A new approach to bessel beams

This work innovatively designs an all-dielectric metasurface fabricated using 3D printing technology with alumina as the substrate material. This metasurface successfully generates vectorial non-diffracting Bessel beams at a specific frequency of 0.1THz. Initially, through comprehensive simulation analysis of the interaction between the metasurface and the incident beam, it was discovered that the metasurface can precisely manipulate the properties of the transmitted beam based on the polarization state of the incident beam. Specifically, when illuminated by a left-handed circularly polarized (LCP) Gaussian beam, the transmitted beam manifests as a radially polarized Bessel beam. Conversely, under right-handed circularly polarized (RCP) Gaussian beam illumination, the transmitted light transforms into an azimuthally polarized Bessel beam. Building upon the theoretical simulations and considering experimental constraints, further experimental validation was conducted using linearly polarized light, confirming the effectiveness and feasibility of the proposed design. Experimental results demonstrate that the presented all-dielectric alumina metasurface, fabricated via 3D printing, successfully achieves the generation of vector nondiffracting Bessel beams. On one hand, the combination of alumina material and 3D printing technology significantly reduces manufacturing costs, laying a foundation for large scale application. On the other hand, leveraging the high precision of 3D printing ensures the accurate fabrication of the metasurface structure, thereby guaranteeing the high quality and stability of the generated vector beams. This work provides a novel approach for the efficient generation of Bessel beams and is expected to have profound implications in the field of terahertz technology.

We demonstrate how to create non-diffracting vector Bessel beams by implementing a spatial light modulator (SLM) to generate scalar Bessel beams which are then converted into vector fields by the use of an azimuthally-varying birefringent plate, known as a q-plate. The orbital angular momentum (OAM) of these generated beams is measured by performing a modal decomposition on each of the beam’s polarization components. This is achieved by separating the circular polarization components through a polarization grating (PG) before performing the modal decomposition. We investigate both single charged Bessel beams as well as superpositions and the results are in good agreement with theory.

The Bessel beam has become significant in optical research due to its properties such as a long focal depth, self-healing, and non-diffraction. However, conventional methods for generating Bessel beams have drawbacks such as limited flexibility and tunability and the use of bulky optics. These factors lead to the complexity of the optical systems. This paper presents what we believe is a novel approach to generating Bessel beams by utilizing a fully phase-modulated all-dielectric metasurface. The proposed method enables the arbitrary and independent manipulation of cross-polarized and co-polarized components, allowing the creation of Bessel beams featuring multiple polarization conversions when subjected to left-handed circularly polarized (LCP) incidence. To demonstrate the versatility and effectiveness of the method, three metasurfaces with distinct characteristics are designed. The simulated generated Bessel beams exhibit qualities including long focal depth, non-diffraction behavior, self-healing capabilities, and polarization conversion, which align with the theoretical predictions. This work presents novel possibilities for effectively generating and multi-functional application of Bessel beams.

Bessel beams are nondiffracting light beams with large depth-of-focus and self-healing properties, making them suitable as a serial beam writing tool over surfaces with arbitrary topography. This property breaks the inherent resolution vs. depth-of-focus tradeoff of photolithography. One approach for their formation is to use circularly symmetric diffraction gratings. Such a ring grating was designed and fabricated for the extreme ultraviolet (EUV) wavelength of 13.5 nm, a candidate wavelength for future industrial lithography. Exposure of the aerial images showed that a Bessel beam with an approximately 1 mm long z-invariant central core of 223 nm diameter had been achieved, in good agreement with theory. Arbitrary patterns were written using the Bessel spot, demonstrating possible future application of Bessel beams for serial beam writing. Lithographic marks of ~30 nm size were also observed using a high resolution Bessel beam.

The optical binding force (BF) of stratified chiral particles induced by Bessel beam is computed by using the Generalized Lorenz Mie theory. The axial intensity profile of such non-diffracting beams can suppress the influence of the axial intensity which then depended on the interactions between inter-particles. The arbitrarily polarized high order Bessel beam (HOBB) is described in terms of beam shape coefficients (BSCs) within the framework of generalized Lorenz-Mie theories (GLMT). We discuss the influence of the beam half-conical angles and chirality parameter in detail. Different illuminating Bessel beams with arbitrary polarizations are considered, and the corresponding BFs are analyzed. It is shown that the optical BF of stratified chiral spheres can be significantly depending on the incident beam polarizations and the interacting chiral particles handedness. In binding stratified chiral spheres, the out-layered chirality of the stratified chiral spheres should be chosen in accordance with the incident polarizations. This finding may give a recipe to understand the physical mechanism of interactions between multiple chiral stratified particles by using the analytical approach, which plays an important role in manipulating complex multi-layered chiral structures self-arrangement.

Bessel beam, known to have an amplitude that follows a Bessel function of the first kind has attracted considerable attention these last decades, especially due to their propriety of being non-diffractive beam over short distances. In this paper, we propose to generate and control Bessel beams by using a reconfigurable metasurface. This structure allows both to reconfigure the operating frequency and to change the spatial position of the generated Bessel beam. Both numerical simulations and experimental measurements are performed at microwave frequencies to validate the concept.

In this study, we have generated a femtosecond (fs), non-diffracting Bessel beam (800 nm, 1 kHz, 50 fs) of zeroth order through an axicon (IR range, 100, AR coated). We have performed laser ablation of a bimetallic alloy (50% gold, 50 % silver) in the air engaging the generated fs Bessel beam. The high-intensity Bessel beam-matter interaction resulted in the fabrication of exotic bimetallic nanostructures. Extensive field emission scanning electron microscope and atomic force microscopy characterizations were undertaken to study the nanoscale topographical formations. The fs Bessel beam-induced ablation on the alloy target, involving the beam profile imprint on a single surface spot, followed by overlapping two ablation zones, has been meticulously explored. The central lobe ablated area, along with concentric rings-ablated exotic patterns, were thoroughly investigated in the topographical characterization. In the case of the complete raster scan ablation, ladder-like periodic surface structures (with sub ~20 nm growths on the ladder steps) were observed. Energy-dispersive X-ray mapping was performed to confirm the elemental distribution in the nanostructured areas. Subsequently, these plasmonic nanostructures were utilized as surface-enhanced Raman scattering (SERS) platforms to detect traces of real-time explosives, ammonium nitrate (AN), and Tetryl (TL). The SERS spectra of AN depicted a signature Raman peak at 1043 cm^-1, whereas TL exhibited a signature peak near 1353 cm^-1. The lowest possible detected traces were 10 μM and 5 μM, for AN and TL, respectively.

The peculiarities have been studied of acoustooptic (AO) diffraction of quasi-nondiffracting vector Bessel light beams (BLB) on the ultrasound waves in optical gyrotropic cubic crystals.The system of coupled equations describing the process of acoustooptic interaction is solved, diffraction efficiency has been calculated.The mathematical description of AO interaction, which differs from the similar description for the plane optical waves means of two types of synchronism, is conducted.It is shown that besides the usual longitudinal synchronism realized at the equality of phase velocities transmitted and diffracted waves, for Bessel beams it is also necessary to perform the so-called transverse synchronism.It is related with the fact, that Bessel beams with differing cone angles have different spatial structure and, consequently, various values of overlap integral with the input beam.The possibility has been investigated of transformation of the order of phase dislocation of Bessel beams wave front due to AO diffraction.It is proposed to use the process of acoustooptic diffraction in gyrotropic cubic crystals as a method for dynamic manipulation of polarization state of output Bessel beam, particularly for transformation of left-to right (and vice versa) polarization states.

Ideal Bessel beam is a non-diffracting beam and the most attractive property of such beam is non-diffracting propagation. In optics, although the comparisons of maximum propagation distance had been done between Bessel and Gaussian beams by Durnin and Sprangle, respectively, their comparison results are conflict result from their different criteria. It is necessary and significant that the comparison is carried out at microwave band. In this paper, we therefore propose a relatively objective and just comparison criterion at millimeter wavelength, and numerical simulation results and a new conclusion are presented.

In this paper, the self-reconstruction property of astigmatic Bessel beam is studied experimentally and theoretically. Based on the Fresnel diffraction integral theory and Babinet principle, the general expression of the intensity distribution of astigmatic Bessel beams passing through a circular obstacle is derived. The cross-section light intensity at transmission distance of, 10, 30, and 80 mm after astigmatism of the astigmatic Bessel beam are occluded by circular obstacles. The self-reconstruction process of the light field is observed and verified by using an specially designed experimental setup. In the experiment, we choose He-Ne laser as a light source, collimate and expand the beam through a telescope system, and a zero-order astigmatic Bessel beam is generated by a beam vertically incident on the tilted axicon after the diaphragm. A circular obstacle with a radius of 0.2 mm is placed at a distance of 200 mm behind the axicon. Finally, the cross-section intensities at different distances are observed and recorded by a microscope. The experimental phenomena are in good agreement with the theoretical prediction. The results show that the reconstruction of the zero-order astigmatic Bessel beams will occur after passing through the on-axis and off-axis obstacles. And as the transmission distance increases, the outer contour size of the astigmatic Bessel beam becomes larger, and the number of central spot arrays increases, and the complete beam is gradually reconstructed. Particularly, this feature is different from the behavior of the non-diffracting Bessel beam, which maintains the light field unchanged during transmission and has a single central spot. It is expected to be applied to multi-layer multi-particle control. And a new optical property is discovered in the experiments: the reconstruction speed of the beam in the horizontal and vertical direction are not consistent in the reconstruction process, and there is a certain speed difference. Further, we add a spiral phase plate between the diaphragm and the axicon to produce a high-order astigmatic Bessel beam. And it is verified that the high-order astigmatism Bessel beam has the same self-reconstruction characteristics after being shielded by obstacles. Compared with the zero-order aperture system, the high-order beam can not only expand the operating range, but also use the orbital angular momentum carried by the beam to achieve light rotation, which makes the particle manipulation more flexible. The research proves the self-reconstruction characteristics of astigmatic Bessel beams theoretically and experimentally, and broadens the research range of astigmatic Bessel beams. The research results have practical significance and application value in the field of optical micro-manipulation.

In this paper, we have performed experimental, analytical, and numerical studies of beams with topological charges of $\ifmmode\pm\else\textpm\fi{}1$ and $\ifmmode\pm\else\textpm\fi{}2$ formed by silicon binary phase axicons (BPAs) with spiral zone structures. The axicons were illuminated with the Novosibirsk free electron laser radiation (a continuous stream of 100-ps pulses at $f=5.6$ MHz). The cw power of the beams produced reached 30 W and can by doubled via antireflection coating of the axicons. The intensity distribution in the beam cross sections was in good agreement with the Bessel functions and was kept constant within a distance of about $L/r\ensuremath{\approx}190$ and 100, where the first ring radii of the beams r were 0.9 and 1.5 mm for the Bessel beams of the first and second orders, respectively. Although the characteristics of the beams (Bessel cross section, ``diffraction-free'' propagation, self-recovery after passing obstacles, and randomly inhomogeneous media) corresponded to the properties of ideal Bessel beams, their spatial Fourier spectrum (the image in the focal plane of the lens) was, instead of an ideal ring, intertwined segments of arcs with phases shifted by $\ensuremath{\pi}$, the number of which was equal to the double value of the topological charge. This feature can be used, for example, in a demultiplexing unit of a free vortex-wave communication system or for identification of beam topological charge. We also revisited Young's double-slit diffraction and rotation of beams obstructed by a half-plane, previously applied to Laguerre-Gaussian beam characterization, in the case of the Bessel beams. The Young diffraction pattern demonstrated in this case a complicated intensity-phase distribution. It was shown that the Bessel beams formed by BPAs have two important advantages, which can be used in applications, in comparison with other methods of generation, e.g., a combination of an axicon lens with a spiral phase plate. Although the phase jumps of the axicons are designed for a determined wavelength (141 $\ensuremath{\mu}\mathrm{m}$ in our case), the BPAs can form the beams at incident radiation with any wavelength, albeit with a reduced diffraction efficiency, and their cross section is the same for any wavelength.

This work investigates the propagation of solitons in two-dimensional networks created with arrays of mutually incoherent parallel Bessel beams in Kerr-type nonlinear media. Each of the Bessel beams forming the network induces a well-pronounced guiding channel that overlaps with its neighbors through slowly decaying tails.

Due to reduced thermal effects, tightly focused femtosecond laser beams can yield submicron resolution with minimal side effects. In laser direct writing applications, diffraction-free nature of the Bessel beams relaxes alignment of the sample and shortens the production time. Micron-sized central spots and long depth of focused beams can be simultaneously produced. We apply fs Bessel beam single-pulse ablation method to transparent conductive oxide films. We use laser of 1030 nm wavelength and two different axicons (base angles are 25° and 40°). Fabricated structures are characterized by optical microscope, atomic force microscope and scanning electron microscope. Laser beam shaping and virtues of non-diffracted Bessel beams provide periodic structures for scribing in the solar cells or high-resolution displays and reduce the process time.

The advent of wireless communications technology, human connection and collaborations now span countries, continents, and even planets. Despite these advances, however, today's wireless technology still experiences limitations. In the past two decades, terahertz (THz) communications have been researched in depth, and it has become clear that THz communications will be part of expanding the capabilities of wireless technology. Although there was once a substantial gap in knowledge as well as transmission and reception capabilities at THz frequencies, this gap has been steadily closing. Some challenges, still remain; namely, the need to characterize and design for near-field propagation as well as the ability to take advantage of spatial diversity despite the primarily line-of-sight channel. In this proposal, these challenges begin to be addressed. The sub-THz MIMO channel is characterized using a novel channel-sounding implementation, and then a practical physical layer implementation to take advantage of the spatial diversity of the MIMO channel is presented. Then, a research roadmap for enabling broadband, mobile THz communications in the near-field followed by experimental results that characterize the near-field propagation characteristics with both Gaussian and non-diffracting Bessel beams. The performance of Bessel beams are further explored for sub-THz communications in the presence of blockage and shown to be a viable option for broadband, near-field communications. Other wavefront engineering techniques to enable line-of-sight MIMO using orbital angular momentum are discussed from a physical-layer-security perspective, and a novel successive-interference-cancellation eavesdropping attack is proposed along with a potential counter measure. Finally, concluding remarks are given. --Author's abstract

In recent years, much attention has been paid to the parametric characterization of laser beams based on the irradiance moments. Thus, many parameters and factors have been introduced to describe different laser beams in practice. Of them, we found the M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factor which is useful to predict the laser beam quality [1, 2]. And the kurtosis parameter K which is useful to describe the degree of flatness (or sharpness) of laser beam irradiance distribution [2, 3]. While the M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factor is invariant for beam propagating through any paraxial optical system, the kurtosis parameter depends on the axial coordinate along the beam axis z except for a few beams, for example fundamental Gaussian beams and Hermite-Gaussian beams. The M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factor is written in terms of second-irradiance moments and the kurtosis is written in terms of second- and fourth-irradiance moments. In the present contribution, we project to calculate M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> factor of truncated MGBs. Also, we use the propagation equation of non-truncated Mathieu-Gauss beams (MGBs) [4] through paraxial optical system to study the propagation of kurtosis parameter of these beams in polar coordinate. In this work, we adopt the expansion of MGBs in terms of Bessel-Gauss beams (BGBs) to calculate the irradiance moments. Finally, some numerical calculations are performed and discussions are given.