Achromatic and Coma-Corrected Hybrid Meta-Optics for High-Performance Thermal Imaging.

Long-wave infrared (LWIR) imaging, or thermal imaging, is widely applied in night vision and security monitoring. However, the widespread use of LWIR imagers is impeded by their bulky size, considerable weight, and high cost. While flat meta-optics present a potential solution to these limitations, existing pure LWIR meta-optics face constraints such as severe chromatic or coma aberrations. Here, we introduce an approach utilizing large-scale hybrid meta-optics to address these challenges and demonstrate the achromatic, coma-corrected, and polarization-insensitive thermal imaging. The hybrid metalens doublet is composed of a metasurface corrector and a refractive lens, featuring a full field-of-view angle surpassing 20° within the 8-12 µm wavelength range. Employing this hybrid metalens doublet, we showcase high-performance thermal imaging capabilities both indoors and outdoors, effectively capturing ambient thermal radiation. The proposed hybrid metalens doublet holds considerable promise for advancing miniaturized, lightweight, and cost-effective LWIR optical imaging systems.

Generation of Perfect Electron Vortex Beam with a Customized Beam Size Independent of Orbital Angular Momentum.

The electron vortex beam (EVB)-carrying quantized orbital angular momentum (OAM) plays an essential role in a series of fundamental research. However, the radius of the transverse intensity profile of a doughnut-shaped EVB strongly depends on the topological charge of the OAM, impeding its wide applications in electron microscopy. Inspired by the perfect vortex in optics, herein, we demonstrate a perfect electron vortex beam (PEVB), which completely unlocks the constraint between the beam size and the beam's OAM. We design nanoscale holograms to generate PEVBs carrying different quanta of OAM but exhibiting almost the same beam size. Furthermore, we show that the beam size of the PEVB can be readily controlled by only modifying the design parameters of the hologram. The generation of PEVB with a customized beam size independent of the OAM can promote various in situ applications of free electrons carrying OAM in electron microscopy.

Dielectric Metasurface for Synchronously Spiral Phase Contrast and Bright-Field Imaging.

Spiral phase contrast imaging and bright-field imaging are two widely used modes in microscopy, providing distinct morphological information about objects. However, conventional microscopes are always unable to operate with these two modes at the same time and need additional optical elements to switch between them. Here, we present a microscopy setup that incorporates a dielectric metasurface capable of achieving spiral phase contrast imaging and bright-field imaging synchronously. The metasurface not only can focus the light for diffraction-limited imaging but also can perform a two-dimensional spatial differentiation operation by imparting an orbital angular momentum to the incident light field. This allows two spatially separated images to be simultaneously obtained, one containing high-frequency edge information and the other showing the entirety of the object. Combined with the advantages of planar architecture and ultrathin thickness of the metasurface, this approach is expected to provide support in the fields of microscopy, biomedicine, and materials science.

Multi-Species Surface Reconstruction for High-Efficiency Perovskite Nanocrystal Light-Emitting Diodes.

Although colloidal perovskite nanocrystal (PNC) solution has exhibited near-unity photoluminescence quantum yield (PLQY), the luminance would be severely quenched when the PNC solution is assembled into thin films due to the agglomeration and fusion of NCs caused by the exfoliation of surface ligands and non-radiative Förster resonance energy transfer (FRET) from small to large particle sizes, which seriously affected the performances of light-emitting diodes (LEDs). Here, we used Guanidine thiocyanate (GASCN) and Sodium thiocyanate (NaSCN) to achieve effective CsPbI3 PNC surface reconstruction. Due to the strong coordination ability of these small molecules with the anions and cations on the surface of the PNCs, they can provide strong surface protection against PNC fusion during centrifugal purification process and repair the surface defects of PNCs, so that the original uniform size distribution of PNCs can be maintained and FRET between close-packed PNC films is effectively suppressed, which allows the emission characteristics of the films to be preserved. As a result, highly oriented, smooth and nearly defect-free high-quality PNC thin films are obtained, with PLQY as high as 95.1 %, far exceeding that of the original film, and corresponding LEDs exhibit a maximum external quantum efficiency of 24.5 %.

Compact meta-optics infrared camera based on a polarization-insensitive metalens with a large field of view.

Metasurfaces have recently emerged as a crucial tool because they achieve spherical-aberration-free focusing when exposed to normal incident light. Nevertheless, these metasurfaces often exhibit considerable coma when subjected to oblique incident light, thereby limiting their imaging field of view. In light of this, our study presents the design and an experimental demonstration of a polarization-insensitive, large-field-of-view metalens that uses a silicon metasurface. The metalens is specifically tailored to the long-wavelength infrared region and possesses a numerical aperture of 0.81, which is capable of focusing light at incident angles up to ±80°. Moreover, we successfully build a meta-optics camera by integrating the large field-of-view metalens on top of an image sensor, thus enabling wide-angle thermal imaging of practical scenes. This research provides new, to the best of our knowledge, insights for designing and realizing large-field-of-view optical systems and holds promise for applications in night vision imaging and security monitoring.

Photonic Spin-Multiplexing Metasurface for Switchable Spiral Phase Contrast Imaging.

As the two most representative operation modes in an optical imaging system, bright-field imaging and phase contrast imaging can extract different morphological information on an object. Developing a miniature and low-cost system capable of switching between these two imaging modes is thus very attractive for a number of applications, such as biomedical imaging. Here, we propose and demonstrate that a Fourier transform setup incorporating an all-dielectric metasurface can perform a two-dimensional spatial differentiation operation and thus achieve isotropic edge detection. In addition, the metasurface can provide two spin-dependent, uncorrelated phase profiles across the entire visible spectrum. Therefore, based on the spin-state of incident light, the system can be used for either diffraction-limited bright-field imaging or isotropic edge-enhanced phase contrast imaging. Combined with the advantages of planar architecture and ultrathin thickness of the metasurface, we envision this approach may open new vistas in the very interdisciplinary field of imaging and microscopy.

Independent Amplitude Control of Arbitrary Orthogonal States of Polarization via Dielectric Metasurfaces.

Exquisite polarization control using optical metasurfaces has attracted considerable attention thanks to their ability to manipulate multichannel independent wavefronts with subwavelength resolution. Here we present a new class of metasurface polarization optics, which enables imposition of two arbitrary and independent amplitude profiles on any pair of orthogonal states of polarization. The implementation method involves a polarization-dependent interference mechanism achieved by constructing a metasurface composed of an array of nanoscale birefringent waveplates. Based on this principle, we experimentally demonstrate chiral grayscale metasurface and chiral shadow rendering of structured light. These results illustrate a general approach interlinking amplitude profiles and orthogonal states of polarization and expands the scope of metasurface polarization shaping optics.

Polarization-independent infrared micro-lens array based on all-silicon metasurfaces.

The long-wavelength infrared (LWIR) micro-lens arrays, as one of the important components in wafer level thermal optics, have been applied for wavefront sensing, beam shaping, integral imaging, and other thermal optical applications. Recently, electromagnetic metasurfaces provide a promising platform for designing high-performance, lightweight and ultracompact optical elements. Here, we experimentally demonstrate a 60 × 60 transmissive type, polarization-independent LWIR micro-lens array based on all-silicon metasurfaces with a fill factor approaching 100%. Each single micro-metalens with a pitch of 100 µm and a focal length of 100 µm operating at λ = 10.6 µm, can focus the light to a spot with a full-width at half-maximum (FWHM) of 12.7 µm (~1.2λ) at the focal plane. Considering the fact of single-step photolithography and standard integrated circuit (IC) compatible fabrication processes, these metasurface-based micro-lens arrays may have great potentials in compact thermal imaging systems.

High-efficiency, linear-polarization-multiplexing metalens for long-wavelength infrared light.

Variable-focus lenses are essential elements of optical systems with extensive applications in microscopy, photography, and optical detection. However, conventional varifocal optical systems obtain a limited tunable capability at the expense of bulk size and slow speed. The metasurfaces are two-dimensional flat structures composed of subwavelength scatterers that exhibit the strong potential for developing ultrathin optics. Here we propose and experimentally demonstrate an all-dielectric polarization-multiplexing metalens with the capability to selectively focus polarized light. The focal length can be controlled by altering the linear polarization state of the incident light. The metalens has focusing efficiencies higher than 72% and exhibits nearly diffraction-limited focusing at long-wavelength infrared frequency. In addition, it is easy to realize high throughput with low manufacturing cost due to the use of complementary metal oxide semiconductor-compatible processes. We envision that this type of polarization-dependent device may pave the way towards the development of compact, multifunctional, and tunable optics.

Efficient EEG Feature Learning Model Combining Random Convolutional Kernel with Wavelet Scattering for Seizure Detection.

Automatic seizure detection has significant value in epilepsy diagnosis and treatment. Although a variety of deep learning models have been proposed to automatically learn electroencephalography (EEG) features for seizure detection, the generalization performance and computational burden of such deep models remain the bottleneck of practical application. In this study, a novel lightweight model based on random convolutional kernel transform (ROCKET) is developed for EEG feature learning for seizure detection. Specifically, random convolutional kernels are embedded into the structure of a wavelet scattering network instead of original wavelet transform convolutions. Then the significant EEG features are selected from the scattering coefficients and convolutional outputs by analysis of variance (ANOVA) and minimum redundancy-maximum relevance (MRMR) methods. This model not only preserves the merits of the fast-training process from ROCKET, but also provides insight into seizure detection by retaining only the helpful channels. The extreme gradient boosting (XGboost) classifier was combined with this EEG feature learning model to build a comprehensive seizure detection system that achieved promising epoch-based results, with over 90% of both sensitivity and specificity on the scalp and intracranial EEG databases. The experimental comparisons showed that the proposed method outperformed other state-of-the-art methods for cross-patient and patient-specific seizure detection.

Broadband and parallel multiple-order optical spatial differentiation enabled by Bessel vortex modulated metalens.

Optical analog image processing technology is expected to provide an effective solution for high-throughput and real-time data processing with low power consumption. In various operations, optical spatial differential operations are essential in edge extraction, data compression, and feature classification. Unfortunately, existing methods can only perform low-order or selectively perform a particular high-order differential operation. Here, we propose and experimentally demonstrate a Bessel vortex modulated metalens composed of a single complex amplitude metasurface, which can perform multiple-order radial differential operations over a wide band by presetting the order of the corresponding Bessel vortex. This architecture further enables angle multiplexing to create multiple information channels that synchronously perform multi-order spatial differential operations, indicating the superiority of the proposed devices in parallel processing. Our approach may find various applications in artificial intelligence, machine vision, autonomous driving, and advanced biomedical imaging.

Excellent thermomagnetic power generation for harvesting waste heat via a second-order ferromagnetic transition.

Thermomagnetic generation (TMG), a promising technology to convert low-grade waste heat to electricity, utilizes high performance TMG materials. However, the drawbacks of large hysteresis, poor mechanical properties and inadequate service life hinder the practical applications. For the first time, we evaluated the effect of different phase transitions on the TMG performance by systematically comparing the TMG performance of three typical Heusler alloys with similar composition but different phase transitions. Ni2Mn1.4In0.6 exhibits second-order magnetic transition (SOMT) from the ferromagnetic (FM) to paramagnetic (PM) state around TC = 316 K without thermal hysteresis. It presents highly comprehensive TMG performance, which is not only better than those of other two Heusler alloys with different phase transitions, but also better than those of most typical TMG materials. The maximum power density (1752.3 mW m-3), cost index (2.78 µW per €), and power generation index PGI (8.91 × 10-4) of Ni2Mn1.4In0.6 are 1-5, 1-4, and 1-7 orders of magnitude higher than those of most typical reported materials, respectively. In addition, Ni2Mn1.4In0.6 with SOMT also shows some advantages that first-order magnetic transition (FOMT) materials do not have, such as zero hysteresis and a long-term service life. In contrast to the short lifetime of a few minutes for the materials with FOMT, Ni2Mn1.4In0.6 with SOMT can serve for one month or even longer with excellent cycling stability. Consequently, we conclude that the SOMT Ni2Mn1.4In0.6 Heusler alloy with good TMG performance as well as zero hysteresis and long service life can be a better candidate than FOMT materials for practical applications of TMG.

Observation of spatiotemporal optical vortices enabled by symmetry-breaking slanted nanograting.

Providing additional degrees of freedom to manipulate light, spatiotemporal optical vortex (STOV) beams carrying transverse orbital angular momentum are of fundamental importance for spatiotemporal control of light-matter interactions. Unfortunately, existing methods to generate STOV are plagued by various limitations such as inefficiency, bulkiness, and complexity. Here, we theoretically propose and experimentally demonstrate a microscale singlet platform composed of a slanted nanograting to generate STOV. Leveraging the intrinsic topological singularity induced by C2 symmetry and z-mirror symmetry breaking of the slanted nanograting, STOV is generated through the Fourier transform of the spiral phase in the momentum-frequency space to the spatiotemporal domain. In experiments, we observe the space-time evolution of STOV carried by femtosecond pulses using a time-resolved interferometry technique and achieve a generation efficiency exceeding 40%. Our work sheds light on a compact and versatile platform for light pulse shaping, and paves the way towards a fully integrated system for spatiotemporal light manipulation.

Themes and ideologies in China's diplomatic discourse - a corpus-assisted discourse analysis in China's official speeches.

Diplomatic discourse is a formalized form of political communication that significantly influences a country's international perception. However, there is a research gap in the analysis of China's diplomatic discourse, particularly in relation to the speeches available on the official Chinese Foreign Ministry website. This study aims to address this gap by conducting a quantitative and qualitative analysis of China's diplomatic speeches. This study utilizes a quantitative corpus-assisted discourse analysis to explore the prevalent themes in China's official speeches. Additionally, qualitative discourse analysis is employed to examine the ideologies manifested in specific examples from the official speeches. The research combines a corpus-based approach with critical discourse analysis to investigate language use, discourse practices, and social practices. The analysis of China's diplomatic discourse reveals several key themes related to President Xi Jinping's leadership, international relations, and future community and economy. The findings provide valuable insights into China's diplomatic strategies and its international image, emphasizing its commitment to cooperation, development, and peace. This research contributes to a better understanding of China's diplomatic discourse and its role in shaping international perceptions of the country. By highlighting the prevalent themes and ideologies in China's official speeches, the study emphasizes China's commitment to fostering positive international relations. The findings offer valuable insights into China's diplomatic strategies and its efforts to shape its international image.

Versatile full-colour nanopainting enabled by a pixelated plasmonic metasurface.

The growing interest to develop modern digital displays and colour printing has driven the advancement of colouration technologies with remarkable speed. In particular, metasurface-based structural colouration shows a remarkable high colour saturation, wide gamut palette, chiaroscuro presentation and polarization tunability. However, previous approaches cannot simultaneously achieve all these features. Here, we design and experimentally demonstrate a surface-relief plasmonic metasurface consisting of shallow nanoapertures that enable the independent manipulation of colour hue, saturation and brightness by individually varying the geometric dimensions and orientation of the nanoapertures. We fabricate microscale artworks using a reusable template-stripping technique that features photorealistic and stereoscopic impressions. In addition, through the meticulous arrangement of differently oriented nanoapertures, kaleidoscopic information states can be decrypted by particular combinations of incident and reflected polarized light.

Untethered Soft Microrobots with Adaptive Logic Gates.

Integrating adaptative logic computation directly into soft microrobots is imperative for the next generation of intelligent soft microrobots as well as for the smart materials to move beyond stimulus-response relationships and toward the intelligent behaviors seen in biological systems. Acquiring adaptivity is coveted for soft microrobots that can adapt to implement different works and respond to different environments either passively or actively through human intervention like biological systems. Here, a novel and simple strategy for constructing untethered soft microrobots based on stimuli-responsive hydrogels that can switch logic gates according to the surrounding stimuli of environment is introduced. Different basic logic gates and combinational logic gates are integrated into a microrobot via a straightforward method. Importantly, two kinds of soft microrobots with adaptive logic gates are designed and fabricated, which can smartly switch logic operation between AND gate and OR gate under different surrounding environmental stimuli. Furthermore, a same magnetic microrobot with adaptive logic gate is used to capture and release the specified objects through the change of the surrounding environmental stimuli based on AND or OR logic gate. This work contributes an innovative strategy to integrate computation into small-scale untethered soft robots with adaptive logic gates.

Vertically Aligned Micropillar Arrays Coated with a Conductive Polymer for Advanced Pseudocapacitance Energy Storage.

With the development of high-performance supercapacitors, a conductive polymer (CP)-based pseudocapacitance electrode with good electrical conductivity and low processing costs holds a promising application prospect. As the core component of supercapacitors, the CP electrode with adjustable spacing, a high specific surface area, and a faster ion diffusion path has been extensively investigated. Herein, based on accurate top-down photolithography and electropolymerization approaches, we fabricate a CP-coated vertically aligned micropillar array (MPA) electrode. The electrode presents an overwhelming enhanced areal specific capacitance compared with that of a flat configuration, which is partially ascribed to an increased electroactive surface area, two rapid channels for ion diffusion and electron transfer, and enhanced electric field intensity that is provided by the MPA structure. Based on the fabricated CP-based MPA electrode, an asymmetric supercapacitor is assembled with two thiophene derivatives, presenting a high energy density and excellent cycling stability. A supercapacitor system cascading with three asymmetric supercapacitor devices further demonstrates the practical applications by driving the light-emitting diodes. This work provides a good reference for the further development of CP-based energy storage devices with high energy density and superior cycling stability.

Broadband generation of perfect Poincaré beams via dielectric spin-multiplexed metasurface.

The term Poincaré beam, which describes the space-variant polarization of a light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM), plays an important role in various optical applications. Since the radius of a Poincaré beam conventionally depends on the topological charge number, it is difficult to generate a stable and high-quality Poincaré beam by two optical vortices with different topological charge numbers, as the Poincaré beam formed in this way collapses upon propagation. Here, based on an all-dielectric metasurface platform, we experimentally demonstrate broadband generation of a generalized perfect Poincaré beam (PPB), whose radius is independent of the topological charge number. By utilizing a phase-only modulation approach, a single-layer spin-multiplexed metasurface is shown to achieve all the states of PPBs on the hybrid-order Poincaré Sphere for visible light. Furthermore, as a proof-of-concept demonstration, a metasurface encoding multidimensional SAM and OAM states in the parallel channels of elliptical and circular PPBs is implemented for optical information encryption. We envision that this work will provide a compact and efficient platform for generation of PPBs for visible light, and may promote their applications in optical communications, information encryption, optical data storage and quantum information sciences.

Multifunctional metasurfaces enabled by simultaneous and independent control of phase and amplitude for orthogonal polarization states.

Monochromatic light can be characterized by its three fundamental properties: amplitude, phase, and polarization. In this work, we propose a versatile, transmission-mode all-dielectric metasurface platform that can independently manipulate the phase and amplitude for two orthogonal states of polarization in the visible frequency range. For proof-of-concept experimental demonstration, various single-layer metasurfaces composed of subwavelength-spaced titanium-dioxide nanopillars are designed, fabricated, and characterized to exhibit the ability of polarization-switchable multidimensional light-field manipulation, including polarization-switchable grayscale nanoprinting, nonuniform cylindrical lensing, and complex-amplitude holography. We envision the metasurface platform demonstrated here to open new possibilities toward creating compact multifunctional optical devices for applications in polarization optics, information encoding, optical data storage, and security.

Low-cost and high sensitivity glucose sandwich detection using a plasmonic nanodisk metasurface.

Glucose detection using surface-enhanced Raman scattering (SERS) spectroscopy has aroused considerable attention due to its potential in the prevention and diagnosis of diabetes as a result of its unique molecular fingerprinting capability, ultrahigh sensitivity and minimal interference from water. Despite numerous solutions to improve the sensitivity of glucose detection, the development of a new SERS-based strategy to detect glucose with high sensitivity and low-cost is still required. In this study, we propose a simple and sensitive SERS-based plasmonic metasurface sensing platform for a glucose sandwich assay using self-assembled p-mercapto-phenylboronic acid (PMBA) monolayers on a gold nanodisk (Au-ND) metasurface and synthesized silver nanoparticles (Ag NPs) modified with a mixture of p-aminothiophenol (PATP) and PMBA. The localized near-field of the proposed plasmonic metasurface is markedly enhanced due to the coupling between the Au-ND and Ag NPs, which greatly improves detection sensitivity. The experimental results show that SERS signals of the glucose assay are significantly enhanced by more than 8-fold, in comparison with the SERS substrate of smooth Au films and Ag NPs. Moreover, the plasmonic metasurface-based glucose sandwich assay exhibits high selectivity and sensitivity for glucose over fructose and galactose. The developed plasmonic metasurface sensing platform shows enormous potential for highly sensitive and selective SERS-based glucose detection and opens a new avenue for scalable and cost-effective biosensing applications in the future.