Tunable Beam Research Articles

Liquid crystal-based polarization-dependent, electrically tunable beam deflectors formed via single-step photopolymerization-induced phase separation.

Compared to mechanical ones, liquid crystal (LC) beam deflectors present several advantages, such as non-mechanical control, compactness, and low power consumption, making them a viable alternative. In this work, we demonstrate an LC-based polarization-dependent, electrically tunable beam deflector, which is a composite blazed grating fabricated using a single-step photopolymerization-induced phase separation (PIPS) technique. We investigated the effect of different factors on the performance of the deflector, including the thickness of the upper substrate, the grating period, and the cell gap. The prepared sample demonstrated a diffraction angle of 2°6', and a diffraction efficiency of 40.0%. Unlike previous ones, our proposed fabrication technique for the LC beam deflector provides many benefits, such as simplicity, cost-effectiveness, and large-area production.

Controlled generation of cylindrical vector vortex beams using an optically active material.

An efficient method for the generation of tunable cylindrical vector vortex beams is proposed and demonstrated experimentally using an optically active (OA) material. The uniqueness of the proposed methodology lies in the control over the tunability of the cylindrical vector vortex beams using different concentrations of the optically active material. The efficiency of the generated beams is enhanced by using a single low oblique incidence angle of the input beam on a spatial light modulator with a single-phase profile. Two global parameters are measured experimentally to show the quantitative tunability and efficiency of the generated beams. The proposed method can find applications in the fabrication of various kinds of spiral nanostructures.

Terahertz switchable vortex beam generator based on vanadium dioxide reflective metasurface

Vortex beams exhibit significant potential for applications in diverse fields, such as optical communications, particle manipulation, and quantum information, due to the orbital angular momentum (OAM) they carry. While substantial progress has been made in the generation of vortex beams and the control of their wavefronts, further optimization is necessary to enhance the variability of OAM modes and the modulation of focusing. This study presents three tunable vortex beam generators based on vanadium dioxide metasurfaces. By leveraging the insulator-metal phase transition of vanadium dioxide (VO2), these metasurfaces can convert incident left-circularly polarized (LCP) light into a deflected vortex beam with adjustable OAM modes, a switchable focused vortex beam, or a focused vortex beam with tunable OAM modes in the terahertz band. Specifically, by varying the angle of the incident light, a vortex beam carrying variable topological charges can be deflected over a range from -34° to 90°. Vortex beams with a topological charge of 1 enable reversible switching between near-focus (0.85 mm) and far-focus (3.2 mm), demonstrating highly effective tunable focusing capabilities. Additionally, focused vortex generators with switchable topological charges are proposed. Focused vortex beams with a topological charge of -1 are generated in the insulating state, while a topological charge of -2 is observed in the metallic state. These vortex beam generators allow for different phase gradient distributions in the phase transition states, enabling diverse OAM and variable focuses. This research has potential applications in areas such as dynamic imaging and optical communications.

Terahertz single/dual beam scanning with tunable field of view by cascaded metasurfaces

Dynamic beam scanning with a dynamically tunable beam number, beam direction, and beam polarization remains a challenge in the terahertz gap, which is urgently needed for terahertz radar, next-generation wireless communication, and imaging applications. Different from programmable metasurfaces with element-level phase control, the beam direction is dynamically controlled by two cascaded all-dielectric metasurfaces during in-plane rotation. For a pair of circularly polarized beams with opposite handedness, the scanning field of view (FOV) can be the same or different according to the independent phase modulation in both layers and for both polarization states. Switchable single-beam and dual-beam scanning is achieved by controlling the incident polarization, which covers the ±60° FOV at 0.291 THz with an angular step of 1° and an average gain of 16.2 dBi. The output beam is quasi-circular polarized with an average ellipticity of 0.83. Single beam scanning along a Fibonacci spiral trajectory and dual beam scanning along symmetric and asymmetric trajectories are experimentally validated. Different beam scanning processes are recorded using a terahertz camera, which show good agreement with the theoretical prediction. The wide field-of-view continuous beam scanning with a switchable number of beams and a flexible FOV may have a significant impact on the development of terahertz radar and terahertz intelligent antennas.

Infrared routing and switching with tunable spectral bandwidth using arrays of metallic nanoantennas.

We study infrared routing and switching with tunable spectral bandwidth using in-plane scattering of light by flat Au nanoantenna arrays. The base dimensions of these nanoantennas are approximately 250 by 850 nm, while their heights vary from 20 to 150 nm. Our results show that, with the increase in height, the arrays become more efficient scatterers while their spectra broaden within the 1-1.6 $\mu$m range. Our findings demonstrate that such processes strongly depend on the incident light polarization. For a given polarization, the incident light is efficiently scattered in only two opposite directions along the plane of the arrays, with insignificant transmission. Switching such a polarization by 90$^\circ$, however, suppresses this process, allowing the light to mostly pass through the arrays with minimal scattering. These unique characteristics suggest a tunable beam splitter application in the 1-1.6 $\mu$m range and even longer wavelengths.

Silicon Optrode with a Micromirror‐Tip Providing Tunable Beam Profile During Infrared Neuromodulation of the Rat Neocortex

AbstractInfrared (IR) neuromodulation holds an increasing potential in brain research, which is fueled by novel neuroengineering approaches facilitating the exploration of the biophysical mechanism in the microscale. The group lays down the fundamentals of spatially controlled optical manipulation of inherently temperature‐sensitive neuronal populations. The concept and in vivo validation of a multifunctional, optical stimulation microdevice is presented, which expands the capabilities of conventional optrodes by coupling IR light through a monolithically integrated parabolic micromirror. Heat distribution in the irradiated volume is experimentally analyzed, and the performance of the integrated electrophysiological recording components of the device is tested in the neocortex of anesthetized rodents. Evoked single‐cell responses upon IR irradiation through the novel microtool are evaluated in multiple trials. The safe operation of the implanted device is also presented using immunohistological methods. The results confirm that shift in temperature distribution in the vicinity of the optrode tip can be controlled by the integrated photonic components, and in parallel with the optical stimulation, the device is suitable to interrogate the evoked electrophysiological activity at the single neuron level. The customizable and scalable optrode system provides a new pathway to tailor the location of the heat maximum during infrared neural stimulation.

Phase-tuned acousto-optic spatial filter.

An acousto-optic (AO) tunable filter with a phase-controlled dual-section piezoelectric transducer is designed and created for laser beam shaping (LBS). Owing to the acoustic beam steering effect, we experimentally observe splitting of the two-dimensional transfer function. As a result, we demonstrate generation of tunable bottle laser beams and dual-ring intensity distributions for the diffracted beam.

Topological Directional Coupler

AbstractInterferometers and beam splitters are fundamental building blocks for photonic neuromorphic and quantum computing machinery. In waveguide‐based photonic integrated circuits, beam‐splitting is achieved with directional couplers that rely on transition regions where the waveguides are adiabatically bent to suppress back‐reflection. In this study, a novel, compact approach for introducing guided mode coupling is presented. Along the multimodal domain wall between topological photonic crystals, the photonic spin is conserved to suppress back‐reflection, and the topological protection of the valley degree of freedom is relaxed to implement tunable beam splitting. Rapid advancements in chip‐scale topological photonics suggest that the proposed simultaneous utilization of multiple topological degrees of freedom could benefit the development of novel photonic computing platforms.

Conceptual design of a macromolecular diffractometer for the Jülich high brilliance source.

In this work, a concept for a neutron diffractometer for high-resolution macromolecular structures has been developed within the Jülich High Brilliance Neutron Source (HBS) project. The SELENE optics are adapted to the requirements of the instrument to achieve a tunable low background neutron beam at mm2 scale sample area. With the optimized guide geometry, a low background neutron beam can be achieved at the small sample area with tunable divergence and size. For the 1 × 1mm2 sample, a flux of 1.10 × 107 n/s/cm2 for 0.38° divergence is calculated in the 2-4Å wavelength range, which is about 84.6% of the flux at MaNDi of the high-power spallation source SNS at ORNL. Virtual neutron scattering experiments have been performed to demonstrate the instrument's capabilities for studies of mm scale samples with large unit cells. Results of Vitesse simulations indicate that unit cell sizes of up to 200Å are possible to be resolved with the proposed instrument.

Dynamic Transition from Branched Flow of Light to Beam Steering in Disordered Nematic Liquid Crystal

AbstractOrientational ordered soft matter possessing diverse microstructures has become a focal point of scientific research and technological exploration, thanks to its advancements in serving as an indispensable optical platform enabling propagation of light with multidimensional and manipulatable states. Herein, a facile way is developed to manipulate the in‐plane light beam transition dynamics by harnessing a time‐variable nematic liquid crystal (NLC) film through the electrical‐field‐induced topological defects. The results show that the dynamic change of optical branched flow is associated with the growth in the correlation length of optical potential and the reduction in the density of topological defects. The optical branching can continuously transform to deterministic and tunable beam steering at the low‐defect‐density regime through annihilation kinetics of defects. The explored soft matter system provides an excellent planar platform for the fundamental physics of light interacting with topological defects and may offer new perspectives for novel optics elements toward the applications of soft matter photonics.

Theoretical realization of tunable hollow beams using a periodical ring structure with a complex phase

Hollow beam is a peculiar structure beam, which has been widely used in various areas. Here, we propose a novel diffraction optical element to generate tunable hollow beams. This element is composed of periodic concentric rings. The phase of each ring is periodically distributed between −π and π and satisfies a complex variable function. By tuning the parameters of the structure, we can flexibly manipulate the size and length of the hollow beam. The length of the beam can be increased from 98 λ to 248 λ, and the full width at half maximum varies from 0.43 λ to 0.61 λ. Moreover, the light intensity and side lobe of the hollow beam can also be regulated using the designed diffraction optical element. The potential applications of this highly tunable hollow beam include optical nanomanipulation, microscopic imaging, and nanolithography.

High transmission efficiency collection system for laser-accelerated proton beams based on permanent magnet quadrupoles prefocusing

A new high transmission efficiency, easily tunable, and cost-effective beam collection system is proposed for laser-accelerated proton beams with large divergence angles and wide energy spectra. In previous experiments conducted at the compact laser plasma accelerator platform of Peking University, a beamline was initially constructed with a collection system based on an electromagnetic quadrupoles (EMQs) triplet. However, due to the limited acceptance angle, the EMQs exhibited a monoenergetic transmission efficiency of only 10% to 20% for laser accelerated proton beams. Permanent magnet quadrupoles (PMQs), known for their high magnetic field gradients, compact size, and lower expenses, are well suited for integration with other readily adjustable transmission elements like EMQs and solenoids, effectively enhancing the beam collection capabilities of the system. In this paper, we show that by introducing a pair of centimeter-sized PMQs in front of the EMQs for beam prefocusing, the beam’s transverse size is quickly compressed, enabling transmission of highly divergent protons. Experimental results demonstrate that the prefocusing by PMQs increased the system’s transmission efficiency by a factor of 2.44 to 6.01 compared to the original setup, while also enhancing the energy selection based on stronger chromatic effect. This method can be extended to 100 MeV high-energy proton beamlines and is crucial for applications of laser plasma accelerators. Published by the American Physical Society 2024

Nonvolatile Phase-Only Transmissive Spatial Light Modulator with Electrical Addressability of Individual Pixels.

Active metasurfaces with tunable subwavelength-scale nanoscatterers are promising platforms for high-performance spatial light modulators (SLMs). Among the tuning methods, phase-change materials (PCMs) are attractive because of their nonvolatile, threshold-driven, and drastic optical modulation, rendering zero-static power, crosstalk immunity, and compact pixels. However, current electrically controlled PCM-based metasurfaces are limited to global amplitude modulation, which is insufficient for SLMs. Here, an individual-pixel addressable, transmissive metasurface is experimentally demonstrated using the low-loss PCM Sb2Se3 and doped silicon nanowire heaters. The nanowires simultaneously form a diatomic metasurface, supporting a high-quality-factor (∼406) quasi-bound-state-in-the-continuum mode. A global phase-only modulation of ∼0.25π (∼0.2π) in simulation (experiment) is achieved, showing ten times enhancement. A 2π phase shift is further obtained using a guided-mode resonance with enhanced light-Sb2Se3 interaction. Finally, individual-pixel addressability and SLM functionality are demonstrated through deterministic multilevel switching (ten levels) and tunable far-field beam shaping. Our work presents zero-static power transmissive phase-only SLMs, enabled by electrically controlled low-loss PCMs and individual meta-molecule addressable metasurfaces.

Generation of tunable vortex beams from a side-pumped Nd:YAG laser utilizing spot defect mirrors

High-order vortex lasers are important for high angular momentum quantum entanglement and high-resolution spatial detection. However, traditional spatial phase modulation for Gaussian beams have difficulties achieving high-order and continuously adjustable optical vortex output. In this study, a high-order vortex laser output of continuously adjustable topological charges between 1 and 9 was obtained by adjusting the cavity length in a side-pumped Nd:YAG oscillator with circular spot defects of different sizes etched on the surface of the cavity mirror. Its chirality was also controlled by slightly tilting the cavity mirror, and the mode changes under different cavity parameters and the factors limiting the output optical-vortex order in the side-pumping structure were analyzed. In addition, the generation of optical vortex lattice modes with multiple spatially separated OAMs was obtained based on the spot defect method by displacing the cavity mirror.

Enhanced oxygen evolution reaction of 2-dimensional metal-organic frameworks with tunable nitrogen functionalities by ion beam sputtering

Modification of metal–organic frameworks (MOFs) is recently under the spotlight due to their versatile properties and potential applications in electrochemical catalysis. Here, we successfully demonstrate nitrogen doping into the MOF electrocatalyst without noble metals using a facile, tunable ion beam sputtering (IBS) process for the first time and evaluate the role of the incorporated heteroatom. Two-dimensional Ni-naphthalene-2,6-dicarboxylic acid MOF (NiNDC) with large surface area was subjected to nitrogen IBS (NIBS) and exhibited significantly improved performance for oxygen evolution reaction (OER) with a low overpotential of 222 mV at 10 mA cm−2; a Tafel slope of 88 mV dec-1; and over 120 h of stability at 100 mA cm−2. The relationship between the nitrogen functionalities and catalytic activity was elucidated by spectroscopic analysis and electrochemical measurements, i.e., (i) pyridinic N as an electron-withdrawing group that directly enhances the reaction kinetics, (ii) pyrrolic N to stabilize the catalyst and (iii) graphitic N to enhance the electrical conductivity. We found that the electrocatalytic performance was affected by the ratio of the three nitrogen species, which was controllable by the accelerating potential (AP) of NIBS. This study provides insights into the influence of the chemical state of MOF surfaces on catalytic reactions and presents a novel method for effective nitrogen doping.

Optical Stern–Gerlach Effect in Periodically Poled Electro‐Optical Crystals

AbstractThe Stern–Gerlach (SG) effect provided the first direct experimental evidence of the quantization of electron spin. Although some analog SG effects have been proposed in optical systems, finding a perfect optical analog for the SG effect remains a challenge. Here, a novel optical SG effect is demonstrated in periodically poled electro‐optical crystals. Induced by an applied electric field, the principal axes of crystal rock periodically along the propagation direction of light. When the quasi‐phase‐matching condition is satisfied, the electro‐optical coupling process within the periodically poled crystal can be accurately described by the Schrödinger–Pauli equation for spin‐1/2 particles. The output photons can be deflected toward opposite directions according to their intrinsic spin angular momentum (circular polarizations), since the transversely varying duty cycle of crystal arises an effective magnetic‐field gradient. Moreover, the output photons can be separated according to two arbitrary orthogonal polarization states, allowing us to construct high‐speed electro‐optically tunable polarization beam splitters for arbitrary orthogonal polarization states. Therefore, the optical SG effect provides not only a perfect optical analog for the quantum SG effect but also a useful optical element for optics and quantum physics.

Multi-dimensional tunable arbitrary shape beams with engineered axial profile

Bessel beams, as one type of special light field, would significantly do benefit to several applications such as light-sheet microscopy, particle manipulation and free-space optical communications. In this paper, we investigate the generation of multi-dimensional tunable arbitrary shape beams with engineered axial profile based on the superposition of zero-order Bessel beams by designing the angular spectrum, providing a universal method to manipulate arbitrary shape beams in terms of longitudinal intensity, transverse wavevector distribution and transverse field shape. Through angular spectral analysis, we demonstrate the shape-invariant axial engineering of circle, ellipse, parabolic, and epicycloid-shaped beams, as well as shape-variant axial engineering such as self-acceleration, self-rotation, and self-mode conversion, from both theoretical and experimental perspectives. Our work provides a deep insight into the fundamental properties of arbitrary shape light with engineered axial profile and paves new way toward exploiting more dimensions for its future applications.

Electrically Active Terahertz Liquid‐Crystal Metasurface for Polarization Vortex Beam Switching

AbstractPolarized vortex waves have attracted widespread attention in investigations of light–matter interactions and the augmentation of information capacity owing to their distinctive characteristics. Nevertheless, the reconfigurable generation of vector beams, especially at terahertz (THz) frequencies, remains challenging. In this study, a tunable THz polarization vortex beam generator based on a liquid‐crystal metasurface is proposed. A unit cell featuring reconfigurable linear polarization selectivity is developed. A general methodology for designing metasurfaces to generate customized and reconfigurable polarization patterns is introduced. Furthermore, the electrically tunable generation of polarized patterns and cylinder vector beams is experimentally demonstrated. The findings of this study can open up opportunities for wireless communication and super‐resolution imaging applications.

Development of magnesium alloys: Advanced characterization using synchrotron radiation techniques

Magnesium alloys are the lightest metal structural materials owing to their excellent physical and chemical properties. Microstructural evolution in magnesium alloys under the conditions of casting, thermal-mechanical processing, and in-service environment, play an important role in governing their mechanical properties and reliability/sustainability. A synchrotron light source produces high flux, tunable X-ray energy, high resolution, and high coherence X-ray beams, which can realize in-situ dynamic observation of microstructural evolution in a wide range of alloys during the entire processing chain and in simulated service environments. This article reviews the fundamentals of synchrotron radiation characterization techniques (imaging, diffraction, scattering, and fluorescence holography) and state-of-the-art advanced synchrotron characterization techniques on the microstructure evolution mechanism of magnesium alloys. Case studies span a broad range of solidification, deformation, precipitation, fracture and damage, corrosion, and energy storage. Research opportunities and challenges of physical metallurgy studies of magnesium alloys are highlighted for future studies.

Ultrahigh-brightness 50 MeV electron beam generation from laser wakefield acceleration in a weakly nonlinear regime

We propose an efficient scheme to produce ultrahigh-brightness tens of MeV electron beams by designing a density-tailored plasma to induce a wakefield in the weakly nonlinear regime with a moderate laser energy of 120 mJ. In this scheme, the second bucket of the wakefield can have a much lower phase velocity at the steep plasma density down-ramp than the first bucket and can be exploited to implement longitudinal electron injection at a lower laser intensity, leading to the generation of bright electron beams with ultralow emittance together with low energy spread. Three-dimensional particle-in-cell simulations are carried out and demonstrate that high-quality electron beams with a peak energy of 50 MeV, ultralow emittance of ∼28 nm rad, energy spread of 1%, charge of 4.4 pC, and short duration less than 5 fs can be obtained within a 1-mm-long tailored plasma density, resulting in an ultrahigh six-dimensional brightness B6D,n of ∼2 × 1017 A/m2/0.1%. By changing the density parameters, tunable bright electron beams with peak energies ranging from 5 to 70 MeV, a small emittance of ≤0.1 mm mrad, and a low energy spread at a few-percent level can be obtained. These bright MeV-class electron beams have a variety of potential applications, for example, as ultrafast electron probes for diffraction and imaging, in laboratory astrophysics, in coherent radiation source generation, and as injectors for GeV particle accelerators.