帮我翻译一篇科技文本从中文到英文：1引言熔石英玻璃作为典型的宽禁带介质材料广泛应用于制造光栅、真空窗口、屏蔽片和透镜等器件。为了实现高精度熔石英玻璃的批量制造国内外普遍采用磨削成形→精密研磨→超精密抛光的工艺流程。其中抛光加工作为光学材料精密超精密制造工序的最后一个步骤对元件的加工质量和表面完整性有着重要作用。传统的化学机械抛光技术通过化学能和机械能的耦合作用获得光洁平整的表面但由于工件在加工过程

1. Introduction Fused silica glass is a typical wide-bandgap dielectric material, which is widely used in the production of devices such as gratings, vacuum windows, shielding plates, and lenses. In order to achieve mass production of high-precision fused silica glass, the process of "grinding shaping → precision grinding → ultra-precision polishing" is commonly used domestically and internationally. Among them, polishing is the last step in the process of precision/ultra-precision manufacturing of optical materials, and plays an important role in the processing quality and surface integrity of components.

Traditional chemical-mechanical polishing technology obtains a smooth and flat surface through the coupling effect of chemical energy and mechanical energy. However, due to the normal cutting action of abrasive particles during the processing of the workpiece, it is easy to produce mechanical defects such as scratches, micro cracks, or pits below the surface, which can easily induce material melting and explosive damage under strong laser irradiation. In recent years, the magnetic-assisted polishing technology that uses fluid dynamic pressure shearing to remove materials has received widespread attention from scholars at home and abroad, and has gradually developed into a processing method for "near-zero" defect surfaces of high-power optics. According to the different magnetic particles (micron-sized iron powder or nano-sized iron oxide) in the polishing fluid, the magnetic-assisted polishing technology is mainly divided into three types: magnetorheological fluid (MRF), magnetic fluid (MF), and magnetic composite fluid (MCF) polishing. Magnetic-assisted polishing uses magnetic particles, non-magnetic abrasive particles, cellulose, and deionized water to form a viscous semi-solid flexible polishing head, and the abrasive particles under the polishing head come into contact with the workpiece, undergo relative motion and micro-cutting to achieve low damage and high precision polishing. Shi et al. analyzed the feasibility of elastic MRF polishing based on the theory of elastic-plastic deformation, and achieved chemical-dominant elastic MRF polishing of large-diameter fused silica glass by changing the composition of magnetorheological fluid and polishing parameters, ultimately obtaining a super-smooth surface with a roughness Ra of 0.167nm. Jiang et al. compared the differences in the normal polishing force, tangential polishing force, material removal rate, and surface roughness of the workpiece during traditional MCF polishing and ultrasonic-assisted MCF polishing. The results showed that ultrasonic-assisted polishing is beneficial to improving the material removal rate and surface smoothness of the workpiece. Guo et al. showed that the material removal rate of BK7 glass during end-face MCF polishing is positively correlated with the speed of the carrier disk, negatively correlated with the polishing gap, and established a material removal rate model related to tangential force and normal force of the workpiece. The above research has studied the material removal mechanism and surface quality formation mechanism of magnetic-assisted polishing technology from both theoretical and experimental aspects, and promoted the application of magnetic-assisted processing technology in the field of optical manufacturing.

In this paper, different magnetic polishing fluids with different polishing gaps and different iron powder volume ratios were used to perform magnetic-assisted polishing on fused silica elements for different times, and the material removal rate, surface roughness, and transmittance of fused silica were analyzed and evaluated. Combined with the simulation calculation of spatial magnetic induction intensity, the influence of spatial magnetic induction intensity and iron powder volume ratio on material removal efficiency and surface quality is clarified, and the polishing process of "small polishing gap + high iron powder ratio polishing fluid → large polishing gap + low iron powder ratio polishing fluid" is proposed, providing theoretical basis and technical support for efficient and low-defect processing of high-power laser elements.

2. Experiment 2.1 Sample Preparation In this experiment, magnetic-assisted polishing was performed on fused silica glass elements using a self-built circular polishing machine. The polishing equipment is shown in Figure 1. The horizontal main spindle drives a ring-shaped neodymium-iron-boron (Nd-Fe-B) magnet with a magnetic flux density of 0.4T to rotate at a speed of nt, forming a spatial dynamic magnetic field. A ring-shaped polylactic acid (PLA) baffle is installed on each end face of the magnet, which has the same outer diameter of 40mm and inner diameter of 25mm, and thickness of 8mm and 4mm, respectively. The ring-shaped baffle and ring-shaped magnet jointly form a polishing wheel, and there is a polishing gap δ between the polishing wheel and the workpiece below it. A 40mm × 40mm × 5mm fused silica glass was used as the processing object, and the workpiece was double-sided ground with W5-W10 silicon carbide before polishing, with an initial surface roughness Ra of 0.2-0.25μm and sub-surface crack depth within 4.5μm