The sophisticated shaping of electromagnetic field landscapes, both outside and inside optical cavities, has long been an important goal of optics and photonics, with broad applications in near-field imaging, lithography, and laser science. Despite extensive progress in far-field shaping of extracavity landscapes, achieving accurate tailoring of three-dimensional intracavity fields has remained elusive. Here, we propose full-space adjoint-enabled freeform meta-optics for complex, on-demand vector field shaping of intracavity landscapes. In contrast with conventional semi-space adjoint approaches, the full-space adjoint strategy allows for efficient full-wave optimization of vector fields at the subwavelength scale, overcoming strong multiple scattering and interference intrinsic to enclosed cavity boundaries. We experimentally demonstrate tailored plasmonic cavity landscapes with a freeform metasurface mask, realizing a fivefold enhancement in imaging fidelity without sacrificing optical super-resolution performance. Our work significantly broadens the scope of freeform meta-optics and may open new avenues for applications in nanophotonics, topological photonics, and quantum optics.

In this paper, we propose a new strategy based on the interconversion between two symmetry-protected bound states in the continuum(SP-BICs) to break the high symmetry dependency of the SP-BIC. The excitation of four high-Q quasi-BIC resonances is supported by disrupting both the translational and structural symmetry of the metasurface using spacing and length perturbations, respectively. Furthermore, interconversion between the two SP-BICs can be achieved via length perturbation, significantly diminishing the radiative attenuation rate of the quasi-BIC. Despite a relative asymmetric parameter reaching 97.2%, the Q-factor order of magnitude of the quasi-BIC can remain constant. Compared with previous studies,our approach significantly enhances the robustness of the Q-factor for the quasi-BIC by a minimum of two orders of magnitude, although our relative asymmetric parameter is approximately 10 times the corresponding work.

Light beam carrying spin angular momentum (SAM) and orbital angular momentum (OAM) have attracted great interest due to their great potential for high‐capacity optical communication, optical tweezers, and quantum information. However, the current detection methods suffer from the lack of robustness to misalignments in the optical system, which limits the detection accuracy and the application for off‐axis vortex array detection. Here, a high‐efficiency, broadband, and single‐layer metasurface design is proposed for alignment‐free angular momentum detection via spin‐independent astigmatic transformation (SIAT). The SAM and OAM states can be recognized from the diffraction direction and patterns, respectively. Proof‐of‐concept demonstrations are experimentally carried out on different incident beams including circular‐polarization, linear‐polarization, and vector vortex beams, as well as vortex beam arrays, showing a high diffraction efficiency of ≈81% at 1064 nm while operating within the broadband region of 900–1300 nm. The alignment‐free merit for the incident position, incident angle, and detector distance grants the device great potential for integrated quantum systems and multiparticle micromanipulation with optical tweezers.

Asymmetric spin–orbit interaction (ASOI) breaks the limitations in conjugate symmetry of traditional geometric phase metasurfaces, bringing new opportunities for various applications such as spin-decoupled holography, imaging, and complex light field manipulation. Since anisotropy is a requirement for spin–orbit interactions, existing ASOI mainly relies on meta-atom with C1 and C2 symmetries, which usually suffer from an efficiency decrease caused by the propagation phase control through the structural size. Here, we demonstrate for the first time that ASOI can be realized in meta-atoms with rotational symmetry ≥3 by combining the generalized geometric phase with the propagation phase. Utilizing an all-metallic configuration, the average diffraction efficiency of the spin-decoupled beam deflector based on C3 meta-atoms reaches ∼84 % in the wavelength range of 9.3–10.6 μm, which is much higher than that of the commonly used C2 meta-atoms with the same period and height. This is because the anisotropy of the C3 metasurface originates from the lattice coupling effect, which is relatively insensitive to the propagation phase control through the meta-atom size. A spin-decoupled beam deflector and hologram meta-device were experimentally demonstrated and performed well over a broadband wavelength range. This work opens a new route for ASOI, which is significant for realizing high-efficiency and broadband spin-decoupled meta-devices.

The spread of the SARS-CoV-2 virus has had an unprecedented impact, both by posing a serious risk to human health and by amplifying the burden on the global economy. The rapid identification of the SARS-CoV-2 virus has been crucial to preventing and controlling the spread of SARS-CoV-2 infections. In this study, we propose a multilayered plasmonic nanotrap (MPNT) device for the rapid identification of single particles of SARS-CoV-2 virus in ultra-high sensitivity by surface-enhanced Raman scattering (SERS). The MPNT device is composed of arrays of concentric cylindrical cavities with Ag/SiO2/Ag multilayers deposited on the top and at the bottom. By varying the diameter of the cylinders and the thickness of the multilayers, the resonant optical absorption and local electric field were optimized. The SERS enhancement factors of the proposed device are of the order of 108, which enable the rapid identification of SARS-CoV-2 N protein in concentrations as low as 1.25 × 10-15－12.5 × 10-15 g mL-1 within 1 min. The developed MPNT SERS device provides a label-free and rapid detection platform for SARS-CoV-2 virus. The general nature of the device makes it equally suitable to detect other infectious viruses.

The adverse impact of atmospheric aerosols on both the environment and human health has become a major concern in recent years. The detailed characterization of atmospheric aerosols is crucial to understanding their formation and their sources of origin, which then allows to take effective measures to control air pollution. However, the precise characterization of atmospheric aerosols is still a challenge, mainly due to the low concentration of the constituents that make up the chemical composition of aerosols. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical technique for the identification and characterization of biological and chemical species. SERS combines the advantage of single-molecule sensitivity with being a non-destructive technique and is therefore promising for the analysis of atmospheric aerosols. In recent years, our group, as well as other research groups, have been actively developing SERS technique for the characterization of atmospheric aerosols. Here, we present a comprehensive review of the recent progress in SERS and its application in the characterization of atmospheric aerosols. We first discuss the principle of SERS, after which we give an overview of the preparation of SERS substrates and the characterization of atmospheric aerosol with SERS. Finally, we present the challenges and future perspectives in this area.

Moiré fringe has become one of the mainstream methods for high-precision distance measurement at present, and the accuracy of moiré fringe-based distance measurement can reach the nanometer level. However, due to the discrete sampling of moiré fringe images by camera and the non-integer sampling, spectral leakage occurs during Fourier transform, thereby affecting the measurement accuracy. By applying a 2D-windowing process to the moiré fringe, the spectral leakage can be effectively reduced and the accuracy of the moiré fringe phase demodulation improved. This paper conducted a simulation analysis on moiré fringes formed by three sets of gratings with different periods and obtained the most suitable window function for each of them. Finally, one set of the gratings was selected for height displacement measurement experiments on a wafer stage. The experimental results achieved a measurement accuracy better than 5nm.

Characterization of atmospheric fine particulate matter (PM2.5) in large cities has important implications for the study of their sources and formation mechanisms, as well as in developing effective measures to control air pollution. Herein, we report a holistic physical and chemical characterization of PM2.5 by combining surface-enhanced Raman scattering (SERS) with scanning electron microscopy (SEM) and electron-induced X-ray spectroscopy (EDX). PM2.5 particles were collected in a suburban area of Chengdu, a large city in China with a population over 21 million. A special SERS chip composed of inverted hollow Au cone (IHAC) arrays was designed and fabricated to allow direct loading of PM2.5 particles. SERS and EDX were used to reveal the chemical composition, and particle morphologies were analyzed from SEM images. SERS data of atmospheric PM2.5 indicated qualitatively the presence of carbonaceous particulate matter, sulfate, nitrate, metal oxides and bioparticles. The EDX showed the presence of the elements C, N, O, Fe, Na, Mg, Al, Si, S, K, and Ca in the collected PM2.5. Morphology analysis showed that the particulates were mainly in the form of flocculent clusters, spherical, regular crystal shaped or irregularly shaped particles. Our chemical and physical analyses also revealed that the main sources of PM2.5 are automobile exhaust, secondary pollution caused by photochemical reactions in the air, dust, emission from nearby industrial exhaust, biological particles, other aggregated particles, and hygroscopic particles. SERS and SEM data collected during three different seasons showed that carbon-containing particles are the principal sources of PM2.5. Our study demonstrates that the SERS based technique, when combined with standard physicochemical characterization methods, is a powerful analytical tool to determine the sources of ambient PM2.5 pollution. Results obtained in this work may be valuable to the prevention and control of PM2.5 pollution in air.

Plasmonic imaging lithography is a novel way for nanofabrication, with the advantages of low-cost, high yield, and large area, having potentially promising applications in a variety of nanostructures manufacturing. However, previous reports on plasmonic imaging lithography mainly focus on the simulation and experimental research of fixed period or fixed structure size metasurface fabrication, which limits the range of its application. In this paper, we proposed and analyzed the imaging lithography characteristics of the reflective plasmonic structure, selected the best structure in the fabrication process by parameter analysis, and reached a conclusion that the air gap has the greatest influence on imaging quality of reflective plasmonic imaging lithography. Then we experimentally demonstrated its ability in fabricating multi-scale patterns. A 10mm×16mm large-scale printing metasurface with periods from 414.3 nm to 580 nm has been proposed and manufactured. Furthermore, the feasibility of exposing functional metasurface whose radius varies from 75 nm to 150 nm is also verified under the same condition. The proposed method has widespread applications in multifunctional metasurface devices.

Particle contamination of photo masks is a significant issue facing the micro-nanofabrication process. It is necessary to analyze the particulate matter so that the contamination can be effectively controlled and eliminated. In this study, Raman spectroscopy was used in combination with scanning electron microscopy with energy analysis (SEM-EDX) techniques to study the contamination of individual particles on the photomask. From Raman spectroscopic analysis, the Raman bands of particles mainly contributed to the vibrational modes of the elements C, H, O, and N. Their morphology and elemental composition were determined by SEM-EDX. The sizes of the particles are mostly less than 0.8 μm according to the SEM image analysis. Hierarchical clustering analysis (HCA) of the Raman spectra of particles have shown that the particles can be classified into six clusters which are assigned to CaCO3, hydrocarbon and hydrocarbon polymers, mixture of NH4NO3 and few (NH4)2SO4, mixtures metal oxides, D and G peaks of carbon, fluorescent and (NH4)2SO4 clusters. Finally, principal component analysis (PCA) was used to verify the correctness of the classification results. The identification and classification analysis of individual particles of photomask contamination illustrate the chemical components of the particles and provide insights into mask cleaning and how to effectively avoid particle contamination.

Multispectral imaging plays an essential role in applications from biomedical imaging to remote sensing since it records rich spectral and spatial information. Nevertheless, conventional multispectral imaging systems generally suffer from complicated optical systems and compromise between spectral, spatial, and temporal resolution. Multispectral scattering imaging has recently drawn considerable attention due to its simple setup and unique methodology to solve the aforementioned bottlenecks. Herein, multispectral scattering imaging based on metasurface diffuser and deep learning is proposed. Prior knowledge of the metasurface diffuser's wavefront will avoid the time‐consuming characterization required in conventional scattering media, and a well‐trained deep learning algorithm can realize real‐time image reconstruction. With these merits, this method may push the development of metasurface applications and multispectral imaging.

Arrays of gold–silver (Au–Ag) bimetallic nanopillars were fabricated by a newly developed surface-plasmon lithography (SPL) and their enhancement properties as surface-enhanced Raman scattering (SERS) substrates have been studied. We demonstrated that the SPL is a low-cost and high efficiency method for the fabrication of SERS substrates with both high sensitivity and reproducibility. The nanopillars showed a good response in the detection of methylene blue molecules at a low concentration of 1.0 × 10–11 mol· l−1. The SERS enhancement factors (EFs) are on the orders of 107 and the relative standard deviation of SERS intensity is <8% over an area of 50 μm × 50 μm. The EFs increase fast with the height increasing from 200 to 530 nm, then increase slowly when further increase the height of the nanopillars to 1100 nm. In addition, the Au–Ag bimetallic coating has shown much higher SERS enhancement than the coatings of either the pure Au or Ag. The excellent SERS enhancement and reproducibility of the Au–Ag coated nanopillars indicated that the fabricated SERS substrates can be used for the detection of biochemical molecules at trace level and the SPL is a promising method for fabrication of SERS substrates.

Lithography is one of the most key technologies for integrated circuit (IC) manufacturing and micro/nano-functional device fabrication, while the imaging objective lens plays one important role. Due to the curved surface of the conventional objective lens, the imaging field of view is limited and the objective lens system is complex. In this paper, a planar objective lens based on the optical negative refraction principle is demonstrated for achieving optical axis free and long depth of focus imaging nanolithography. Through employing a hyperbolic metamaterial composed of silver/titanium dioxide multilayers, plasmonic waveguide modes could be generated in multilayers, which results in optical negative refraction and then flat imaging at ultraviolet wavelength. The corresponding imaging characteristics are investigated in simulation and experiment. At the I-line wavelength of 365 nm, the highest imaging resolution of 165 nm could be realized in the 100 nm photoresist layer under the working gap of 100 nm between the objective lens and substrate. Moreover, this planar objective lens has good ability for cross-scale and two-dimensional imaging lithography, and is similar to a conventional projection objective lens. It is believed that this kind of planar objective lens will provide a promising avenue for low-cost nanofabrication scenarios in the near future.

Plasmonic imaging technology can offer a novel way for nanofabrication, with the advantages of low-cost, high yield, and large area, having potentially promising applications in various nanostructures manufacturing. However, the previous studies mainly focus on the simulation and experimental research of fixed period or fixed structure size metasurface fabrication, which limits the range of its applications. In this paper, we proposed and analyzed the imaging characteristics of the reflective plasmonic structures, selected the best structure in the fabrication process by parameter analyses, and concluded that the air gap has the most significant influence on imaging quality of plasmonic imaging technology. Then we experimentally demonstrated its ability in fabricating multi-scale patterns. A 10mm × 16 mm large-scale structural color metasurface with periods from 414.3 to 580 nm has been designed and manufactured. Furthermore, the feasibility of fabricating metasurface whose radius varies from 75 to 150 nm is also verified under the same condition. The proposed method is expected to have widespread applications in multi-functional metasurface devices.

As an intrinsic nature of light, polarization plays a critical role in the vectorial characteristic of optical fields. Vector optical fields with an inhomogeneous polarization distribution show many exotic phenomena and applications not existing in scalar optical fields. Existing polarization optics, however, mainly focuses on the manipulation of polarization distribution on a single transverse plane. Here, we propose a synthetic approach to realize polarization manipulation with spatial and temporal degrees.The underlying mechanism relies on decoupling two orthogonal polarization states through asymmetric photonic spin-orbit interactions to obtain customer-tailored phase and amplitude difference in both transverse and longitudinal space, thereby changing the resulting polarization distribution at will in three-dimensional(3 D) space. Remarkably, a longitudinally varied cylindrical vector field is experimentally demonstrated by a monolayer metasurface, in which the polarization distribution switches continuously and periodically between radial and azimuthal polarization. Furthermore, the vector field can be dynamically tuned by rotating the incident polarization state. Our work extends polarization optics from two-dimensional space to 3 D space, allowing the arbitrary generation and manipulation of 3D vector optical fields with temporal tunability.

Ultra-high-speed laser cladding technology is used to clad the surface anti-corrosion layer of tungsten cathode for molten salt electrolysis. Using MSC. Marc finite element simulation software, optical microscope (OM), scanning electron microscope (SEM), energy spectrum (EDS), X-ray diffractometer (XRD) and microhardness tester and other analytical testing methods, respectively, the cladding process, the cladding layer microstructure morphology, phase composition, phase distribution and microhardness are simulated, and the structure is observed and analyzed. The simulation results show that the preheating process before cladding for the tungsten substrate can effectively avoid the cracking phenomenon caused by internal stress; the structure and performance observation results show that the cladding layer has a dense structure and no cracks, forming a good metallurgical bond with the substrate, the difference in the structure of the cladding layer affects the hardness of the cladding layer.

We design a simple catenary metasurface with high efficiency, which could obtain both the degree of circular polarization and the wavelength of incident polarized light by measuring the diffraction intensity and the deflection angle. The catenary decomposes the incidence into left and right circularly polarized light and diffracts them to different predesigned directions with different deflection angles that present the wavelength information. The diffraction efficiency of the designed catenary exceeds 94%, the average diffraction efficiency is up to 97.6% at the wavelength of 8-14μm, and angular dispersion is 0.078°/nm. Moreover, the degree of circular polarization for various incident polarization states can be characterized by diffraction intensities. This work may provide extensive applications for biosensing, DNA structural analysis, stereochemistry, etc.

Multispectral imaging technology plays an important role in lots of domains, but traditional systems are limited by large volumes and complex constructions. Here, we propose a high-efficiency multispectral integrated imaging system based on metasurfaces, with its spectral range covering two important infrared windows of 3-5 μm and 8-12 μm. This system is composed of the microlens, metasurface, and filter array, hence its volume, weight, and complexity can be greatly decreased. The average efficiencies of the aforementioned two bands are over 96.47% and 97.43%, respectively. The bandwidth of each spectral channel can be tuned flexibly according to realistic requirements, which makes the system more applicable to various circumstances. The proposed design method is universally applicable and has potential applications in many aspects, such as remote sensing, epidemic monitoring, and archeology.

We designed a broadband achromatic multilevel diffractive lens which is using the nanoparticle composite. Nanoparticle composite is a new artificial material, which has both pattern-transfer capability and high refractive index requirements. The device has good achromatic performance and good focusing performance at the focal plane in the visible band. The simulated average focusing efficiency is over 85% at the visible frequency.

We report a lightweight metasurface with wide field of view (FOV), which can calculate incident angle by the focus of the sun for navigation. The solar altitude angle and solar azimuth angle for navigation can be resolved with converting the coordinate system to connect the sun with the focus. The designed metasurface overcomes bulky devices and bad weather owing to the fact that the metasurface operates at short-wavelength infrared band (SWIR) that penetrates smoke and fog.