn an incident plane wave into an annular beam at its focal plane. High efficiency and flexibility are the advantages of generating doughnut beams by this method. By performing direct calculations and using Bessel function properties, it is shown that a radially shifted zone plate produces annulus focus. Furthermore, by simulating the modified phase structure, in addition to demonstrating the formation of a ring-shaped focus, we also showed that its radius merely depends on the amount of the shift. We also showed that the width of the annulus is a function of focal length. Simulation results were thoroughly examined by experiments. Finally, it is clearly revealed that at a certain distance from the focal plane along the beam propagation, an annular beam is transformed into a Bessel beam, and a focal line is formed.

Journal ArticleDOI
TL;DR: These are the first measurements of hygroscopicity on fine mode and near-accumulation mode aerosols, the size regimes bearing the most atmospheric relevance in terms of loading, light extinction and scattering, and are contrasted with other single particle and ensemble methods.
Abstract: A single horizontally-propagating zeroth order Bessel laser beam with a counter-propagating gas flow was used to confine single fine-mode aerosol particles over extended periods of time, during which process measurements were performed. Particle sizes were measured by the analysis of the angular variation of light scattered at 532 nm by a particle in the Bessel beam, using either a probe beam at 405 nm or 633 nm. The vapour pressures of glycerol and 1,2,6-hexanetriol particles were determined to be 7.5 ± 2.6 mPa and 0.20 ± 0.02 mPa respectively. The lower volatility of hexanetriol allowed better definition of the trapping environment relative humidity profile over the measurement time period, thus higher precision measurements were obtained compared to those for glycerol. The size evolution of a hexanetriol particle, as well as its refractive index at wavelengths 532 nm and 405 nm, were determined by modelling its position along the Bessel beam propagation length while collecting phase functions with the 405 nm probe beam. Measurements of the hygroscopic growth of sodium chloride and ammonium sulfate have been performed on particles as small as 350 nm in radius, with growth curves well described by widely used equilibrium state models. These are the smallest particles for which single-particle hygroscopicity has been measured and represent the first measurements of hygroscopicity on fine mode and near-accumulation mode aerosols, the size regimes bearing the most atmospheric relevance in terms of loading, light extinction and scattering. Finally, the technique is contrasted with other single particle and ensemble methods, and limitations are assessed.

Journal ArticleDOI
TL;DR: In this paper, the transformation of paraxial and non-paraxial Bessel beams in a crystal of Iceland spar is considered theoretically and an optical system is designed for investigating the intensity distribution after passage through the crystal.
Abstract: The transformation of paraxial and nonparaxial Bessel beams in a crystal of Iceland spar is considered theoretically. Calculation formulae for matching the thickness of the crystal and the parameters of the incident beam required for complete conversion of a circularly polarized zero-order Bessel beam into a second-order vortex beam are obtained. An optical system was designed for investigating the intensity distribution after passage through the crystal. Experimental and theoretical results are in good agreement.

Journal ArticleDOI
TL;DR: In this paper, a Bessel beam of de Broglie matter waves was created by the free evolution of a thin toroidal atomic Bose-Einstein condensate (BEC) which has been set into rotational motion.
Abstract: Bessel beams are plane waves with amplitude profiles described by Bessel functions. They are important because they propagate ‘diffraction-free’ and because they can carry orbital angular momentum. Here we report the creation of a Bessel beam of de Broglie matter waves. The Bessel beam is produced by the free evolution of a thin toroidal atomic Bose–Einstein condensate (BEC) which has been set into rotational motion. By attempting to stir it at different rotation rates, we show that the toroidal BEC can only be made to rotate at discrete, equally spaced frequencies, demonstrating that circulation is quantized in atomic BECs. The method used here can be viewed as a form of wavefunction engineering which might be developed to implement cold atom matter wave holography.

Journal ArticleDOI
TL;DR: Based on the Mie scattering theory and Maxwell stress tensor method, this paper investigated the transverse optical force (TOF) acting on chiral particles illuminated by a zero-order Bessel beam.
Abstract: Based on the Mie scattering theory and Maxwell stress tensor method, we investigate the transverse optical force (TOF) acting on chiral particles illuminated by a zero-order Bessel beam. It is demonstrated that the particle chirality can induce an azimuthal optical force (AOF), resulting in orbital motion of particles around the optical beam axis. The AOF depends strongly on particle loss as well as the handedness of chirality, with its amplitude capable of changing by over an order of magnitude by particle's chiral loss. The other component of TOF, the radial optical force (ROF), is much less sensitive to the magnitude and handedness of the particle chirality as well as the loss when the chirality is small. Analytical result based on dipole approximation reveals that the AOF arises from the direct coupling of particle chirality to both the spin angular momentum (SAM) and optical vorticity (curl of Poynting vector), exhibiting a conversion of optical SAM of an incident beam to mechanical orbital angular momentum of an illuminated particle. Differently, the ROF originates from the transverse gradient force. In addition, particle chirality yields a negative contribution to the gradient force; thus the ROF can be attenuated and even reversed in direction when particle chirality is sufficiently large. These characteristics of TOF might find applications in chirality detection as well as sorting chiral particles of different handedness and separating them from conventional ones.

Journal ArticleDOI
TL;DR: In this article, a new method is proposed to generate self-image 3D optical bottle beam (OBB) by focusing non-diffracting Bessel beam using an axicon.

Journal ArticleDOI
TL;DR: In this article, a hybrid microoptical component consisting of an aspherical and a conical lens integrated into a single monolithic element has been fabricated at the end face of a fiber using the technique of direct laser writing of photopolymers.
Abstract: A novel method to overcome the problem of accurately centering microoptical components built by direct laser writing on the tip of a single mode optical fiber is presented, and it includes employing mode field expansion. A hybrid microoptical component consisting of an aspherical and a conical lens integrated into a single monolithic element has been fabricated at the end-face of a fiber using the technique of direct laser writing of photopolymers. The optical performance of the fabricated microstructures has been measured experimentally. We show that optical properties of Gaussian and Bessel beams can be easily tuned by adjusting the geometrical parameters of fiber-tip microoptical elements. In addition, we experimentally demonstrate the increase of propagation distance of a Bessel beam five-fold, using the fabricated microoptical element. This improvement in the fabrication method of fiber-tip microoptical elements can be used in the manufacturing of integrated micro-optical devices for optical tweezing, laser micromachining and long focal depth optical systems.

Journal ArticleDOI
TL;DR: Results show that the angle of two intensity profiles can be used to describe the self-healing ability of arbitrary beams as the reconstruction distance for quantitatively describing theSelf-heating ability of Bessel beam.
Abstract: Quantitative description of the self-healing ability of a beam is very important for studying or comparing the self-healing ability of different beams. As describing the similarity by using the angle of two infinite-dimensional complex vectors in Hilbert space, the angle of two intensity profiles is proposed to quantitatively describe the self-healing ability of different beams. As a special case, quantitative description of the self-healing ability of a Bessel-Gaussian beam is studied. Results show that the angle of two intensity profiles can be used to describe the self-healing ability of arbitrary beams as the reconstruction distance for quantitatively describing the self-healing ability of Bessel beam. It offers a new method for studying or comparing the self-healing ability of different beams.

Journal ArticleDOI
TL;DR: Nonlinear Bessel vortices are shown to be sufficiently intense to generate a ring-shaped filamentary ionized channel in the medium which is foreseen as opening the way to novel applications in laser material processing of transparent dielectrics.
Abstract: We present a new type of ring-shaped filaments featured by stationary nonlinear high-order Bessel solutions to the laser beam propagation equation. Two different regimes are identified by direct numerical simulations of the nonlinear propagation of axicon focused Gaussian beams carrying helicity in a Kerr medium with multiphoton absorption: the stable nonlinear propagation regime corresponds to a slow beam reshaping into one of the stationary nonlinear high-order Bessel solutions, called nonlinear Bessel vortices. The region of existence of nonlinear Bessel vortices is found semi-analytically. The influence of the Kerr nonlinearity and nonlinear losses on the beam shape is presented. Direct numerical simulations highlight the role of attractors played by nonlinear Bessel vortices in the stable propagation regime. Large input powers or small cone angles lead to the unstable propagation regime where nonlinear Bessel vortices break up into an helical multiple filament pattern or a more irregular structure. Nonlinear Bessel vortices are shown to be sufficiently intense to generate a ring-shaped filamentary ionized channel in the medium which is foreseen as opening the way to novel applications in laser material processing of transparent dielectrics.

Journal ArticleDOI
TL;DR: The extended optical theorem is generalized for scalar acoustical beams of arbitrary character with any angle of incidence interacting with an object of arbitrary geometric shape and size placed randomly in the beam's path with any scattering angle.
Abstract: The extended optical theorem is generalized for scalar acoustical beams of arbitrary character with any angle of incidence interacting with an object of arbitrary geometric shape and size, and placed randomly in the beam's path with any scattering angle. Analytical expressions for the extinction, absorption, and scattering cross sections are derived, and the connections with the axial (i.e., along the direction of wave propagation) torque and radiation force calculations are discussed. As examples to illustrate the analysis for a viscoelastic object, the extinction, absorption, and scattering cross sections are provided for an infinite plane progressive wave, infinite nondiffracting Bessel beams, a zero-order spherical quasi-Gaussian beam, and a Bessel-Gauss vortex beam emanating from a finite circular aperture, which reduces to a finite high-order Bessel beam, a finite zero-order Bessel beam, and a finite piston radiator vibrating uniformly with appropriate selection of beam parameters. The similarity with the asymptotic quantum inelastic cross sections is also mentioned.

Journal ArticleDOI
TL;DR: In this paper, the equilibrium position of an aerosol droplet trapped in a counter-propagating Bessel beam and gas flow is studied both experimentally and theoretically, and it is shown that the position of the droplet is greatly affected by the excitation of whispering gallery modes.
Abstract: The equilibrium position of an aerosol droplet trapped in a counter-propagating Bessel beam and gas flow is studied both experimentally and theoretically. This provides an aerosol analogue to the separation of particles of differing size and refractive index in counter-propagating laser beam and liquid flow, referred to as optical chromatography. Using the model system of a pure glycerol droplet it is found that, as evaporation takes place and the size of the droplet decreases, the size-dependent equilibrium position does not change in a simple monotonic fashion. Instead, the position of the droplet is greatly affected by the excitation of whispering gallery modes. This leads to sharp peaks in the equilibrium position curve, not unlike those that occur in single particle spectroscopy. The conditions necessary to excite whispering gallery modes are thoroughly investigated.

Journal ArticleDOI
TL;DR: In this paper, the inverse Compton scattering of laser light on high-energetic twisted electrons is investigated with the aim of constructing spatially structured x-ray beams with a well-defined spatial structure, in a way not possible with ordinary plane-wave electron beams.
Abstract: The inverse Compton scattering of laser light on high-energetic twisted electrons is investigated with the aim to construct spatially structured x-ray beams. In particular, we analyze how the properties of the twisted electrons, such as the topological charge and aperture angle of the electron Bessel beam, affect the energy and angular distribution of scattered x rays. We show that with suitably chosen initial twisted electron states one can synthesize tailor-made x-ray beam profiles with a well-defined spatial structure, in a way not possible with ordinary plane-wave electron beams.

Journal ArticleDOI
TL;DR: The analysis of the behavior of several physical parameters of mean-level optical radiation shows that the shape stability of a vortex Bessel beam increases with the topological charge of this beam during its propagation in a turbulent atmosphere.
Abstract: Transformation of vortex Bessel beams during propagation in turbulent atmosphere is theoretically analyzed. Deforming influence of the random inhomogeneity of the turbulent medium on propagation of diffraction-free beams leads to disappearance of their invariant properties. In the given research, features of evolution of the spatial structure of distribution of mean intensity of vortex Bessel beams in turbulent atmosphere are analyzed. A quantitative criterion of possibility of carrying over of a dark central domain by vortex Bessel beams in a turbulent atmosphere is derived. The analysis of the behavior of several physical parameters of mean-level optical radiation shows that the shape stability of a vortex Bessel beam increases with the topological charge of this beam during its propagation in a turbulent atmosphere.

Journal ArticleDOI
TL;DR: In this article, the scattering of an on-axis incident zero-order Bessel beam by a concentric sphere is firstly investigated by using an analytical method based on the spherical vector wave functions.
Abstract: The scattering of an on-axis incident zero-order Bessel beam by a concentric sphere is firstly investigated by using an analytical method. Based on the spherical vector wave functions, the expansion expressions of the incident Bessel beam are derived in terms of the electric and magnetic fields that satisfy Maxwell's equations. According to the integral localized approximation, an analytical formula for the calculation of beam shape coefficients is given. The present method is validated by the comparison of the analytical result and the numerical result obtained from the surface integral equation method. The effects of the beam half-angle, the refractive index of inner sphere and the size parameter of concentric sphere on the differential scattering cross section are analyzed in detail. This investigation is expected to provide key theoretical support and practical guidance for the techniques of laser detection on particle and diagnosis.

Journal ArticleDOI
TL;DR: In this article, the characterizations of quasi-Bessel beam (QBB) formed by the ideal axicon and oblate-tip axicon are described, and simple analytical formulas can be used to predict the required laser parameters, including the laser pulse energy, the generated fluence distributions, and the beam diameters.
Abstract: A quasi-Bessel beam (QBB) is suitable for laser ablation because it possesses a micrometer-sized focal spot and long depth of focus simultaneously. In this paper, the characterizations of QBBs formed by the ideal axicon and oblate-tip axicon are described. Strong on-axis intensity oscillations occur due to interference between the QBB and the refracted beam by the oblate tip. Using the axicon for laser ablation was theoretically investigated. Simple analytical formulas can be used to predict the required laser parameters, including the laser pulse energy, the generated fluence distributions, and the beam diameters.

Journal ArticleDOI
TL;DR: A novel concept of a compact optical component aimed at transforming a point-like source into a Bessel beam, called AXIGRIN, consists of an axicon fabricated at the end facet of a gradient index lens that can be directly coupled to an optical fiber, a microscope objective, or vertical-external-cavity surface-emitting-laser to be used without preliminary adjustments.
Abstract: We propose and demonstrate a novel concept of a compact optical component aimed at transforming a point-like source into a Bessel beam. This component, called AXIGRIN, consists of an axicon fabricated at the end facet of a gradient index lens. It can be directly coupled to an optical fiber, a microscope objective, or vertical-external-cavity surface-emitting-laser to be used without preliminary adjustments, which is of practical interest for end users. This opens new avenues in domains, such as imaging, particle acceleration and manipulation, optical coherence tomography, data storage, laser cutting, etc. AXIGRIN also opens the perspective of using Bessel beams for endoscopy. The generation of linearly and radially polarized Bessel beams is demonstrated with a fiber AXIGRIN.

Journal ArticleDOI
TL;DR: In this paper, the authors report on recent progress in the generation of non-diffracting (Bessel) beams from semiconductor light sources including both edge-emitting and surface emitting semiconductor lasers as well as light emitting diodes (LEDs).

Journal ArticleDOI
TL;DR: The shape of the fabricated axicons was demonstrated to be controllable through laser exposure, proximity, and apex angle of the source axicon, and the fabricatedAxicons are capable of generating a quality Bessel beam with an excellent focusing performance.
Abstract: A novel direct-laser writing fabrication process for micro-axicons is demonstrated. A fiber-axicon-generated Bessel beam was utilized to write on UV-curable optical epoxy to form new axicons and axicon arrays, and geometrical parameters of the replicated epoxy axicons were analyzed in terms of both apex angle and proximity of the writing axicons. The shape of the fabricated axicons was demonstrated to be controllable through laser exposure, proximity, and apex angle of the source axicon, and the fabricated axicons are capable of generating a quality Bessel beam with an excellent focusing performance.

Journal ArticleDOI
TL;DR: In this article, the axial and transverse radiation forces on a fluid sphere placed arbitrarily in the acoustical field of Bessel beams of standing waves are evaluated using a partial-wave expansion (PWE) method.

Journal ArticleDOI
TL;DR: In this paper, the authors introduced a new family of diffraction-free asymmetric elegant Bessel beams (EB-beams) with fractional orbital angular angular momentum (OAM).
Abstract: This paper introduces a new family of diffraction-free asymmetric elegant Bessel beams (EB-beams) with fractional orbital angular momentum (OAM). EB-beams are modes of free space and described by the n-th order Bessel function of the first kind with a complex argument. Functions of complex amplitudes of EB-beams are orthogonal by co ntinuous scaling parameter and not orthogonal on a discrete parameter (topological charge). The intensity distribution of EB-beams has a countable number of isolated zeros of intensity, located on the horizontal axis. These zeros are centers of optical vortices with unit topological charge and opposite signs on different sides of the origin. Isolated intensity zero on the optical axis generates an optical vortex with topological charge of n . OAM of the EB-beams is ( n + 0,69777)ħ per photon, where ħ is the Planck's constant.