Boron carbide (B4C) is widely used as a coating material for x-ray optics in X-ray Free Electron Laser (XFEL) beamlines. In this study, single-shot damage experiments were conducted on B4C/Si-sub and B4C/Cr/Si-sub mirrors at 517 eV using the Shanghai Soft x-ray free electron laser. The damage thresholds were determined to be 0.49 ± 0.13 and 0.32 ± 0.08 J/cm2 for B4C/Si-sub and B4C/Cr/Si-sub, respectively. Morphological and microstructural characterizations reveal that XFEL-induced damage in both samples is closely related to thermal melting of the Si substrate. Based on the silicon melting criterion, the theoretical damage threshold simulated by the finite element method for B4C/Si-sub is in good agreement with the experimental result. The bump damage morphology observed at a fluence of 0.66 J/cm2 for this sample is attributed to the volumetric expansion of the molten Si substrate. In contrast, the silicon melting criterion overestimates the damage threshold for the B4C mirror with a Cr adhesive layer. The lower experimental threshold of B4C/Cr/Si-sub is attributed to the interfacial diffusion reaction and the femtosecond XFEL-induced cavitation, which leads to a more readily observable damage morphology.

The inhomogeneity of spin angular momentum (SAM) of light generates optical forces by the transverse Belinfante spin momentum (BSM). This BSM-induced force, though has theoretically been predicted to reverse sign with the size and refractive index of the Mie particle, lacks experimental validation. Here, using a typical line-shaped beam that mitigates the influence of light gradient and spin-orbit interaction, we observe distinct inverse optical forces on Mie particles when their sizes are varied. In addition, BSM-induced forces on polystyrene and silica particles can exhibit either the same or opposite signs at certain particle sizes. The good agreement of experimental results with simulations in this work uncovers a generic reversible force effect on Mie particles, the exhibition of which can be expected in various types of optical forces, including optical gradient force, radiation pressure, pulling force, etc. This work enriches the physics of optical forces and has broad applications in optical sorting and microscale motors.

Hyperspectral imaging technology has become an important tool in modern optical detection due to its advantage of integrating spectra. When using hyperspectral data for quantitative analysis, radiometric calibration is essential for converting raw digital signals into reflectance. However, standard diffuse panels are inevitably contaminated in practical applications, leading to a decrease in radiometric calibration accuracy and introducing systematic errors. Traditional methods such as manual cleaning are not only expensive to maintain, but also difficult to implement rapidly in unattended automated hyperspectral systems. In this study, we propose a contamination-aware empirical line method (CA-ELM) based on a wide-band hyperspectral imaging system (400-1700 nm), which aims to reduce the effect of localized contamination on the standard diffuse panels in radiometric calibration. By combining spectral feature clustering and spatial edge detection methods, CA-ELM adaptively identifies and excludes contaminated areas of the diffuse panels. Only the field-measured reflectance of the clean areas is reserved for radiometric calibration. In the case of localized contamination of the diffuse panels, the average reflectance error of CA-ELM compared to the empirical line method decreased from 4.58 % to 3.08 %, which approached the performance of calibration based on clean diffuse panels. Further validation using the random forest algorithm for hyperspectral classification of seven samples showed that the model achieved an average classification accuracy of 98.86 % for CA-ELM calibrated images, which was 4.60 % higher than the empirical line method. In the experimental scenario where it is difficult to clean or replace diffuse panels in time, CA-ELM provides an effective solution to the problem that the calibration accuracy decreases due to localized contamination of the panels. This study verifies the feasibility of CA-ELM under laboratory conditions, and provides technical support for the realization of automated and robust hyperspectral radiometric calibration.

Predicting the degradation of heterogeneous nanolayers under energetic particle irradiation remains challenging due to complex coupling across atomic-to-macroscopic scales. Using W/Si multilayers as a representative system, we investigate structural degradation under 22 and 40 keV proton irradiation. Transmission electron microscopy demonstrates depth-dependent period compaction and asymmetric interface broadening, while energy-dispersive spectroscopy and X-ray photoelectron spectroscopy reveal damage mechanisms of enhanced atomic interdiffusion and WSi2 formation under proton irradiation. Monte Carlo simulations uncover that this asymmetry stems from a longer backward mean diffusion length of Si atoms compared to forward ones. A cross-scale framework bridging atomic-scale mechanism, nanostructural evolution and macroscopic optical property is established. The agreement between simulated and experimental X-ray reflectivity confirms the degradation mechanism and the validity of the framework. This study deepens the understanding of proton radiation damage in X-ray mirrors and provides a new paradigm for evaluating structure evolution and simulating performance degradation of nanoscale multilayers in extreme environments.

Chip-scale nonlinear optics enables strong light-matter interactions within compact devices, serving as a fundamental platform for multifunctional integrated photonics from classical optical signal processing to quantum information technologies. Transition metal dichalcogenide (TMDC) waveguides have recently emerged as a highly promising platform owing to their giant material nonlinearity and extended interaction lengths. To date, however, research has predominantly focused on conversion efficiency, leaving the mechanisms governing the polarization state of nonlinear signal largely unexplored. Here, we establish a comprehensive framework for engineering the polarization of second-harmonic generation (SHG) in 3R-MoS_2 waveguides. By synergizing polarization-resolved measurements with theoretical modeling, we reveal that the SHG polarization is determined by guided-mode interactions constrained by waveguide geometry and crystal symmetry, and further reshaped during propagation. We demonstrate that thickness-dependent guided-mode confinement and in-plane crystal symmetry provide robust, static control over SHG polarization, while propagation length offers a dynamic tuning knob for continuously tailoring the nonlinear output. Our findings provide a deterministic approach for on-chip polarization engineering, opening opportunities for reconfigurable nonlinear light sources and quantum photonic circuits.

The polished surface quality of coatings has been the key aspects that directly determine the optical performance of telescope, especially for the high-resolution ones, e.g., space telescope, while giant electrorheological polishing is one of the most promising techniques to achieve superior surface finish of components. A multiscale methodology, integrating molecular dynamics simulations with first-principles calculations, is adopted in this investigation to reveal the material removal mechanisms of different micro-polishing parameters. In surface–microscale, molecular dynamics simulations were employed to model material removal behavior during polishing, where abrasive particles slide across the workpiece surface, and the influence patterns of multiple polishing parameters were systematically investigated. It was found that the indicators of stress, strain, and atomic stacking exhibit a core characteristic of “depth-dominated, velocity-regulated” response to processing parameters. At subsurface–mesoscale, the characterization of subsurface structures under different parameters revealed patterns in lattice evolution, dislocation dynamics, and surface defect characteristics during polishing. As polishing depth increases, the internal dislocation density of the material progressively rises, during which a distinctive three-dimensional tetrahedral stair-rod dislocation ring structure emerges. At atomic–electronic scale, a combination of first-principles calculations and molecular dynamics simulations was employed to further evaluate the mechanical properties of Ni-coatings. First-principles calculations and electron density analysis together elucidate the anisotropic elasticity of Ni-coatings, revealing the orientation-dependence of the elastic modulus and confirming the 111 plane as the shear weak plane. This study provides mechanistic support for optimizing Ni-coating polishing parameters and enhancing the surface quality of optical components.

The imaginary Poynting momentum (IPM), as an intrinsic yet mysterious property of light, is nearly as ubiquitous as its real counterpart. However, prior research has only traced its origin to intensity asymmetry and showcased its capability in particle manipulation using evanescent waves and structured light. Fundamentally, the interplay between the IPM and polarization topology remains unexplored, significantly restricting its potential applications. Here, we observe the high-order polarization topological charges (PTCs) in the IPM and expand their capabilities in versatile particle manipulation. PTCs originate from spatial distributions of linear polarizations in vector beams. When the PTC equals 1, the IPM can be utilized to rotate particles. Distinctively, for higher-order PTCs, rotational potential-well arrays with controllable rotation directions emerge to trap and rotate various numbers of particles. This work uncovers a holistic and complete understanding of the IPM by investigating its link to the polarization distribution. It also suggests a credible way to harness polarization-topology optical forces, offering significant potential for biophysical and quantum applications.

Quantum technologies have surpassed classical systems by leveraging the unique properties of superposition and entanglement in photons and matter. Recent advancements in integrated quantum photonics, especially in silicon-based and lithium niobate platforms, are pushing the technology toward greater scalability and functionality. Silicon circuits have progressed from centimeter-scale, dual-photon systems to millimeter-scale, high-density devices that integrate thousands of components, enabling sophisticated programmable manipulation of multi-photon states. Meanwhile, lithium niobate, thanks to its wide optical transmission window, outstanding nonlinear and electro-optic coefficients, and chemical stability, has emerged as an optimal substrate for fully integrated photonic quantum chips. Devices made from this material exhibit high efficiency in in generating, manipulating, converting, storing, and detecting photon states, thereby establishing a basis for deterministic multi-photon generation and single-photon quantum interactions, as well as comprehensive frequency-state control. This review explores the development of integrated photonic quantum technologies based on both silicon and lithium niobate, highlighting invaluable insights gained from silicon-based systems that can assist the scaling of lithium niobate technologies. It examines the functional integration mechanisms of lithium niobate in electro-optic tuning and nonlinear energy conversion, showcasing its transformative impact throughout the photonic quantum computing process. Looking ahead, we speculate on the developmental pathways for lithium niobate platforms and their potential to revolutionize areas such as quantum communication, complex system simulation, quantum sampling, and optical quantum computing paradigms.

The evolution of silicon surface roughness is studied under scanning ion beam etching for high precision manufacture applications. The experiment is carried out using an 800 eV Ar ion beam generated through metal mask and different etching depths from 240 nm to 1330 nm was carried out. The processed surface is characterized via atomic force microscope, grazing incidence X-ray reflectivity, and X-ray fluorescence spectroscopy, to study the surface morphology, optical contrast and composition changes. It is found that the processed surface is smoothed from 0.14 nm to 0.10 nm (Root mean square) in the initial stage of etching, while further etching (deeper than similar to 1 mu m) would cause growth of nanodots structure with increased roughness. Contaminants sputtered from the ion beam mask and sample holder are detected on the processed surface and the related agglomeration and micro-masking effects of the contaminants are considered as the main mechanism for surface roughening. The roughened surface can be smoothed from 0.41 nm down to 0.10 nm (Root mean square) using the same etching parameters with only similar to 10 nm etching depth after exposure to air. The results show that the surface smoothing or roughening mechanism of Si can be closely related to the surface composition and structure, which provide useful guidance for the manufacture of high precision and ultrasmooth optics.

Bonnet and wheel polishing techniques have been widely adopted to fabricate ultrasmooth surfaces for extreme ultraviolet and X-ray optical systems. However, conventional methods inevitably generate undesirable anisotropic textures aligned along the polishing direction. Discrete precession polishing offers a promising solution for eliminating these textures; however, the accurate prediction of surface roughness evolution during this process remains a significant challenge. This paper presents a mathematical model and numerical simulation framework for surface texture evolution in discrete precession polishing using root-mean-square (RMS) roughness as the surface quality indicator. Unlike the conventional assumption of a monotonic decrease in the surface roughness, our model reveals a three-stage evolution pattern: initial reduction, subsequent increase, and eventual convergence to a fixed RMS roughness value. The parametric analysis indicates that reducing the polishing tool profile roughness and increasing the number of precession angles can effectively improve the final surface quality. Experimental validation confirmed the accuracy and reliability of the model. Through model-guided optimization, we successfully achieved a surface with 0.41 nm RMS roughness over a measurement area of 640 μm × 480 μm, demonstrating the practical applicability of this model for high-precision optical surface fabrication.

The internal layer structure and optical performance of B4C coating for X-ray free-electron laser (XFEL) applications were studied. Surface morphology analysis shows that the B4C layer growth at 5 mTorr replicates the substrate morphology at low and mid frequencies but adds slight high-frequency roughness, with the RMS value increasing from 0.13 to 0.33 nm. To investigate the internal physical and chemical structure of B4C, angle-resolved X-ray photoelectron spectroscopy (ARXPS) and depth profiling were performed. Together with soft X-ray (SXR) and hard X-ray (HXR) reflectivity measurements and the fitted results, a three-sublayer model with different composition and density was built for the 50 nm B4C coating. The developed B4C coating was further deposited on a 600 mm length mirror with a thickness variation of 0.7 nm (peak-to-valley). The radius of curvature changed slightly from 181 km before coating to 128 km after coating, and the slope errors were maintained at around 0.07 µrad, indicating a high-performance and large-size B4C coating for the XFEL.

Rhombohedrally stacked transition metal dichalcogenides such as 3R-MoS_2 offer an exceptional platform for nonlinear optics, naturally forming Fabry-Pérot (FP) microcavities due to their giant dielectric contrast with the surrounding media. However, rigorously tracking the evolution of multiple harmonic fields within these unpatterned monolithic crystals remains a fundamental challenge. Here, we establish a self-consistent framework, spanning from linear broadband reflectance to second- and third-harmonic generation (SHG and THG), to systematically decode these nonlinear behaviors. Moving beyond conventional models, we demonstrate that the nonlinear emission is dictated by a delicate interplay among the intrinsic material absorption, the FP effects at the fundamental frequency, as well as those at the harmonic frequencies. When harmonic photons lie below the bandgap, weak absorption allows the nonlinear spectra to exhibit a complex modulation driven by the synergistic contribution of FP effects from both fundamental and harmonic waves. In stark contrast, severe intrinsic absorption of higher-energy photons heavily damps the FP effects of the harmonic fields, reducing the nonlinear response to an absorption-limited regime modulated almost exclusively by the FP effects at the fundamental frequency. By successfully decoupling these geometric and material contributions across different harmonic orders, our findings provide a precise design paradigm for engineering next-generation van der Waals photonic architectures.

The growing demand for compact, lightweight, and cost-effective long-wave infrared (LWIR) optical systems has driven interest in metalenses. However, their performance is limited by the aperture-dispersion trade-off. Existing dispersion compensation strategies are limited by the constrained phase modulation ranges and dispersions of these unit cells, making it difficult to simultaneously achieve large apertures, broad operational bandwidths, and high numerical apertures. To address this, we propose a spectrum-informed computational deblurring framework for correcting chromatic aberrations in LWIR metalens imaging. The first stage employs a Wiener filtering network for preliminary correction, followed by a U-Net architecture for refined image restoration. We demonstrate this approach using a 2-cm aperture, 0.45-NA (numerical aperture) ultrathin metalens (0.4-mm thickness, 0.38-g mass) fabricated via standard deep silicon etching techniques. Experimental validation reveals significant improvements in image quality compared to the unprocessed image: the peak signal-to-noise ratio (PSNR) increases from 13.73 to 21.90 dB, and the structural similarity index measure (SSIM) improves from 0.496 to 0.836. These results effectively overcome limitations of conventional dispersion compensation methods, resolving the aperture-dispersion tradeoff. The proposed ultrathin imaging system offers a transformative pathway for next-generation portable LWIR devices, with strong potential in applications such as security surveillance, industrial inspection, and mobile thermal sensing.