Nondiffracting Beams Research Articles

Manipulation of Non-Diffracting Beams with Arbitrary Structures Based on Optical Caustics

Manipulation of Non-Diffracting Beams with Arbitrary Structures Based on Optical Caustics

Applications of Non-Diffracting Beams in Biological Microscopic Imaging

Applications of Non-Diffracting Beams in Biological Microscopic Imaging

Fiber-integrated catenary ring-array metasurfaces for beam shaping.

Catenary is referred to as "the real mathematical and mechanical form" in the architectural field. Because of the unique phase control characteristic of the catenary, it has excellent ability in optical manipulation. Here, we propose an optical waveform conversion device based on optical fiber-integrated catenary ring-array metasurfaces. The device consists of a cascade structure of a single-mode fiber (SMF) and a graded-index fiber (GIF). At the GIF end, two kinds of catenary ring-array metasurfaces are introduced to realize beam shaping from Gaussian beam (GB) to Bessel beam. The device can selectively generate a focused or non-diffracting Bessel beam by changing the circular polarization state of the incident light. It is worth noting that under some parameters of the device, the output Bessel beam can break through the diffraction limit, which has potential applications in the fields of optical imaging, optical communication, and optical trapping.

Modeling of two-photon polymerization in the strong-pulse regime

This paper reports a study of two-photon polymerization induced by femtosecond laser pulses having microjoule pulse energy and kilohertz repetition rates. Light-matter interaction and polymerization kinetics are modeled in highly confined spatiotemporal scales. The model employs a non-diffractive Bessel beam, considers the effects of temperature-dependent species diffusions, and regards propagation and termination kinetic constants as functions of double-bond conversion. The model is validated by comparing the size of features predicted from simulations to those generated experimentally. The model is used to investigate how the time and energy required to create a single volume element ("voxel") change under various conditions of irradiation. The results show that polymerizing a single voxel requires a minimum exposure time that is constant across a range of irradiation conditions, and is largely determined by the chemical kinetics. In the regime where the pulse energy is low (< 10 μ J), it is more energy-efficient to use fewer pulses having higher energy within the same total exposure time. However, this trend reverses in the regime where the pulse energy is high (10 μ J - 30 μ J), because radical-radical recombination becomes significant, which wastes absorbed energy. This work advances the understanding of two-photon polymerization in the strong-pulse regime and is a step toward increasing throughput to a level suitable for industrial applications. • Two-photon polymerization is induced by few and strong femtosecond laser pulses • A Bessel beam is utilized to rapidly fabricates high aspect ratio structures • Polymerizing a single voxel requires a minimum exposure time • It is more energy-efficient to use fewer pulses when the pulse energy is low (<10 μ J) • Radical-radical recombination is severe when the pulse energy is high (>10 μ J)

Improving longitudinal resolution of Airy beams two-photon volume imaging with fluorescence lifetime imaging

The non-diffracting Airy beams have been reported to increase acquisition speed by projecting the axially significantly elongated information to a two-dimensional (2D) image. Due to the elongated focal length, an Airy volumetric image can cover information as much as stack images with multiple Gaussian images at different imaging depths, which significantly increases the volumetric imaging rate. However, the projection of three-dimensional (3D) structures on a 2D plane is usually indistinguishable, especially those that overlap along the axis. Therefore, we proposed an axially resolved volume imaging technique based on a two-photon fluorescence lifetime microscopy imaging (FLIM) by using Airy beams.

Terahertz structured light: nonparaxial Airy imaging using silicon diffractive optics

Structured light – electromagnetic waves with a strong spatial inhomogeneity of amplitude, phase, and polarization – has occupied far-reaching positions in both optical research and applications. Terahertz (THz) waves, due to recent innovations in photonics and nanotechnology, became so robust that it was not only implemented in a wide variety of applications such as communications, spectroscopic analysis, and non-destructive imaging, but also served as a low-cost and easily implementable experimental platform for novel concept illustration. In this work, we show that structured nonparaxial THz light in the form of Airy, Bessel, and Gaussian beams can be generated in a compact way using exclusively silicon diffractive optics prepared by femtosecond laser ablation technology. The accelerating nature of the generated structured light is demonstrated via THz imaging of objects partially obscured by an opaque beam block. Unlike conventional paraxial approaches, when a combination of a lens and a cubic phase (or amplitude) mask creates a nondiffracting Airy beam, we demonstrate simultaneous lensless nonparaxial THz Airy beam generation and its application in imaging system. Images of single objects, imaging with a controllable placed obstacle, and imaging of stacked graphene layers are presented, revealing hence potential of the approach to inspect quality of 2D materials. Structured nonparaxial THz illumination is investigated both theoretically and experimentally with appropriate extensive benchmarks. The structured THz illumination consistently outperforms the conventional one in resolution and contrast, thus opening new frontiers of structured light applications in imaging and inverse scattering problems, as it enables sophisticated estimates of optical properties of the investigated structures.

A new family of two-dimensional Laguerre beams

We found a new family of non-diffracting Laguerre beams, which are constructed by the associated Laguerre polynomials and trigonometric functions, and described by different radial mode numbers and negative topological charges. Surprisingly, the description with negative topological charges is very different from the description of the general non-diffracting Laguerre beams with positive topological charges. The evolution laws for the new family of non-diffracting beams with the negative topological charges is depicted graphically, and the excitation mechanism of this new family is revealed, which might be helpful in improving the understanding of two-dimensional non-diffracting solutions of the paraxial wave equation.

Generation of non-diffractive Lommel beams based on all-dielectric metasurfaces.

Lommel beam is a non-diffractive vortex beam of high concern recently, widely used in communication and turbulence studies. However, conventional methods of generating Lommel beams, such as using spatial light modulators (SLMs), are limited by their low resolution, poor phase manipulation, and small numerical aperture (NA). Here, non-diffractive Lommel beams based on all-dielectric metasurfaces are proposed. Using the Pancharatnam-Berry (PB) phase arrangement, the focal depth of the main lobe of the generated beam can reach 75 µm (∼119λ). Additionally, the broadband characteristics of the designed metasurface between 550 and 710 nm are observed. The resulting beam is demonstrated to show excellent self-healing properties by placing up obstacles. We also combine the phase of the Dammann grating with that of the Lommel beam to create a metasurface capable of producing a 1 × 4 Lommel beam array; the generated beams are still characterized by uniformity and non-diffraction. This study provides a new idea for Lommel beam generation with promising applications in optical communication, optical tweezers, and laser fabrication.

Generation of Bessel beams via femtosecond direct laser writing 3D phase plates.

Featuring diffracting-free propagation and self-reconstruc-tion, Bessel beams (BBs) have sparked great interest in the scientific community. These properties give the potential for application in optical communications, laser machining, and optical tweezers. However, generating such beams with high quality is still challenging. Here, by using the femtosecond direct laser writing (DLW) based on two-photon polymerization (TPP) technique, we convert phase distributions of ideal BBs with different topological charges into polymer phase plates. The experimentally generated zeroth- and higher-order BBs are propagation-invariant up to 800 mm. Our work may facilitate the applications of non-diffracting beams in integrated optics.

Diffraction-free beam propagation at the exceptional point of non-Hermitian Glauber Fock lattices

We construct localized beams in a non-Hermitian Glauber Fock (NGF) lattice of coupled waveguides and show that they can propagate over a long distance withalmost no diffraction. We specifically obtain the diffraction-free beams in a finite NGF lattice at the exceptional point (EP) by using the exact eigenstates of the semi-infinite unidirectional NGF lattice. We provide a numerical approach to finding other lattices that are capable of supporting non-diffracting beams at EPs.

Noise-tolerant single-photon imaging by using non-diffractive pulsed laser beams

Accurate optical imaging capable of reconstructing three-dimensional (3D) target objects with strong surrounding noises are highly demanding in diverse applications. For conventional imagers with narrow probe beams, the probe beams usually suffer from serious spreading and distortion due to the diffraction and surrounding noises. Here, we construct a 3D imager by using pulsed Bessel beams, enabling reconstruction of high-resolution 3D profiles with sub-millimeter transverse resolution and sub-centimeter depth resolution. We demonstrate that due to the outstanding diffraction-free and self-healing properties of Bessel beams, the present imager can provide high-quality reconstructed images in high-noise environments with opaque scatters. The method developed here for reducing the effects of surrounding noises can also be exploited in the light detection and ranging technology at single-photon level.

Design and Implementation of a Quasi Nondiffraction Beam for Microwave Power Transmission Application

In this letter, a quasi nondiffraction beam is designed and implemented for microwave power transmission (MPT) application. To generate a quasi nondiffraction beam, a new formula is derived to calculate the phase distribution on the metasurface (MS), and a phase shifting unit with 360° transmission phase coverage and transmission amplitude better than −3 dB is designed to achieve desired phase. The simulated and measured results demonstrate that a quasi nondiffraction beam can be generated by the proposed MS. In order to prove that the quasi-nondiffraction beam can be used for microwave power transfer, a miniaturized MPT system is built and measured. The system-level measurement results indicate that the proposed transmitting antenna helps the receiving terminal to harvest more power and improves the power transmission efficiency of the system.

Acoustic Gaussian-Airy beams

Acoustic Airy beams as non-diffractive beams possess self-bending, self-healing, and non-diffraction virtues and are expected to have great potential in applications like ultrasonic imaging. Here an analytical theory is provided for Gaussian modulated Airy (gAiry) acoustic beams. It is revealed through numerical calculations and finite element simulations that gAiry beams inherit the merits mentioned above of standard Airy beams. In theoretically predicted and more practical cases where sources of limited apertures generate beams, reduction of side lobes is found in gAiry fields, while bilateral focusing using a pair of beams shows improved field features when compared with focused Airy fields. The theories and observations here can help deploy gAiry beams in applications.

Picosecond Bessel Beam Fabricated Pure, Gold-Coated Silver Nanostructures for Trace-Level Sensing of Multiple Explosives and Hazardous Molecules.

A zeroth-order, non-diffracting Bessel beam, generated by picosecond laser pulses (1064 nm, 10 Hz, 30 ps) through an axicon, was utilized to perform pulse energy-dependent (12 mJ, 16 mJ, 20 mJ, 24 mJ) laser ablation of silver (Ag) substrates in air. The fabrication resulted in finger-like Ag nanostructures (NSs) in the sub-200 nm domain and obtained structures were characterized using the FESEM and AFM techniques. Subsequently, we employed those Ag NSs in surface-enhanced Raman spectroscopy (SERS) studies achieving promising sensing results towards trace-level detection of six different hazardous materials (explosive molecules of picric acid (PA) and ammonium nitrate (AN), a pesticide thiram (TH) and the dye molecules of Methylene Blue (MB), Malachite Green (MG), and Nile Blue (NB)) along with a biomolecule (hen egg white lysozyme (HEWL)). The remarkably superior plasmonic behaviour exhibited by the AgNS corresponding to 16 mJ pulse ablation energy was further explored. To accomplish a real-time application-oriented understanding, time-dependent studies were performed utilizing the AgNS prepared with 16 mJ and TH molecule by collecting the SERS data periodically for up to 120 days. The coated AgNSs were prepared with optimized gold (Au) deposition, accomplishing a much lower trace detection in the case of thiram (~50 pM compared to ~50 nM achieved prior to the coating) as well as superior EF up to ~108 (~106 before Au coating). Additionally, these substrates have demonstrated superior stability compared to those obtained before Au coating.

Sharp-edge diffraction under Bessel beam illumination: a catastrophe optics perspective.

Boundary diffraction wave theory and catastrophe optics have already proved to be a formidable combination in computational optics. In the present paper, a general paraxial theory aimed at dealing paraxial diffraction of Bessel beams by arbitrarily shaped sharp-edge apertures is developed. A key ingredient of our analysis is the δ-like nature of the angular spectrum of nondiffracting beams. This allows the diffracted wavefield to be effectively represented through two-dimensional integrals defined onto rectangular domains, whose numerical evaluation is easily achievable via standard Monte Carlo techniques. As a byproduct of the present analysis, a simple explanation of a recently observed property of some "heart-like" apertures to flatten the axial intensity of apodized Bessel beams is also provided.

Exploration for adequate non-diffractive beam generation in dense scattering media

The propagation methods of a non-diffractive beam (NDB) for optical sensing in scattering media have been extensively studied. However, those methods can realize the high resolution and long depth of focus in the viewpoint of microscopic imaging. In this study, we focus on macroscopic sensing in living tissues with a depth of a few tens centimeters. An experimental approach for generating adequate NDB in dense scattering media based on the linear relationship between propagation distance and transport mean free path is reported. For annular beams with different diameters, the same changes of the center intensity ratio of NDB are obtained from the experiment results. They are discussed with theoretical analysis. As a result, the maximum center intensity ratio of the adequate generated NDB can be estimated at arbitrary propagation distance in the dense scattering media.

Characterization of white-light non-diffracting beams generated using a deformable mirror

White-light non-diffraction beams such as Airy beam and Bessel beam have potential applications in multispectral imaging and micromanipulation. Generation of white-light Airy beam and Bessel beam with high quality and high efficiency still remains challenging for conventional diffractive or refractive optics which suffers from significant chromatic dispersion. In this paper, both high-quality white-light Airy beam and Bessel beam are generated using a deformable mirror by modulating the incident LED beam with tunable cubic and conical wavefronts. The main lobe of the generated white-light non-diffraction beams does not suffer from chromatic dispersion along the propagation. The results also show that the generation of the white-light Bessel beam has higher requirements for spatial coherence than white-light Airy beams. Our work expands the understanding of the white-light non-diffraction beams and paves the way for the applications.

Surface acoustic wave quasi-Bessel beams generated by symmetrically tilted interdigital transducers

Formation of surface acoustic wave (SAW) quasi-Bessel beams on a piezoelectric substrate through superposition of plane waves generated by interdigital transducers tilted symmetrically about the propagation axis is numerically and experimentally demonstrated. Acting as an axicon, the tilted transducers provide a facile way for quasi-Bessel beam generation. Finite-element method simulations reveal that non-diffracting Bessel beams, whose length and width are 193 and 1.38 wavelengths, respectively, can be obtained on a YX-128∘ lithium niobate substrate for an axicon angle of 15 degrees. The corresponding values for 20 degrees are 146 and 1.05 wavelengths, respectively. For a wavelength of approximately 300 micrometers, transmission spectra show that Bessel beam formation can be achieved at frequencies around 13.3 MHz. Bessel beam is visualized through a thin liquid film of methanol on the substrate. SAW Bessel beams can be utilized in acoustophoresis in microfluidic systems and sensing applications.

Study of Self-healing Behavior for Airy Beams in Atmospheric Turbulence

The Airy beam shows its peculiar property of self-healing which attracts lots of attentions to do the researches about the higher dimensional nondiffraction beams which can apply to lots of aspects to doing researches. We demonstrate the self-healing property of Airy beam which displays similar profiles both in weak and strong turbulence in atmosphere. Highly similarity has been shown when the propagation distance is not very long. The self-healing exhibits its own profile in strong turbulence and stability in weak turbulence respectively with the longer propagation distance. However, the variation of exponential truncation factors and the transverse scales would not change the conclusion that the self-healing property would vanish at the same propagation distance both in weak and strong turbulence. It means that they would reach zero intensity plane with the same self-healing critical distance zs and would not entirely disappear until reach the same disappearance critical distance zd . This study provide a method to enhance the self-healing property of Airy beams.

Generation of random soliton-like beams in a nonlinear fractional Schrödinger equation.

We investigate the generation of random soliton-like beams based on the Kuznetsov-Ma solitons in a nonlinear fractional Schrödinger equation (NLFSE). For Lévy index α = 1, the Kuznetsov-Ma solitons split into two nondiffracting beams during propagation in linear regime. According to the different input positions of the Kuznetsov-Ma solitons, the diffraction-free beams can be divided into three different types: bright-dark, dark-bright and bright-bright beams. In the nonlinear regime, the Kuznetsov-Ma solitons can be evolved into random soliton-like beams due to the collapse. The number of soliton-like beams is related to the nonlinear coefficient and the Lévy index. The bigger the nonlinear coefficient, the more beams generated. Moreover, the peak intensity of soliton-like beams presents a Gaussian distribution under the large nonlinear effect. In practice, the evolution of KM soliton can be realized by a plane wave with a Gaussian perturbation, which can be confirmed that they have the similar dynamics of propagation. In two dimensions, the plane wave with a Gaussian perturbation can be evolved into a bright-dark axisymmetric ring beam in the linear regime. Under the nonlinear modulation, the energy accumulates to the center and finally breaks apart into random beam filaments.