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Microlens arrays (MLAs) made from fused silica possess broad applications in wavefront sensing, optical focusing, beam shaping, etc. However, it is challenging to fabricate the hard-brittle silica MLAs with high accuracy and low cost by conventional manufacturing techniques efficiently. In this work, a novel two-step method, which consists of rapid evaporative ablation and precision melting polishing by CO2 lasers, is proposed to fabricate high-quality MLAs. The first step is to rapidly ablate and engrave micro-pillar arrays (MPAs) with flat groove bottom by high-energy density CO2 lasers. The second step is to precisely polish and shape the flat-topped MPAs into the dome-topped MLAs with good surface roughness (Sa) by low-energy density CO2 lasers. The whole preparation process could be achieved through a set of machining system. Firstly, the geometric dimension (period, p and height, h) of the microlens is determined by the Monte Carlo ray tracing method. Secondly, to diminish the groove depth inconsistency caused by heat accumulation, the multiple ablation compensation strategy is developed. The MPAs (p = 200–400 μm), of which maximum height error is 7.1%, are prepared in 1 s by the proposed compensation strategy. Then, the MPAs are smoothed into the MLAs by low-energy density CO2 lasers, and the average Sa is improved from 960 nm to 32.56 nm. Finally, the optical performances of the MLAs are verified from the effectiveness of imaging, focusing and homogenization. The proposed two-step processing method paves a new way to fabricate high-performance MLAs on hard-brittle fused silica with low cost and high efficiency.

This paper aims to conduct tool wear experiments on cutting SiCp/Al composite materials, and methodically reveal the wear evolution of PCD tools in some detail. Based on the experiments, five-tool wear schemes are rationally developed, including free from wear, crater wear, flank wear, combined crater and flank wear, and edge blunting. The accurate equivalent homogeneous material (EHM) turning simulation model of SiCp/Al composite material is constructed and verified using AdvantEdge software. Subsequently, comprehensive studies have been conducted to analyze the effect of various tool wear patterns on the SiCp/Al cutting process. The results indicate that the crater wear of the tool is positively correlated with the radius of curvature of the chip. Additionally, the flank wear of the tool demonstrates a negative correlation with both the thickness and length of the chips. The actual cutting temperature is 11.3% lower compared to the simulated data, whereas the actual cutting forces in the X and Y directions are 16.1% and 13.7% higher, respectively. The flank wear degree of the tool and the edge blunting both remarkably influence the cutting force in the Y direction and the surface residual stress after machining. As the degree of wear increases, the cutting force in the Y direction and the surface residual stress rise, and the penetration layer of the residual stress becomes deeper, which is attributed to the significantly enhanced ploughing effect of the tool. This study provides a valuable reference for predicting the wear status of cutting tools, particularly in machining difficult-to-machine materials.

Graded polycrystalline copper materials have been expected in the field of scientific research and engineering in recent years because the core of the material has enough toughness and a sufficient surface strength. However, the plastic deformation mechanism, gradient grain generation mechanism and material strengthening principle of polycrystalline copper are still not well understood. Therefore, it is urgent to further analyze the plastic deformation of polycrystalline copper. In this study, the micron scale plastic deformation behavior of polycrystalline copper is simulated based on the crystal plasticity finite element method. The simulation analysis is carried out from the aspects of grain size, grain shape, crystal orientation type and quantity, loading mode and so on. The effects of the above parameters on the Mises stress nephogram and stress-strain curve of polycrystalline copper were analyzed. At the end of the article, the EBSD orientation distribution information of graded polycrystalline copper grains obtained in the cutting process is analyzed comprehensively and the formation mechanism of graded polycrystalline copper is explained by combining the simulation results.

Multi cycle injection and production of underground gas storage (UGS) promote continuous changes in reservoir characteristics, to clarify the impact of different injection and production characteristics on the reservoir, taking carbonate rock fracture-pore type gas storage reservoirs as the research object, established a set of experimental methods based on production characteristics, quantitative analysis of reservoir damage caused by particle migration caused by increasing, decreasing, fluctuating, and reverse changes in production pressure difference. And the following research results are obtained. First, established experimental methods based on production characteristics, the production method includes increasing, decreasing, fluctuating, and reverse changes, realized experimental evaluation of simulating actual production full features. Second, there is a critical pressure difference in the migration of reservoir particles, the fluctuation of production pressure difference induce further migration of particles, resulting in natural unblocking or new blockage. Third, the change in the direction of production pressure difference can cause large particle sizes break into small particle sizes and migrate out of the pore throat, thus the permeability of the reservoir can be improved to a certain extent. It is concluded that controlling a certain production pressure difference during the injection and production process of UGS, not only meets production needs, but also alleviate the damage of injection production to reservoir permeability to a certain extent.

The intrinsic heat-affected zone (HAZ) during the microsecond pulsed laser processing significantly affect the surface quality of the fused silica optics. This study employed both three-dimensional numerical simulations and experiments to analyze the heat accumulation effect, morphology evolution mechanism, and the HAZ distribution during CO2 laser processing of fused silica. Simulation results show that with the increases of process parameters such as the laser frequency, the overlap rate, and the pulse width, the residual temperature of the substrate rises gradually. The excessive laser repetition frequency mainly causes the heat accumulation and over-ablation. Analysis of the laser processed surface demonstrates that the superposition of the laser spot energy results in the periodic texture whose spatial internal is equal to the feeding distance of the laser spot. Increasing the track pitch will make the ridges and grooves of the ripple structure discrete, while reducing the laser moving speed within a certain range can improve the surface quality. Besides, the fictive temperature of the substrate tends to stabilize after the third laser pulse in each track. The thickness of the HAZ is close to the material removal depth, but it can be effectively suppressed with a pulse width less than 10 μs. Experiments are conducted to validate the simulation and the results match well with each. This study can provide a theoretical guidance for producing high-quality fused silica optics in high-power laser device applications.

Background: Residential surrounding greenness may be protective of dyslipidemia are often theorized but remain poorly quantified. In particular, the underlying biological mechanisms of blood lipid changes with green spaces remain unclear. Methods: Our observational epidemiology study included a residentially stable sample of 1035 coronary heart disease patients, and proteomics study included 16 participants. Normalized Difference Vegetation Index (NDVI) was used to evaluate residential greenness exposures. Proteomics technology was used to identify plasma greenness-related proteome disturbance, and the pathway analysis was employed to evaluate the potential biological mechanisms of greenness decreasing dyslipidemia risk. Result: Higher residential surrounding greenness in the 500-m area was associated with lower risks of dyslipidemia (odds ratio (OR) = 0.871, 95% confidence interval (CI): 0.763, 0.994 for per one-quartile NDVI increase). Lymphocytes mediated 18.7% of the association between greenness and dyslipidemia. Greenness related proteins (including PLXDC1, IGFBP2 and LY6D) may regulate the biological functions of lipid metabolism and transport-related proteins (including ADIPOQ and CES1) through a series of biological processes. Conclusion: People in greener surroundings have a lower risk of dyslipidemia, which may be due to their lower inflammation, stronger lipid transporter activity, and normal cholesterol metabolism.

As a rapid and efficient processing technology, CO2 laser processing has been applied to remove fused silica materials. However, thermal effect caused by CO2 laser would lead to thermal modification layer, thermal deformation and residual stress in processed fused silica optics. To reduce the thermal effect, high power and short pulse CO2 laser is applied to remove the surface material of fused silica. In this work, a model coupling the physical processes of heat transfer and phase transition was established to simulate the complex interaction of CO2 laser with fused silica. Then, the model was applied to investigate the evolutions of temperature distribution and surface morphology involved in the laser ablating and melting processes. The results indicate that with the increase of laser power and decrease of pulse width, positive effect would take place that the radius-depth ratio of ablating area increases and the heat-affected area becomes smaller. For the application of CO2 laser with 0.2 μs pulse width and 800 kW peak power, fused silica material would quickly reach the ablation state. The ablation depth is less than 1 μm, and the thickness of heat-affected area is about 80 nm. It means that the high power and short pulse CO2 laser is equivalent to a hot grinding ball head, which can remove the material rapidly with small heat-affected area on fused silica surface. The simulation results of line scanning processing with CO2 laser were finally compared with the experiment ones, which verified the feasibility of the established model. The suggestions and prospective for improving the model were put forward as well. Keywords: CO2 laser, Fused silica, Heat-affected area, Laser processing

Micromachining repair of surface defects on KH2PO4 (KDP) optics is an emerging technique in the construction of Inertial Confinement Fusion facilities for obtaining clean nuclear fusion energy. However, this method is yet facing considerable challenges owing to the soft-brittle nature of single-crystal KDP, hence it is necessary to understand its ductile-regime cutting mechanism to generate crack-free surfaces. This paper seeks to investigate the evolution of different cutting mechanism with the change of uncut chip thickness (UCT) in KDP orthogonal cutting processes. A transition of cutting modes from plastic cutting to shear-crack cutting and then fracture cutting with the rise of UCT has been revealed. To explain these cutting phenomena, a novel theoretical model was proposed by calculating the specific energy dissipation for crack/fracture propagations during cutting processes based on fracture mechanics. This analytical model was well validated by the analysis of cutting forces and machined surface quality. Nevertheless, three kinds of surface defects have been observed, i.e. micro pits, micro craters and edge chipping. These surface defects were caused by tearing and spalling of materials with elastic recovery, crack propagation along cleavage planes with ploughing effect, and the peeling away of large-size fracture, respectively. The presented results of great significance for promoting the application of micromachining processes in future engineering repair of KDP optics.

Localized CO2 laser repairing of surface damage on fused silica optics has been successfully applied in high-power laser system in the field of controllable nuclear fusion. In order to accurately predict the surface topography evolution and to reveal the intrinsic physical mechanism during the process of laser mitigation, experiments of localized CO2 laser mitigation were firstly carried out to analyze the features of mitigated craters under different laser powers. Then a multi-physics coupled mathematical model was developed based on the fluid control equation, heat and mass transfer equation and material phase transition kinetics to investigate the thermodynamic and kinetic behaviors of laser interaction with silica. The model considered the effects of Marangoni convection, gravity, capillary force and vaporization recoil pressure, as well as the nonlinear variation of physical parameters of silica material with respect to temperature. The results showed that with the increase of laser power, the material ablation and the appearance of raised rim occurred simultaneously. The depth of the mitigated crater increased sharply when the threshold for material ablation was attained, while the lateral dimension increased linearly. The vaporization recoil pressure was found to be the dominant factor for the formation of Gaussian crater with the raised rim feature. The capillary force caused the material at the edge of the molten pool to have a tendency to reflow after laser shutting down, but it was too small to change the surface topography. This work could significantly contribute to the understanding of laser mitigation process, which laid the foundation for the accurate prediction and evaluation of surface quality of CO2 laser repaired fused silica surface.

Manufacturing-induced defects have drawn more and more attentions to improve the laser damage resistance performance of KDP crystal applied in high-power laser systems. Here, the morphology of surface scratches on diamond fly-cut KDP crystal is characterized and their effect on the laser damage resistance is theoretically and experimentally investigated. The results indicate that surface scratches could lower laser-induced damage threshold (LIDT) by modulating incident lasers and producing resultant local light intensifications. The induced maximum light intensity enhancement factors (LIEFs) are dependent on scratch shapes and dimensions. The diffraction effects originating from scratch edges are responsible for the strongest light intensification. Even for ultra-precision finished KDP surface with scratches that well satisfy the currently applied scratch/dig specification, the induced LIEFs are quite high, indicating that the actual defect dimension allowance should be amended and specified according to the defect-induced LIEFs. The effect of scratches on laser damage resistance is experimentally verified by the tested LIDT, which is approximately consistent with the simulation one. The morphologies of laser damage sites further confirm the role of scratches in lowering LIDT. This work could offer new perspective and guidance for fully evaluating the performance of ultra-precision manufactured optical materials applied in high-power laser facilities. Keywords: KDP crystal, Manufacturing-induced defects, Diamond fly-cutting, Laser damage resistance performance, Light intensification