Zhengxiang Shen

The elliptical cylindrical mirror has been utilized in neutron small-angle scattering and reflectometry to enhance the neutron intensity at the sample position. However, the performance of the elliptical cylindrical mirror can be impacted by surface slope errors, reflectivity, and misalignments. In this work, the performance of the elliptical cylindrical mirror under different error conditions has been analyzed comprehensively, and a 250-mm-long elliptical cylindrical mirror was designed and developed. The simulations show that a source size below 1 mm is required to achieve a peak gain above 6, with a theoretical peak gain of 16× with a 0.1 mm source. The rotational misalignment of 0.03° around the Y-axis can decrease gain from 16× to 6×. The designed mirror was fabricated with a surface figure error of 110 nm (RMS), and a roughness below 0.5 nm (RMS), and was coated with an m = 4 supermirror. The mirror was aligned and tested in the dedicated neutron beamline of the Chinese mianyang research reactor, and the results show a peak gain of 12.77 with a 0.1 mm slit source.

Turbid underwater images often suffer from color distortion, contrast degradation, and detail loss. To improve the visual quality of these images, this paper proposes an illumination-constrained, structure-preserved retinex variational model. The proposed approach consists of three main components: a nonlinear model based on the classical retinex theory to represent the multiple adverse deformations of turbid underwater images; an adaptive channel compensation method to correct the color cast; and an illumination-constrained structure-preserved variational retinex model that simultaneously estimates a smooth illumination component and a detail display reflection component and uniformly predicts the noise pattern of preprocessed underwater images. Specifically, an adaptive weight matrix is proposed to reveal the structural details in reflectance. The overall smoothness of illumination is constrain by exponential guided filtering and l1/2 norm. The total intensity of the noise pattern is constrained by l2 norm. To solve the resulting optimization problem, we employ alternating direction minimization of logless transformations of Lagrange multipliers. Extensive experiments demonstrate the effectiveness of the proposed method in improving the quality of turbid underwater images. Beyond subjective visual observations, the method also exhibits competitive performance in objective image quality evaluations.

Integral field spectroscopy (IFS) is capable of simultaneously collecting two-dimensional high-resolution spatial image information and spectral information in a target field of view (FOV). The image slicer is the key element in IFS for segmenting the target FOV. Current micro-image slicer fabrication methods such as molecular assembling need strictly accurate control during sticking, which is time-consuming and expensive. In this study, we improved a direct-adhesive method for thin glass slicer manufacture and alignment. Thin glass is fabricated via single polishing and direct stitching to form a micro-image slicer. Based on charge coupled device (CCD) camera tests on parallel light, the manufacture accuracy for a six-channel image slicer reaches that of the molecular assembling scheme. This method can be applied to the fabrication of image slicers with different apertures.

Imagery captured in extreme underwater environments often presents unique challenges, including blurred details, color distortion, and reduced contrast. These discrepancies largely emanate from the intricate interplay of light absorption and scattering within the aquatic medium. Predominant restoration techniques, rather simplistically, apply a static attenuation coefficient, neglecting the dynamic nuances of underwater conditions, leading to an inconsistent restoration outcome. To counter these impediments, we introduce an avant-garde Underwater Internet of Things (Underwater IoT) system, underpinned by a scene-depth fusion paradigm. Our methodology astutely accounts for the spectral decay of light underwater to infer a more refined attenuation coefficient tailored to the specific scene. This system, employing a quadtree decomposition for precise localization coupled with depth mapping, facilitates an astute estimation of prevailing luminescence. This depth map, once synthesized and refined, aids in gauging the precise attenuation dynamics of the aqueous milieu, culminating in a more precise transmission map derivation. Segueing from this, we employ an inverse model to refurbish the original image. Experimental results highlight our system’s prowess in counteracting issues like muddied details and chromatic anomalies while concurrently amplifying contrast. In juxtaposition with a spectrum of existing methodologies, our innovation outshines in terms of finesse and accuracy, underscoring its unparalleled efficacy in the challenging underwater conditions.

Contact method is an important method to measure the complex permittivity of polymer films. There are some possible factors affecting its accurate measurement for thin films by direct contact method. To solve the problem, this paper analyzes the reasons of errors induced by flatness tolerance and edge effect from the view of three-electrode structure, and that induced by the state of film surface as well. An equivalent electric circuit model is proposed based on direct contact method and the state of film surfaces. The correction formulas used to measure complex permittivity of films with coarse surface are derived according to the model, and then verified by experimenting different materials. Experimental results show that errors of relative permittivity are under 5% after calculation by the correction formula. In conclusion, the proposed measurement technique is theoretically and practically applicable for the complex permittivity measurement of low-thickness polymer films about 10~100 μm.

The diamond-turning process is a mean optical surface generation technique with high figure accuracy and surface finish. The diamond-turned surface has a significant diffraction effect introduced by the tool marks remaining on the surface, which heavily degrade the optical performance in the visible wavelength spectrum. The traditional approach that was used to eliminate this effect was polishing. In this paper, we present a method to find turning parameters that can generate an optical surface without diffraction effect directly by coupling a surface micro-topography model of a turned surface via the scattering theory. The surface micro-topography model of the turned surface reveals the relationship between tool marks and the diamond-turning parameters (DTPs). The scattering theory reveals the relationship between diffraction intensity distributions (DIDs) and surface micro-topography of the turned surface. Therefore, we obtained the relationship between DIDs and DTPs. The diffraction effect is considered to be eliminated when the first-order diffraction intensity is less than 0.01% of incidence intensity. The criterion of turning parameters for diffraction elimination is then obtained. Finally, turning experiments are performed to confirm the effectiveness of this method, and the diffraction-free surface finish is achieved.

For higher detection capability, dual band/dual field of view (FOV) infrared imaging systems are often used to recognize camouflaged targets. In this Letter, we report a dual band/dual FOV infrared imaging system with freeform prism, in which the optical path is folded drastically. Each spectral band will pass through the same entrance pupil and then is split off by a beam splitter so that each spectral band can match a different FOV. Compared to traditional infrared imaging systems, the proposed system has advantages of less volume, higher integration, and optical efficiency.

Differential deposition and profile coating are two common deterministic fabrication methods for figure correction of high-precision mirrors. The generation of the desired particle distribution on the substrate as the growing function is an important prerequisite, especially for two-dimensional correction. A model of particle distribution considering the etched ring shape, mask structure, and mask distance between the target and substrate is established. The model is verified by deposition experiments using a series of circular holes with different hole sizes and distances of the mask from the substrate. According to the model, a smallest deposition beam width of 2.79 mm can be obtained using a hole with a 3 mm diameter. The shape of the particle distribution gradually changes from convex to concave as the mask moves away from the substrate for different holes. A two-dimensional figure correction of a flat mirror was demonstrated using a hole with a 6 mm diameter. The peak-to-valley (PV) value is reduced from 74.23 nm to 10.09 nm, and the root mean square (RMS) value is reduced from 18.38 nm to 1.36 nm within a 130 mm × 20 mm area. The model could provide useful guidance for high-precision two-dimensional figure correction applications.

Ultra-precision diamond machining is a promising technique for non-rotationally symmetrical surfaces with sub-micrometer form accuracy. The measurement and compensation processes in the fabrication process must be conducted carefully to achieve high form accuracy. However, significant challenges remain to improve the measurement accuracy and machining efficiency. Because of the remounting process, the off-machine measurements would reduce the efficiency. On the other hand, contact-type measurements can cause physical damage to some soft materials. To overcome these problems, a noncontact on-machine measurement (OMM) system is developed using two optical probes, and a two-step compensation strategy is proposed to generate a modified tool path. To verify the accuracy of the proposed measurement system, OMMs were performed on a spherical mirror using this system and were later compared with off-machine measurements. To evaluate the compensation strategy, an off-axis paraboloid mirror was diamond-machined and compensated using the proposed method. The results show that the OMM system and compensation strategy are effective for improving the form accuracy while simultaneously enhancing the machining efficiency.

The nested grazing incidence telescope can achieve a large collecting area in x-ray astronomy, with a large number of closely packed, thin conical mirrors. Exploiting the surface metrological data, the ray tracing method used to reconstruct the shell surface topography and evaluate the imaging performance is a powerful tool to assist iterative improvement in the fabrication process. However, current two-dimensional (2D) ray tracing codes, especially when utilized with densely sampled surface shape data, may not provide sufficient accuracy of reconstruction and are computationally cumbersome. In particular, 2D ray tracing currently employed considers coplanar rays and thus simulates only these rays along the meridional plane. This captures axial figure errors but leaves other important errors, such as roundness errors, unaccounted for. We introduce a semianalytic, three-dimensional (3D) ray tracing approach for x-ray optics that overcomes these shortcomings. And the present method is both computationally fast and accurate. We first introduce the principles and the computational details of this 3D ray tracing method. Then the computer simulations of this approach compared to 2D ray tracing are demonstrated, using an ideal conic Wolter-I telescope for benchmarking. Finally, the present 3D ray tracing is used to evaluate the performance of a prototype x-ray telescope fabricated for the enhanced x-ray timing and polarization mission.