Generation Of Bessel Beams Research Articles

Recent Advances in Spatial Self‐Phase Modulation with 2D Materials and its Applications

AbstractIn recent years, spatial self‐phase modulation (SSPM) with two‐dimensional (2D) materials has attracted the attention of many researchers as an emerging and ubiquitous nonlinear optical effect. In this review, the state of the art of 2D material‐based SSPM is summarized. SSPM measures or tunes the nonlinearity of 2D materials, and it is also an effective approach to study the band structure of 2D materials. Several modified forms of SSPM, such as high‐order, white‐light‐excited, vector field excited, and optically nonlinearly enhanced SSPM are also presented. Subsequently, the physical origin of the SSPM formation mechanism is compared and analyzed. Furthermore, the applications of SSPM with 2D materials, including passive photonic devices, generation of Bessel beams, and identifying the mode of the orbital angular momentum, are listed. Finally, several urgent problems of the SSPM with 2D materials, potential applications, and prospects for future development are presented.

Realization of Terahertz Wavefront Manipulation Using Transmission-Type Dielectric Metasurfaces

Metasurfaces, composed of an array of subwavelength artificial structures, have attracted great interest, owing to their high ability in locally manipulating the wavefront of electromagnetic waves. Here, we propose a dielectric metasurface based on a fused silica resonator, consisting of a rectangular-shaped bar placed in the center of a cross net-shaped structure, to manipulate the wavefront of terahertz waves. As proof of concept, several transmission-type devices for spatial modulation are designed at the target frequency of 0.14 THz, including on-axis and off-axis focusing, generation of a non-diffracting Bessel beam, and multi-focus lens. The simulated efficiencies range from 45% to 62%. This novel approach for manipulating THz wavefronts can be also used for information storage and other phase-related techniques in the rapid development of THz applications.

Partitioned gradient-index phononic crystals for full phase control

Gradient-index phononic crystals (GRIN-PC), characterized by layers with spatially changing refractive indices, have recently been investigated as part of the effort to realize flat lenses in acoustic and elastic regimes. Such gradient-index lens must be inversely designed from the corresponding refractive indices in order to manipulate the target wave. Unfortunately, estimating the index of this type of lens is not straightforward and requires substantial iterative computation in general, which greatly limits the applicability of GRIN-PC to flat lenses. In this work, we propose a novel design of a GRIN-PC in which neighboring layers are separated by partitions, thus preventing waves in each layer from interacting with other layers. This partitioned GRIN-PC design enables us readily to control the phase gradient accurately at the lens’ end, resulting in direct calculation of indices for target wave manipulation. A detailed methodology for partitioned GRIN-PC based collimator and Bessel-beam generator is proposed and experimentally validated to confirm the versatile use of our design in wave engineering applications.

Void and micro-crack generation in transparent materials with high-energy first-order vector Bessel beam

In this work, we present efficient generation of a high-quality vector Bessel beam using an S-wave plate (radial/azimuth polarization converter) together with an ordinary glass axicon. We examine laser-induced modifications in glass with different pulse durations. We achieve material cracking and observe dominant crack propagation directions caused by the generated beam’s intensity asymmetry. By translating the beam, we demonstrate potential application of vector Bessel beams and their transverse polarization components for microprocessing of transparent materials using ultra-short pulses.

Wearable Conformal Metasurfaces for Polarization Division Multiplexing

AbstractIn practice, there is a strong requirement for modulating the performance of existing bulk devices without changing their physical geometry. In this study, by attaching a flexible metasurface on a cylindrical lens, a wearable conformal metasurface for terahertz polarization division multiplexing is demonstrated, which could be used in wireless communications, detection, and imaging. The integrated metasurface/lens can achieve the control functions of spot focusing, generation of Bessel beams, and phase holograms, respectively, for crosspolarized waves and line focusing for copolarized waves. A total modulation efficiency of up to 87% is experimentally obtained. Notably, the metasurfaces can be attached on/removed from existing bulk devices multiple times, without reducing the performances of both metasurface and conventional devices. As the flexible samples are fabricated using the cost‐effective standard flexible printed circuit technique, a multilayer conformal metasurface can be easily obtained for an efficient control. Furthermore, the same bulk device can be integrated with different flexible metasurfaces for various controls. Thus, the proposed metasurface can provide a promising flexible platform for various integrated applications and contribute to the development of wearable functional devices.

Polarization and direction-controlled asymmetric multifunctional metadevice for focusing, vortex and Bessel beam generation.

Integrating multiple independent functionalities into one single photonic device has been an important part in optoelectronic system. In this paper, we here propose a kind of asymmetric multifunctional metadevice operating at 1550 nm (in optical communication band), which can manipulate the light with four different functions, depending on the polarization and illumination direction of incident light. As a proof of our concept, we design this metadevice composed of the upper metasurface layer, middle grating layer and lower metasurface layer. For x-polarized incident light, the metadevice under forward illumination works as transmissive focusing lens and vortex beam generator of y-polarized light, while under backward illumination it acts as a reflective vortex beam generator. In contrast, for y-polarized incident light, the metadevice under forward illumination behaves as a reflective Bessel beam generator, while a combination of transmissive vortex beam generator and focusing lens of x-polarized light under backward illumination. Our findings may motivate the realization of high-performance multifunctional metadevices and extend the application in complex integrated optical system.

Generation of second harmonic Bessel beams through hybrid meta-axicons.

Bessel beams are of great potential applications in many fields due to their non-diffraction and self-reconstruction. Here we firstly present a type of nonlinear meta-axicon to generate second harmonic Bessel beams. The nonlinear meta-axicons are based on Au/WS2 hybrid nanostructures. Zero-order and first-order Bessel beams of second harmonic are generated under exciting of 810 nm femtosecond laser. In addition, the performances of the nonlinear meta-axicons, such as the second harmonic generation (SHG) efficiency, non-diffracting distance and full width at half maximum (FWHM) are analyzed theoretically and experimentally. The experimental results are consistent with the predicted, which can enable miniaturized nonlinear optical devices related to generate nonlinear Bessel beams, having potential application in nonlinear optical manipulation, imaging and tractor beams.

Generation of a Bessel beam in FDTD using a cylindrical antenna.

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.

Bessel Beam Generation Using Dielectric Planar Lenses at Millimeter Frequencies

In this work a dielectric planar lens is proposed to generate a Bessel beam. The lens works at Ka-band and produces a non-diffraction range within the Fresnel region of the antenna. The methodology to design the aperture antenna at millimetre or microwave frequencies is presented. It is applied to a dielectric planar lens made up of cells that shapes the radiated near-field by adjusting the unit cell response. An approach based on a second order polynomial is proposed to consider the angular dependence of the phase-shift response of the cell in the designing process. In order to implement the lens physically, two novel cells, based on rectangular and hexagonal prisms, are proposed, and their performance is compared. The cells ensure the index dielectric media variation using airgaps to control the overall density of the material. After fully characterizing the cells, a design is carried out for the two proposed type of cells. The requirement for the Bessel beam is a depth-of-field of 650 mm at 28 GHz. After evaluating the design in a full-wave simulation, both prototypes were manufactured using a 3-D printing technique. Finally, the prototypes were measured in a planar acquisition range to evaluate the performances of the Bessel beam. Both lenses show a good agreement between simulations and measurements, obtaining promising results in the Bessel beam generation by index-graded dielectric lenses at Ka-band.

Subtraction method via phase mask enables contrast enhancement in scanned Bessel light-sheet microscopy.

We report on the generation of a hollow Bessel beam with a hole along the direction of propagation by using an easy-to-implement phase mask and investigate its effectiveness to reduce the out-of-focus background in light-sheet fluorescence microscopy (LSFM) with scanned Bessel beams by subtraction imaging. Overlaying ${\pi }$π-phase retardation between the two equal parts of the Bessel beam across the entrance pupil of the objective lens, a hollow Bessel beam with zero intensity at the focal plane can be achieved. By optimizing the numerical aperture of the annular mask applied in the hollow Bessel beam, matched distributions of the ring system between the hollow Bessel beam and the conventional Bessel beam are achieved. By subtraction between the two LSFM images, the out-of-focus blur caused by the ring system of the Bessel beam can be significantly reduced. Comparison with conventional Bessel LSFM images exhibits a better sectioning capability and higher contrast.

Using Bessel beams and two-photon absorption to predict radiation effects in microelectronics.

Pulsed-laser testing is an attractive tool for studying space-based radiation effects in microelectronics because it provides a high degree of spatial resolution and is more cost-effective than conventional accelerator-based testing. However, quantitatively predicting the effects of radiation is challenging for this optical method. A new approach to pulsed-laser testing is presented, which addresses these challenges by using a Bessel beam and carrier generation via two-photon absorption. By producing a carrier distribution in the device under test that is similar to that of a heavy ion, this optical approach aims to quantitatively predict the response of the device under heavy ion tests that represent space radiation. Furthermore, the carrier distribution can be accurately described using a single analytic expression thereby enabling the laser to be tuned to emulate a specific heavy ion. Herein, we describe the modifications made to an existing pulsed-laser setup to generate this carrier distribution, characterize this distribution using a novel method that provides sub-micron spatial resolution, and provide the equations that describe the distribution. Finally, we use this method to study a silicon photodiode and find that the transient response of the device shows strong agreement with the response generated using heavy ions.

Generation of Bessel beams with 3D‐printed lens

In this article, the 3D-printed dielectric lens is proposed to generate Bessel beam in millimeter-wave band. The dielectric lens is made of many square unit cells with the side length of a half wavelength. The unit cells with different thicknesses generate different insertion phase shift to the transmitted millimeter wave. The insertion phase distribution of the lens is calculated by comparing the phase distributions of the incident Gaussian beam and the desired output Bessel beam. Three types of lenses are simulated and fabricated using 3D printing technology with Nylon. The measured magnitude and phase distributions of zero-order Bessel beam agree with the simulated results very well and the measured phase distributions of the first-order Bessel beam carry orbital angular momentum.

Generation of optical Y-junction Bessel beams.

A method is proposed to split the central spot of zero-order Bessel beams into two parallel spots along the propagation axis of the beam. A magnetic-liquid deformable mirror is used to provide the required phase profile combining an axicon and a phase step. The obtained Y-junction Bessel beam has been characterized; the 80 µm central spot of the Bessel beam is split into two spots of the same size that have been propagated over a length exceeding 15 cm. The observations are consistent with the predictions of a numerical model. Potential applications of Y-junction Bessel beams are discussed.

Phase masks for electron microscopy fabricated by thermal scanning probe lithography

Nano-structured phase masks offer intriguing possibilities in electron-beam shaping. The fabrication of such phase masks is typically achieved by focused (Ga+-)ion beam milling of thin membranes. To overcome the problem of Ga implantation in the phase mask, we explore the fabrication of silicon-nitride phase masks using thermal scanning probe lithography combined with wet and dry etching. The functionality of the phase masks is demonstrated by generation of electron Vortex and Bessel beams. Major benefit of thermal scanning probe lithography in addition to the absence of ion implantation is the high accuracy and control over the patterned structure and depth.

Detecting the Extremely Small Angle of an Axicon by Phase-Shifting Digital Holography

Axicon is an optical element that can be used to produce high-quality Bessel beams efficiently. In general, the smaller the base angle of the axicon is, the longer the diffraction-free distance of the generated Bessel beam will be. Therefore, axicon with an extremely small base angle is important for the generation of Bessel beam. However, the measurement of an extremely small base angle is a challenge. Here, we applied the phase-shifting digital holography in the measurement of axicon angle. The errors of the three measured axicons with base angles of 0.5°, 1°, and 1° were 1.94%, 4.43%, and 1.63%, respectively.

Fabrication of phase masks from amorphous carbon thin films for electron-beam shaping.

Background: Electron-beam shaping opens up the possibility for novel imaging techniques in scanning (transmission) electron microscopy (S(T)EM). Phase-modulating thin-film devices (phase masks) made of amorphous silicon nitride are commonly used to generate a wide range of different beam shapes. An additional conductive layer on such a device is required to avoid charging under electron-beam irradiation, which induces unwanted scattering events.Results: Phase masks of conductive amorphous carbon (aC) were successfully fabricated with optical lithography and focused ion beam milling. Analysis by TEM shows the successful generation of Bessel and vortex beams. No charging or degradation of the aC phase masks was observed.Conclusion: Amorphous carbon can be used as an alternative to silicon nitride for phase masks at the expense of a more complex fabrication process. The quality of arbitrary beam shapes could benefit from the application of phase masks made of amorphous C.

Extremely high-aspect-ratio ultrafast Bessel beam generation and stealth dicing of multi-millimeter thick glass

We report on the development of an ultrafast beam shaper capable of generating Bessel beams of high cone angle that maintain a high intensity hot spot with subwavelength diameter over a propagation distance in excess of 8 mm. This generates a high intensity focal region with extremely high aspect ratio exceeding 10 000:1. The absence of intermediate focusing in the shaper allows for shaping very high energies, up to Joule levels. We demonstrate a proof of principle application of the Bessel beam shaper for stealth dicing of thick glass, up to 1 cm. We expect that this high energy Bessel beam shaper will have applications in several areas of high intensity laser physics.

High-efficiency Bessel beam array generation by Huygens metasurfaces

Abstract Bessel beams have attracted considerable interest because of their unique non-diffractive, self-healing characteristics. Different approaches have been proposed to generate Bessel beams, such as using axicons, diffractive optical elements, composite holograms, or spatial light modulators. However, these approaches have suffered from limited numerical aperture, low efficiency, polarization-dependent properties, etc. Here, by utilizing dielectric Huygens metasurfaces as ultrathin, compact platforms by integrating the functionalities of Dammann gratings and axicons, we successfully demonstrate multiple Bessel beam generation with polarization-independent property. The number of two-dimensional arrays can be controlled flexibly, which can enhance information capacity with a total efficiency that can reach 66.36%. This method can have various applications, such as parallel laser fabrication, efficient optical tweezers, and optical communication.

Application of vector diffraction theory in geometric phase based metasurfaces

In geometric phase based metasurfaces, phase modulation of the output light can be achieved by designing the shape and layout of the subwavelength structure. For traditional electromagnetic simulation software, the operating principle is often based on finite-difference time-domain, finite element method, or finite integration technique (FIT). Their disadvantages include, for example, the time-consuming simulation and the complicated modeling process. In addition, the computational accuracy may be affected by the size of divided grids. In this paper, an improved vector diffraction theory is investigated to calculate the distribution of the transmitted light field when the incident circular polarization light (CPL) passes through the geometric phase based metasurfaces. The structure acts as a diffraction screen when using the method to calculate the diffraction field. When CPL is incident, the geometric phase is imparted to the output light, and the transmission light field is calculated by normal vector diffraction theory. Three kinds of structures, which can be seen as nano-object arrays, have been designed and characterized to validate our method. The first and second devices realized the separation of cross-polarization and co-polarization components, and the third one realized the function of the focusing lens with a subwavelength catenary array. The transmission fields calculated by the refined vector diffraction theory are in good agreement with the FIT method. We believe this simple yet generalized method can be employed for efficient design of geometric phase based metasurfaces, such as Bessel beam generators, focusing lenses, holographic coding, etc.

Highly efficient generation of Bessel beams with polarization insensitive metasurfaces.

We present a generic approach for the generation of pseudo non-diffracting Bessel beams using polarization insensitive metasurfaces with high efficiency. Cascaded unit cells, which are fully symmetric, are designed for the complete 2π phase control in the transmission mode. Based on the topological arrangements of such unit cells, two metasurfaces for the generation of zero-order (i.e., single phase profile) and first-order (i.e., merger of two distinct phase profiles) Bessel beams are designed and characterized. Both numerical simulations and experimental measurements are in agreement with each other, confirming the electromagnetic characteristics of the reported Bessel beams. Owing to the isotropy of the unit cells and the rotational symmetry of the arrangements, the proposed metasurfaces are polarization insensitive, providing a promising avenue for achieving such wave manipulations with any linear or circular polarization.