Beam Shaping Applications Research Articles

Shaping 3D diffraction patterns with a binary aperture

In this Letter, we report an approach for the inverse design of binary apertures to generate desired three-dimensional (3D) diffraction patterns in free space. The approach relies on an optimal accumulation algorithm, aiming to determine the distribution of the binary aperture for 3D target patterns in the regime of Fresnel diffraction. This algorithm features high fidelity for complex inverse design compared with conventional iterative algorithms. To demonstrate the validity of our method, various 2D and 3D patterns are chosen and generated using a digital micromirror device that serves as a reconfigurable binary aperture. Experimentally, the generated diffraction patterns exhibit high fidelity with respect to the target ones, achieving an averaged Pearson correlation coefficient of 0.90 for 2D patterns and 0.87 for 3D patterns, respectively. Our work may find applications in laser beam shaping, structured light illumination, and diffractive optical elements.

Orbital angular momentum and rotational properties of off-axis vortex beams in two-dimensional media with anisotropic nonlocal nonlinearity.

By introducing anisotropy into nonlinear propagations, off-axis vortex beams exhibit significantly different characteristics compared to the isotropic case. The orbital angular momentum (OAM) is non-conservative and can periodically change between positive and negative values. Accordingly, the rotation of phase singularity can transit between clockwise and counterclockwise directions. Furthermore, the phase singularity can move to infinity when the OAM approaches zero. By using the Ehrenfest theorem, the motion of the beam center is obtained. Its trajectory can be circular and parabolic or follow other complex shapes, depending closely on the anisotropy of the nonlinearity. The rotational velocity of the beam center can be modulated by the nonlinearity anisotropy and can far exceed the initial value during its propagation. These results may find potential applications in beam shaping and optical manipulation.

A Review on Laser Beam Shaping Application in Laser Powder Bed Fusion

Laser powder bed fusion (L‐PBF) is extensively adopted in the aerospace and automobile industries for producing metallic components. The L‐PBF process involves rapid melting and solidification of metallic powders using a laser source to produce dense parts. Most industrial L‐PBF systems use a fiber‐based laser source that emits a Gaussian beam distribution. However, the conventional Gaussian beam used in L‐PBF processes presents inherent limitations that can impact the quality and properties of the final products. This review aims to provide a theoretical background of laser beam shaping techniques and explores the application of alternative beam shapes in L‐PBF. It investigates how different beam profiles affect the melt pool geometry, process stability, productivity, mechanical properties, microstructure, and surface roughness of fabricated parts. Additionally, it discusses different types of beam‐shaping techniques and elements utilized to generate distinct beam shapes. Furthermore, different constraints and limitations that hinder the full exploitation of beam shaping are critically discussed. By analyzing the impact of beam shaping in L‐PBF, this review provides insight into optimizing the AM process, enhancing part quality, and improving processing performance. It will also help readers to overview the research gaps, challenges, and promising future directions in laser beam shaping applications in L‐PBF.This review comprehensively covers and presents the current research trend of laser beam shaping applications in L‐PBF. It delves into the opportunities, challenges, limitations, and futures prospects of beam shaping applications. Furthermore, presents the methods and techniques used to modulate the laser beam profile, including spatial and temporal.This article is protected by copyright. All rights reserved.

Control of non-Hermitian skin effect by staggered synthetic gauge fields

Synthetic gauge fields introduce an unconventional degree of freedom for studying many fundamental phenomena in different branches of physics. Here, we propose a scheme to use staggered synthetic gauge fields for control of the non-Hermitian skin effect (NHSE). A modified Su–Schrieffer–Heeger model is employed, where two dimer chains with non-reciprocal coupling phases are coupled, exhibiting non-trivial point-gap topology and the NHSE. In contrast to previous studies, the skin modes in our model are solely determined by the coupling phase terms associated with the staggered synthetic gauge fields. By manipulating such gauge fields, we can achieve maneuvering of skin modes as well as the bipolar NHSE. As a typical example, we set up a domain wall by imposing different synthetic gauge fields on two sides of the wall, thereby demonstrating flexible control of the non-Hermitian skin modes at the domain wall. Our scheme opens a new avenue for the creation and manipulation of NHSE by synthetic gauge fields, which may find applications in beam shaping and non-Hermitian topological devices.

Graphene-Tuned, Tightly Coupled Hybrid Plasmonic Meta-Atoms.

Tightly coupled meta-atoms (TCMAs) are densely packed metamaterials with unnatural refractive indexes. Actively modulated TCMAs with tunable optical properties have found many applications in beam shaping, holography, and enhanced light-matter interactions. Typically, TCMAs are studied in the classic Bloch theory. Here, tightly coupled H-shaped meta-atoms are proposed with an ultra-high permittivity of ~6000, and their active modulation with graphene is designed by using the tightly coupled dipole array (TCDA) theory. The H-shaped meta-atoms are used as dipole arms, and the graphene strips function as the dipole loads. By tuning the chemical potential of graphene, the resonant amplitude, frequency, and permittivity are dynamically modulated. The simulations indicate that the real and imaginary parts of permittivity change from 6854 to 1522 and from 7356 to 2870, respectively. The experimental validation demonstrates a modulation depth of 11.6% in the resonant frequency, i.e., from 219.4 to 195 GHz, and a substantial 52.5% modulation depth in transmittance under a bias voltage of less than 1.5 V.

Polychromatic photonic Floquet-Bloch oscillations.

Photonic Floquet-Bloch oscillations (FBOs), a new type of Bloch-like oscillations in photonic Floquet lattices, have recently been observed as a typical discrete self-imaging effect. Here, we theoretically investigate the spectral range of approximate photonic Floquet-Bloch oscillations in arrays of evanescently coupled optical waveguides and show the adjustability of the spectral range. At an appropriate amplitude of the Floquet modulation, we have demonstrated approximate photonic FBOs over a broad spectral range, termed "polychromatic photonic Floquet-Bloch oscillations," which manifest as approximate self-imaging of polychromatic beams. Furthermore, by designing the functional form of the Floquet modulation, we can cascade two polychromatic photonic FBOs and further enhance the performance of polychromatic self-imaging. Our results provide a simple and novel mechanism for achieving polychromatic self-imaging in waveguide arrays and may find applications in polychromatic beam shaping and broadband optical signal processing.

Spatially nonuniformly correlated vortex beams and their arrays

We introduce a class of partially coherent sources with spatially nonuniformly correlation properties and an off-axis helicoidal phase. It is shown that the unique correlation and phase properties of such sources lead to radiated fields with extraordinary propagation characteristics, such as dark hollow with zero central intensity, self-focusing and lateral self-shifting light intensity. Based on such novel random sources, two types of nonuniformly correlated vortex beam arrays with radial and rectangular symmetry are explored. Analytical and numerical investigations for the evolutions of such light fields are made by the model decomposition representation of correlation function and fast Fourier transform method. The results demonstrate new opportunities for modeling off-axis self-focusing vortex beams and other beam shaping applications by joint modulation of coherence and phase.

Immersion laser separation: Enhancing efficiency and quality in cutting irregular lenses

Irregular lenses are commonly employed in various beam shaping, imaging, and other optical applications. They require secondary processing to meet specific design and assembly criteria. Bessel beam lasers have gained popularity for their ability to efficiently separate hard-brittle materials owing to their high processing quality and speed. However, the complex surface of irregular lenses creates challenges such as refraction and scattering, which impede the laser beam’s ability to form a laser center lobe inside the material. This paper proposes an innovative technique called immersion laser separation (ILS), where an irregular lens is immersed in a refractive index matching medium to create a compound with a uniform refractive index. This approach mitigates the impact of surface complexity on the optical path of the Bessel beam. The separation of a fast axis collimator (FAC) by ILS is used as an example to test the proposed technique. The distribution characteristics of the Bessel beam light field inside the lens material under different refractive index were investigated to find that the laser consistently forms a laser center lobe inside the material during cutting when the matching deviation is small. This results in a modified area that covers the entire surface. The maximum cutting speed can reach 50 mm/s, the cutting surface roughness is less than 700 nm, and the technique produces no chips or micro-cracks, ensuring uniformly high-quality separation. Experimental and simulation results are in close agreement, suggesting that the proposed technique is effective for the efficient, high-quality cutting of irregular lenses.

A One-Bit Programmable Multi-Functional Metasurface for Microwave Beam Shaping.

In this paper, we demonstrate a multi-functional metasurface for microwave beam-shaping application. The metasurface consists of an array of programmable unit cells, and each unit cell is integrated with one varactor diode. By turning the electrical bias on the diode on and off, the phase delay of the microwave reflected by the metasurface can be switched between 0 and π at a 6.2 GHz frequency, which makes the metasurface 1-bit-coded. By programming the 1-bit-coded metasurface, the generation of a single-focus beam, a double-focus beam and a focused vortex beam was experimentally demonstrated. Furthermore, the single-focus beam with tunable focal lengths of 54 mm, 103 mm and 152 mm was experimentally observed at 5.7 GHz. The proposed programmable metasurface manifests robust and flexible beam-shaping ability which allows its application to microwave imaging, information transmission and sensing applications.

Orientation-selective elliptic higher-order Poincaré sphere beam arrays

In this study, a new class of light-beam arrays, called orientation-selective elliptic higher-order Poincaré sphere (OS-EHOPS) beam arrays, is introduced as an extension of the scalar case reported in a previous study (Wang et al., 2020). For each beamlet of such beam arrays, the state of polarization represented by higher-/hybrid-order Poincaré spheres is spatially inhomogeneous, whereas the spatial profile takes on an elliptical shape with controllable orientation and ellipticity. The design procedure, which is rooted in multi-coordinate transformations, is comprehensively described and analyzed. Furthermore, we established an experimental setup involving a phase-only spatial light modulator that served as a Dammann grating and a common-path interferometer to effectively generate OS-EHOPS beam arrays. Two types of OS-EHOPS beam arrays, with hexagonal and double-ring-arranged structures, were synthesized to verify the feasibility of our method. Our design and optical system have potential applications in beam shaping and orientation-selective microfabrication.

Laser-Written Tunable Liquid Crystal Aberration Correctors.

In this Article, we present a series of novel laser-written liquid crystal (LC) devices for aberration control for applications in beam shaping or aberration correction through adaptive optics. Each transparent LC device can correct for a chosen aberration mode with continuous greyscale tuning up to a total magnitude of more than 2π radians phase difference peak to peak at a wavelength of λ = 660 nm. For the purpose of demonstration, we present five different devices for the correction of five independent Zernike polynomial modes (although the technique could readily be used to manufacture devices based on other modes). Each device is operated by a single electrode pair tuned between 0 and 10 V. These devices have potential as a low-cost alternative to spatial light modulators for applications where a low-order aberration correction is sufficient and transmissive geometries are required.

Application of ultrafast laser beam shaping in micro-optical elements

The manufacturing and application of micro-optical elements are constantly evolving toward miniaturization, integration, and intelligence and have important applications in holographic displays, optical imaging, laser processing, information processing, and other fields. Ultrafast lasers, with their ultrashort pulse width, extremely high peak power, high processing resolution, small thermal influence zone, and nondestructive material processing advantages, have become an important processing method for preparing micro-optical elements. However, the laser output from the laser usually has a Gaussian distribution, with limitations in spatial and temporal energy and shape distribution, making it difficult to meet the requirements of processing efficiency and quality, which poses new challenges to ultrafast laser manufacturing technology. Therefore, by shaping the ultrafast laser beam and regulating nonlinear optical effects, the optimization and adjustment of the beam shape can be achieved, thus improving the quality and efficiency of micro-optical element processing. Ultrafast laser beam shaping technology provides a new method for the manufacture of micro-optical elements. This article first introduces the commonly used manufacturing methods for micro-optical elements. Second, from the perspective of the temporal domain, spatial domain, and spatiotemporal domain, the basic principles, methods, and existing problems of ultrafast laser beam shaping are summarized. Then, the application of these shaping technologies in the preparation of micro-optical elements is elaborated. Finally, the challenges and future development prospects of ultrafast laser beam shaping technology are discussed.

Programmable freeform optics with extended white light sources: possibilities and limitations.

Freeform optics can be used in lighting applications to generate accurate prescribed illumination patterns from compact light sources such as LEDs. When targeting dynamic illumination systems, a time-variable optical functionality is needed. Phase-only spatial light modulators (SLMs) have been used in the past for various dynamic beam shaping applications with monochromatic, zero-étendue illumination under paraxial conditions. Such limitations can no longer hold when considering lighting applications. In this paper, a novel algorithm for the calculation of smooth phase shift patterns is presented in order to generate arbitrary target patterns from arbitrary incident wave fronts for non-paraxial conditions. When applying such phase shift patterns to SLMs, these devices can be considered as programmable freeform optics. The experimental performance of the calculated phase patterns is analyzed on a real SLM, with a maximal phase shift of 6π, for collimated laser beams and white LEDs. The possibilities and limitations of generating accurate prescribed target patterns are critically discussed in terms of the angular extent of the target pattern, the consider spectrum of the light source and the étendue of the incident light beam.

Thermocapillary Patterning of Highly Uniform Microarrays by Resonant Wavelength Excitation

For decades, researchers have been exploring pattern-forming instabilities in free surface thin films in the hope of developing alternative lithographic techniques for applications only requiring resolution limits in the submicron range. Previous studies have shown how the pitch and shape of elements in an array can be varied by adjusting the magnitude of surface forces and growth time prior to solidification in situ. Since the formations emerge naturally from an initial flat molten film, the final arrays exhibit ultrasmooth interfaces and are therefore ideally suited to beam-shaping applications such as thin-film micro-optics. Progress in this field has stalled, however, due to the very nature of the formation process. Even when great care is taken to ensure that initial films are defect-free, final arrays still exhibit unacceptable variability in pitch, shape, and height due to ubiquitous sources of noise responsible for instability and growth. In this work, we focus on a thermocapillary instability in slender molten films exposed to a very large thermal gradient. We begin with a discussion and demonstration of why this instability inextricably leads to highly disordered arrays even if initialized by a film with very small amplitude surface roughness. We then demonstrate how spatially periodic modulation of the thermal field, implemented in three different ways, can induce synchronous growth of highly uniform periodic arrays despite noisy initial conditions. Results based on linear and weakly nonlinear stability analysis, Bloch wave analysis, and direct numerical simulation of the interface equation reveal how resonant wavelength excitations occurring between the modulation and instability driving fields are responsible for such rapid and coherent growth. An additional benefit is that the modulation field can be selected to yield an array pitch much smaller than in unmodulated systems.

Two-dimensional manipulation of ultraviolet Photonic Spin Hall Effect with high efficiency broadband dielectric metasurface

Photonic Spin Hall Effect (PSHE) is a relativistic spin-orbit coupling phenomenon that can provide a wide range of spin-controlled nano-photon applications. However, most of the research results have been achieved only on 1D modulation of PSHE and the PSHE is very weak because of the extremely small spin-orbit interaction. Here, we propose a novel method to achieve a 2D manipulation of PSHE based on the broadband dielectric metasurface with refractive efficiency of above 80%. Using silicon nitride nanorods with perfect half-wave plates properties, a high-efficiency metasurface is designed, which demonstrated that directly realizes the high-performance PSHE in the ultraviolet region. Moreover, the metasurface can realize longitudinal focusing and transverse deflection of photons in different spin states by using the Pancharatnam-Berry (PB) phase and propagation phase, thus enabling 2D flexible manipulation of spin photons. The results show that the broadband dielectric metasurface offers a method to develop a high-efficiency PSHE for generating and manipulating spin-polarized photons, achieving important applications in optical communication, beam shaping, and optical sensors.

Fractional Fourier transforms of circular cosine-hyperbolic-Gaussian beams

The propagation properties of a circular cosh-Gaussian beam (CiChGB) in a fractional Fourier transform (FRFT) optical system are investigated theoretically. The analytical expressions for a CiChGB propagating through apertured and unapertured FRFT systems are derived based on the Collins formula and the expansion of the hard-aperture function into a finite sum of Gaussian functions. From the obtained expressions, the evolution of the intensity distribution at the output plane is analysed with illustrative numerical examples. It is shown that the intensity distribution of the CiChGB propagating in FRFT is closely dependent on the decentred beam parameter and the aperture size besides the fractional order of the FRFT system. The results obtained may be beneficial to applications in laser beam shaping, optical trapping, and micro-particle manipulation.

Anti-reflection coatings for epsilon-near-zero materials

Epsilon-near-zero (ENZ) materials have attracted much interest within the photonics community due to the various novel light-matter interactions that can occur in the ENZ regime. These materials display a large impedance mismatch between the ENZ material and free space, making it difficult to couple light into the medium at normal incidence. In this article, we demonstrate that enhanced light coupling into an ENZ metamaterial stack can be achieved via the design and fabrication of anti-reflection coatings, which are simple to fabricate via e-beam evaporation. The coating fabricated has been optimized not only to minimize reflection but also aims to maximize transmission — making these designs applicable to e.g. beam shaping applications. We achieve a transmission enhancement of 20% through our metamaterial over a 150 nm range and reflection minimization of 50% over a 200 nm range.

Investigation of partially coherent vector vortex beams with non-isotropic states of spatial correlation.

In this work, the far-field properties of non-isotropic partially coherent vector vortex beams (PCVVBs) are investigated both theoretically and experimentally. The term non-isotropic signifies that the spatial correlations between the parallel and orthogonal electric field components are distinguishable. It is found that self-orientation and shaping of intensity profile, correlation-induced polarization and depolarization are highly dependent on both the non-isotropic correlation parameters and Poincaré-Hopf index (PHI) of the beam. The simultaneous depolarization and polarization effects are due to the difference in the input correlation parameters that alter the state of polarization (SOP) and degree of polarization (DOP) distributions. The experimental results are in good agreement with the theoretical predictions. The distinguishability of correlation parameters at the source plane leads to significant changes on its intensity profile, DOP, and SOP distributions on far-field propagation, which may found potential applications in beam shaping, detecting and imaging atmospheric lidar, optical imaging and directional transportation where the self-rotation characteristic of beam plays an important role.

Effect of spatial variation of the duty cycle in transverse second-harmonic generation.

Transverse second-harmonic generation, in which the emission angles of the second harmonic are determined by the spatial modulation of the quadratic nonlinearity, has important applications in nonlinear optical imaging, holography, and beam shaping. Here we study the role of the local duty cycle of the nonlinearity on the light intensity distribution in transverse second-harmonic generation, taking the generation of perfect vortices in periodically poled ferroelectric crystal as an example. We show, theoretically and experimentally, that spatial variations of the nonlinearity modulation must be accompanied by the corresponding changes of the width of inverted ferroelectric domains, to ensure uniformity of the light intensity distribution in the generated second harmonic. This work provides a fundamental way to achieve high-quality transverse second-harmonic generation and, hence, opens more possibilities in applications based on harmonic generation and its control.

Programmable Manipulations of Terahertz Beams by Graphene-Based Metasurface With Both Amplitude and Phase Modulations

Terahertz metasurface with digital, programmable control recently gained considerable attention for its potential applications in high-speed imaging, nondestructive sensing, and wireless communication. With elaborate design, the metasurface can perform amplitude, phase, and polarization modulations of electromagnetic waves. Most digital programmable metasurfaces focus on only one of the three dimensions. Here, we propose a graphene-based THz metasurface with both phase and amplitude modulations, which consists of an artificially constructed metal-insulator-metal structure and two-dimensional graphene material. Each meta-atom of the metasurface is divided into two sub-atoms, and the two sub-atoms can reflect terahertz waves with a phase difference of 180°. Meanwhile, the amplitude of the sub-atom can be effectively modulated or even switched off by applying different gate voltages to the graphene. By independently controlling the amplitude response of the two sub-atoms, the whole meta-atom can dynamically control both amplitude and phase responses of the cross-polarization waves. By carefully designing the coding patterns, the digital metasurface can control both beam direction and intensity, which may lead to various advanced applications in beam shaping, radar detection systems, and high-quality holography.