Wheel-type elastic emission machining (EEM) holds great promise for achieving atomic-level, low-damage optical fabrication. However, existing material removal models fail to account for the inherently coupled physicochemical removal mechanism of EEM, leaving deterministic process control a challenge. In this study, a physicochemical synergistic material removal model was developed for wheel-type elastic emission machining, and an optimal process window was established. A three-dimensional fluid-structure interaction (FSI) simulation model was constructed to resolve the fluid pressure, wall shear stress, and velocity distributions at the polishing interface, while simultaneously capturing the elastic deformation of the polyurethane polishing wheel. The results confirm that the predicted removal profiles are in excellent agreement with the experimental measurements, with coefficients of determination exceeding 0.99 in both the XZ- and YZ-planes. Experimental investigations revealed a three-stage nonlinear response of removal depth to polishing speed, polishing time, and polishing gap. Normalized sensitivity analysis indicated that polishing time is the dominant factor, followed by the polishing gap and polishing speed. A hierarchical optimization framework was adopted, in which efficiency served as a hard constraint and stability was maximized among all qualified candidates. The resulting optimal process window achieves a synergistic balance between high removal efficiency and disturbance rejection. This work provides reliable process guidance for the application of wheel-type EEM to atomic-level fabrication of ultra-precision optical surfaces.

Reaction-bonded silicon carbide (RB-SiC) is the preferred material for space optical systems because of its low density and high specific stiffness. However, its hardness and multi-component properties lead to low efficiency and pit defects during the polishing process, making the fabrication of RB-SiC a significant challenge. This study proposes a high-efficiency and low-defect fabrication method for RB-SiC using center-inlet computer-controlled polishing (CCP). We first investigated the polishing efficiency and surface quality achieved with center-inlet and non-center-inlet liquids. The results show that the defect density under non-center-inlet conditions was positively correlated with process parameters, while fewer defects and higher efficiency could be achieved under center-inlet conditions. Additionally, the efficient removal and defect suppression mechanisms under the center-inlet condition were revealed based on machining force, heat, and defect characterization. Under center-inlet conditions, the friction coefficient is larger and stable, resulting in high removal efficiency. The macro-micro coupled analysis results show that pit defects are generated through the combined action of force and heat, which leads to the thermo-mechanical degradation and shedding of SiC particles due to the temperature increase in the machining zone. The results demonstrate that center-inlet CCP not only ensures sufficient abrasion at the polishing interface to achieve high removal efficiency but also significantly suppresses the processing heat, thereby resulting in a low-defect surface.

Grain boundary (GB) misorientation in magnesium (Mg) alloys is known to influence plastic deformation; however, its role in governing yield strength remains unclear. Here, we elucidate the microstructural origin of misorientation-dependent yielding in an AZ31 Mg alloy by integrating quasi-in-situ SEM-EBSD, high-resolution digital image correlation (HR-DIC), and crystal plasticity finite element modeling (CPFEM). Two samples with nearly identical grain sizes and Schmid factor (SF) distributions but distinct GB misorientations were examined under compression along the extrusion direction (EDC) and rolling direction (RDC). Despite comparable {10−12} extension twinning activity, the EDC exhibits ∼28% higher yield strength than the RDC. The observed strength difference is associated with distinct intergranular compatibility, enhanced activation of non-Schmid basal slip, and greater grain-scale stress heterogeneity. In the EDC, larger GB misorientation restricts intergranular strain transfer associated with twinning, leading to pronounced strain incompatibility. To maintain deformation continuity, non-Schmid basal slip is activated alongside elastic strain accumulation, resulting in persistent grain-scale stress concentration. Displacement gradient tensor analysis reveals that this non-Schmid basal slip serves primarily as a local geometrical accommodation process—compensating for transverse strain mismatch between neighboring grains with incompatible twin variants—rather than as a direct load-carrying mechanism. In contrast, efficient intergranular compatibility in the RDC promotes homogeneous deformation and suppresses stress heterogeneity, leading to lower yield strength. These findings establish an experimentally supported association among GB misorientation characteristics, intergranular compatibility, stress heterogeneity, and macroscopic yielding, suggesting a compatibility-controlled strengthening mechanism and providing a mechanistic basis for strengthening Mg alloys through GB engineering beyond conventional grain size and texture optimization.

The advancement of high temperature resistant thin film strain sensors is crucial for detecting surface strain changes in aerospace turbine engines and launch vehicles. However, the strain sensitivity under high temperature thin film strain gauges is generally low, resulting in minimal resistance change under unit strain. In this regard, we proposed a thin film (thickness:similar to 500 nm) strain sensor, consisting of a composite structure including indium tin oxide with unconventional ratio (5-5 ITO, In2O3:SnO2 = 50:50 wt%) and Pt. Surprisingly, the strain sensor demonstrates ultrahigh sensitivity (gauge factor (GF) > 120, maximal GF = 178), rapid response time (0.12 s), as well as long cycling durability (10 h) under an operating temperature of 500 degrees C. The outstanding dynamic strain response and long-term temperature cycling stability of sensor originate from the micro-cracks in the sensitive film. The 5-5 ITO thin film produces island-like gaps with stress concentration in high-temperature environments, leading to a significant increase in resistance. Meanwhile, the top layer Pt structure covers the 5-5 ITO film, which aids in better recovery of micro-cracks, enhancing sensor repeatability and cycle durability. With its rapid response time, high sensitivity, and consistent performance at high temperatures, our strategy for this sensor holds great promise for applications in monitoring under extreme environment conditions.

Significance Large-aperture potassium dihydrogen phosphate (KDP) and deuterated potassium dihydrogen phosphate (DKDP) crystals are the only nonlinear optical materials suitable for serving as frequency conversion elements and optical switches in high-power laser facility. However, their anisotropy, soft-brittleness, hygroscopicity, thermal sensitivity, and propensity for cracking impose significant challenges to ultra-precision manufacturing. Conventional grinding and polishing processes are prone to leaving abrasive particles embedded on the surface. These particles serve as precursors to laser-induced damage, significantly diminishing the laser damage resistance of the crystals. Consequently, the simultaneous attainment of full spatial-frequency bandwidth precision and a high laser-induced damage threshold (LIDT) constitutes a pivotal challenge in the advancement of high-power laser facility. Progress To address these challenges, an integrated technical route of "single-point diamond turning (SPDT) + sub-nanosecond laser conditioning + sol-gel coating" has been established. Significant progress has been made in the following areas. Ultra-precision cutting technology and equipment: an anisotropic constitutive model for soft-brittle crystals was developed to reveal the brittle-ductile transition (BDT) behavior during cutting (Fig. 1). Simulations identified the optimal cutting direction along 45 degrees within the (001) plane and a BDT depth of approximately 150 nm. Through process optimization and the innovative design of an integrated vacuum chuck with variable hole density and active temperature control (Fig. 2), surface figure accuracy better than 4 lambda (lambda=632.8 nm) and sub-nanometer roughness [root mean square (RMS)=0.59 nm] were achieved on large-aperture KDP crystals. Surface defects induced by fly-cutting, such as brittle indentations, cracks, protrusion pressure points, ballast, and plastic scratches, were systematically characterized (Fig. 4). Fluorescence microscopy (405 nm) revealed that defects like brittle indentations, cracks, protrusions, and ballast exhibit higher fluorescence intensity than defect-free regions, indicating stronger laser energy absorption and lower LIDT (Fig. 5, Table 1). An explosion simulation model was innovatively proposed to quantify the damage thresholds for different defect types and to elucidate the underlying damage mechanisms (Fig. 8). This model simplifies the complex multi-field coupling problem into a quantifiable explosive process, revealing that local mechanical strength and absorption capability are key factors affecting LIDT. Sub-nanosecond laser conditioning: the mechanisms underlying laser conditioning for the elimination or passivation of both point defects and structural defects were elucidated. A pulse width of 500 ps was identified as the optimal parameter within the 300?800 ps range, as it provides sufficient peak power for electronic excitation while exceeding the lattice heat transfer time necessary for thermal effects. After applying this offline conditioning process to 400 mm aperture DKDP crystals, under ultraviolet laser irradiation, the surface damage density was reduced from 5.02 to 0.55 pp/cm(2), and the bulk damage density decreased from 2?3 to 0.3?0.8 pp/mm(3) (Fig. 10, Table 2), marking a critical step toward engineering application. Sol-gel coatings: to enhance environmental stability and optical performance, multifunctional coatings were developed via sol-gel methods. Moisture barrier coating a novel network-ball embedded structure was created by embedding hexamethyldisilane (HDMS)-modified SiO2 nanoparticles into a siloxane polymer matrix (Fig. 11). This structure yields a tunable refractive index (1.21?1.44), high hydrophobicity (contact angle increased to 109.4 degrees), and exceptional moisture resistance (less than 0.1% transmission loss after 27 weeks at 80% relatively humidity). Antireflective (AR) coating: using methyltriethoxysilane (MTES) to seal surface pores after HMDS modification, an AR coating with low residual reflectance (less than 0.5%@355 nm), high LIDT (more than 20 J/cm(2)), and excellent oil contamination resistance (only 0.097% transmission drop after 20 weeks) was achieved (Fig. 12). Bilayer coating system a precisely designed bilayer system for dual-wavelength (527 nm & 351 nm) antireflection was realized. It combines a high-refractive-index moisture barrier layer and a low-refractive-index AR layer, exhibiting outstanding optical uniformity and environmental stability (0.7% transmission drop after 19 weeks in high humidity) (Fig. 13). Conclusions and Prospects This review comprehensively summarizes recent breakthroughs in ultra-precision manufacturing technology for large-aperture KDP/DKDP crystals achieved through an integrated process route. Significant advances in fly-cutting theory and equipment, defect characterization and suppression, laser conditioning, and functional coating design have collectively and notably enhanced the surface accuracy, laser damage resistance, and environmental stability of these critical optical components. Looking forward, future research should prioritize several key directions: 1) exploring novel processes such as ultra-precision polishing to further suppress mid-spatial-frequency ripples induced during machining; 2) developing multifunctional composite coatings that exhibit lower curing temperatures, higher LIDT, and extended operational lifetimes; and 3) establishing a full-process database that correlates manufacturing defects with damage performance, along with developing efficient, non-destructive online evaluation techniques for comprehensive performance assessment of large-aperture crystal components.

KDP crystals are essential for high-energy laser systems due to their unique optical properties, yet their brittleness and stress sensitivity present challenges for ultra-precision machining. Single-point diamond fly-cutting (SPDF) is preferred for high-accuracy machining of large KDP components, but tool wear remains a critical issue due to transient impact forces generated with each tool-crystal contact. While most research has focused on steady-state conditions, the effects of transient impacts on tool wear and surface quality are often overlooked. This study addresses this gap by developing and validating a novel tool wear model that includes dynamic interactions between the diamond tool and KDP crystals. Models for cutting forces and stress distributions under both steady-state and transient conditions were established, followed by a tool cutting edge wear model that incorporates these effects. Results show that maximum transient stresses reach 3.28 GPa at the separation point between the rake face and cutting edge, while stresses on the cutting edge itself reach 1.46 GPa. These elevated stress levels lead to tool wear rates in SPDF that are 2.46 times higher than those under steady-state conditions in turning. Additionally, progressive tool wear and an adhesive layer in SPDF increase surface roughness, producing deeper, irregular scratches beyond typical feed marks. The adhesive layer forms through chemical adsorption onto oxygen-containing groups on the worn tool surface, with hydrogen bonding within the chips. These insights support optimizing machining parameters to enhance tool longevity and surface quality in KDP crystal applications.

Potassium dihydrogen phosphate (KDP) crystals, vital for high-power laser systems, pose significant machining challenges due to their brittleness, low hardness, and hygroscopic properties. Achieving crack-free, high-precision surfaces is essential but complex. Single-point diamond fly-cutting (SPDF) is the primary method, yet it exposes tools to high mechanical stress and heat, accelerating wear. In dry cutting, worn tools develop adhesive layers that detach, causing scratches and degrading surface quality. Traditional wet cutting improves surface finish but leaves residual fluids that contaminate the surface with metal ions, leading to optical degradation and fogging. To address these issues, this study explores mixed-fat-based minimum quantity lubrication (MQL) as a sustainable alternative, comparing two lubricants: biodegradable-base mixed ester lubrication (BBMEL) and hydrocarbon-based synthetic lubricant (HCBSL). A comprehensive evaluation method was developed to analyze surface roughness, tool wear, and subsurface damage under dry cutting, MQL-BBMEL, and MQL-HCBSL conditions. Experimental results show that MQL-BBMEL significantly enhances machining performance, reducing average surface roughness by 27.77% (Sa) and 44.77% (Sq) and decreasing tool wear by 25.16% compared to dry cutting, outperforming MQL-HCBSL. This improvement is attributed to BBMEL’s lower viscosity and higher proportion of polar functional groups, which form stable lubricating films, minimizing friction and thermal effects. Structural analyses confirm that MQL-BBMEL prevents KDP crystal deliquescence and surface fogging. These findings establish MQL-BBMEL as an eco-friendly, high-performance solution for machining brittle optical materials, offering significant advancements in precision machining for high-power laser systems.

WMoTaNb RHEA has been manufactured using vacuum levitation melting. The as-cast WMoTaNb RHEA has equiaxed grains with a mean grain size of 71.4 mu m, and the analysis of the experimental results of thermal conductivity, thermal expansion, and TG-DSC suggests that the as-cast WMoTaNb RHEA has excellent stability at elevated temperature above 1400 degrees C. This result experimentally explains the previous research on phase and microstructure stability. This study can provide experimental evidence for the high-level stability and help explain the elevated temperature mechanical behaviors of the as-cast WMoTaNb RHEA at elevated temperatures.

At present, a single post-processing technology will always introduce secondary defects (trace pollution elements and structural defects) while removing surface processing defects of fused silica components, which limits the further improvement of the laser damage threshold of the components. Therefore, to effectively remove surface defects in optically-processed fused silica and suppress defect regeneration is the key to improve the laser damage resistance performance of the components. Based on the complementarity of anisotropic ion beam etching and isotropic HF acid etching, a combined etching technology is proposed for fused silica components used in engineering. The combined etching can remove most of the fragmented defects on fused silica surface to achieve relatively good surface quality with a root mean square roughness of 0.666 nm. After the combined etching, the contents of most impurity elements decrease by approximately an order of magnitude. Besides, the contents of the structural defects significantly reduce. Therefore, The zero probability damage threshold and the 100 % probability damage threshold increase by 32.41 % and 57.46 %, respectively. The results show that the combined etching technology can effectively improve the laser damage resistance performance of fused silica components, especially under high fluence laser irradiation, which is very important for the high power output and stable operation of laser facilities.

Using Python language to import Voronoi diagrams into ABAQUS, a two-dimensional microscopic model of vibration cutting of 45 steel is established, and based on this model, the stress changes of grains and grain boundary units on the cutting path are analyzed. The results show that in ultrasonic vibration cutting, the direction of normal stress and shear stress in the grain fracture unit will reverse, and the energy threshold will be reached during multiple impact processes, resulting in failure and deletion; During the impact process, grain boundaries are more prone to advanced failure under normal stress.

Accurate determination of optical properties is crucial for optimal application of HfO2 film in optoelectronic industry. In this work, the effects of additional oscillator(s) introduced into Tauc-Lorentz model (the improved TL model) on the extracted optical properties of HfO2 film have been investigated with a roughness layer considered or not. The results show that the effect of additional oscillator(s) on optical properties depends on the electronic structure of HfO2 film, i.e., amorphous and/or polycrystalline character. The appearance of a shoulder -like absorption peak at similar to 6 eV and a weak discrete absorption peak at similar to 5.2 eV on the curve of dielectric function of the 350 nm polycrystalline HfO2 film confirms that additional oscillators correspond well with changes of the electronic structure probably induced by crystal field and defects. The results indicate that the improved TL model can be well applied to crystalline/polycrystalline films as well as defects near the absorption edge, and further probably to the fine electronic structure of materials, which greatly extends the application of TL model.

In view of the problem that various fused silica materials have different characteristics, which could cause differences in processability, the mechanical properties of fused silica materials were studied through nanoindentation experiments. Relationship curves between indentation load and material hardness/elastic modulus were obtained for different fused silica optics. The fracture characteristics of fused silica materials were also studied using the gradient force imprinting method, and the fracture toughness and critical load of crack generation were calculated for different fused silica materials. The ability of different fused silica materials to resist crack instability prop agation under the same process conditions was also clarified. Furthermore, the polishing removal characteristics of fused silica materials were researched, and the polishing removal efficiency of different materials was obtained through the magnetorheologi cal finishing (MRF) spotting method. It was further verified that the hardness was positively correlated with the material polishing removal efficiency. Based on the characteristics of different fused silica materials, the optical ultra -precision processing parameters could be selected. This is of great significance for low -defect and high-efficiency ultra-precision machining of optics.

The traditional polishing method inevitably results in subsurface cracks in the fused silica, which seriously degrades their ultraviolet laser damage resistance. CO2 laser irradiation can melt these cracks and improve their laser induced damage threshold (LIDT). Photoluminescence spectrum and SEM-FIB were employed to investigate the changes in the material microstructure at the crack location with CO2 laser melting. The density of the oxygen-deficient centers of type II (ODC II) defects decreases, while the density of the non-bridging oxygen hole center (NBOHC) defects increases after high-temperature melting. The reason for this change is related to the dihydroxylation reaction and the participation of environmental oxygen in the defect type conversion. The reduction of ODC II defects is most likely the reason for the improvement of LIDT.

In the field of numerical control machining, tool alignment technology is a key link to ensure machining accuracy and quality. Tool alignment refers to determining the correct position of the tool relative to the workpiece, and its accuracy directly affects the precision of part machining. With the development of precision machining technology, the research and application of cutting technology are increasingly valued. Tool alignment methods are mainly divided into two categories: contact and non-contact. The contact type tool alignment method relies on direct contact between the tool and the workpiece or tool alignment instrument to measure the position. Among them, the trial cutting method is a traditional contact type tool alignment method that determines the tool position through actual cutting, which is intuitive but inefficient. The contact type tool presetter uses specialized equipment to improve the accuracy and efficiency of tool presetting through contact measurement. The non-contact tool alignment method does not rely on physical contact, while the image method uses image recognition technology to determine the tool position, making it suitable for high-precision applications. The laser diffraction method and the laser direct method use laser technology for non-contact measurement. The laser diffraction method determines the position of the tool by analyzing the diffraction mode of the laser beam, while the laser direct method directly measures the distance between the laser and the tool. This article mainly introduces the classification of tool alignment, commonly used knife alignment methods and common tool alignment devices, as well as the development status of international tool alignment instrument products.

Aluminum (Al)-based metal-dielectric composite coatings play a crucial role in the production of vacuum ultraviolet (VUV) optical components and laser systems. In the short-wavelength range of the VUV region, there is a high demand for practical Al-based coatings with high reflectivity, which imposes strict requirements on the preparation process. Key parameters of the preparation process, such as deposition rate, film thickness, and deposition temperature, significantly influence the growth and short-wavelength VUV optical properties of the coatings. In this study, we utilized electron-beam evaporation technology to prepare magnesium fluoride (MgF2) protected Al coatings for short-wavelength VUV reflection. We explored the impact of the aforementioned key process factors on the coatings’ properties and improved the reflectivity of the coatings in the short-wavelength VUV range, achieving reflectivity above 85% at the wavelength of 121.6 nm.

Aiming at the problem of on-line real-time monitoring of grinding wheel wear state in ultra-precision grinding, the wear experimental research of fused silica optics is carried out by using acoustic emission technology. The grinding wheel wear state is determined according to the micro morphology of grinding wheel surface. On this basis, the variation law of acoustic emission signal with grinding wheel wear state is revealed, and the quantitative relationship between the root mean square value of acoustic emission signal, grinding force grinding, wheel spindle power and grinding wheel wear state is built. The wavelet packet transform is used to decompose the acoustic emission signal, studying the variation law of root mean square value of acoustic emission signal in different frequency bands under different grinding wheel wear, taking it as the feature of grinding wheel wear, and obtaining the early warning threshold for grinding wheel wear passivation according to the micro morphology of grinding wheel surface. It’s helpful to monitor and control the wear state of diamond grinding wheel in the grinding process of optics through the analysis of acoustic emission signal, so as to improve the grinding efficiency and quality of optics.

A large-aperture silicon carbide (SiC) aspheric mirror has the advantages of being light weight and having a high specific stiffness, which is the key component of a space optical system. However, SiC has the characteristics of high hardness and multi-component, which makes it difficult to realize efficient, high-precision, and low-defect processing. To solve this problem, a novel process chain combining ultra-precision shaping based on parallel grinding, rapid polishing with central fluid supply, and magnetorheological finishing (MRF) is proposed in this paper. The key technologies include the passivation and life prediction of the wheel in SiC ultra-precision grinding (UPG), the generation and suppression mechanism of pit defects on the SiC surface, deterministic and ultra-smooth polishing by MRF, and compensation interference detection of the high-order aspheric surface by a computer-generated hologram (CGH). The verification experiment was conducted on a Ø460 mm SiC aspheric mirror, whose initial surface shape error was 4.15 μm in peak-to-valley (PV) and a root-mean-square roughness (Rq) of 44.56 nm. After conducting the proposed process chain, a surface error of RMS 7.42 nm and a Rq of 0.33 nm were successfully obtained. Moreover, the whole processing cycle is only about 216 h, which sheds light on the mass production of large-aperture silicon carbide aspheric mirrors.