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摘要: 深紫外光刻、极紫外光刻和先进光源等现代光学工程需求牵引先进光学制造技术持续发展,要求超光滑光学元件表面粗糙度达到原子级水平以及表面全频段面形误差达到RMS(Root Mean Square)亚纳米量级甚至几十皮米,推动超光滑光学元件制造要求不断逼近物理极限。目前,对于如何实现上述超高精度要求的超光滑加工技术及装备仍然存在技术挑战。尤其对如何实现柱面,椭球面,超环面等复杂曲面的原子量级超光滑加工仍是国内外前沿研究方向。弹性发射加工技术是一种去除函数稳定,超低亚表面缺陷,面向原子级的超光滑加工方法,可以作为加工上述精度要求光学元件的手段。本文总结了弹性发射加工技术的国内外研究现状及最新进展,归纳了弹性发射加工技术的原理,包含流体特性、抛光颗粒运动特性和化学特性,弹性发射加工装备,影响弹性发射加工技术表面粗糙度提升和材料去除效率的因素,分析了弹性发射加工技术面临的问题,展望了未来的发展方向,期望为弹性发射加工技术进一步发展和应用提供一定的参考。Abstract: The requirements of modern optical engineering in fields such as deep ultraviolet lithography, extreme ultraviolet lithography and advanced light sources drive the continuous development of advanced optical manufacturing technology. Modern optical engineering requires the surface roughness of ultra-smooth optical components to reach the atomic level and the surface shape profile error in the full spatial frequency to reach RMS(Root Mean Square) sub-nanometer or even a few dozen picometers. This drives the manufacturing requirements of ultra-smooth optical components to approach the processing limits. At present, there are still technical challenges to achieve the ultra-smooth polishing technology and equipment required for the above ultra-high precision needs. Atomic level ultra-smooth polishing of complex surfaces such as cylinders, ellipsoids and toroids is still a primary direction of research at both domestically and abroad. Elastic emission machining is an atomic-level ultra-smooth processing method with stable removal functionality and ultra-low subsurface defect creation, which can be used for manufacturing optical components with the above-mentioned accuracy requirements. We summarize the research progress of elastic emission machining and equipment at both domestically and abroad, the principles of elastic emission machining which contains fluid characteristics, the movement characteristics of polishing particles and chemical characteristics, the equipment of elastic emission machining, and the factors affecting the improvement of surface roughness and material removal rate of elastic emission machining. Then we analyze the problems faced by elastic emission machining and equipment and look forward to their prospects. It is expected that this paper will provide a reference for the further development and application of elastic emission machining.
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表 1 弹性发射加工技术流体驱动方式[9, 19, 26, 43, 44]
Table 1. Fluid-driven methods of elastic emission machining[9, 19, 26, 43, 44]
Category Polishing tool form Advantage ■ and Disadvantage ● Polishing ball type EEM Spherical ■ It can polish curved optical components.
● It has a low material removal rate and has
side leakage.Ellipsoid ■ Enlarge the interaction area and material
removal rate.
■ The curvature of the tool will change, and
the curved surface can be processed, which is
more suitable for concave components.Polishing wheel type EEM Cylindrical ■ Expand the processing area, improve the
material removal rate and there is no side
leakage.
■ The removal function is linear, and only
planes and cylinders with a single curvature
can be processed.Spherical crown ■ It can polish curved optical components. Nozzle type EEM ■ It is easy to control and can accurately
polish optical components.
■ It is not constrained by the shape of optical
components.表 2 用不同形状的抛光颗粒加工光学表面前后的表面质量和材料去除效率[51]
Table 2. Surface quality and material removal rate of preprocessed and EEM processed surfaces for polishing particles with different shapes[51]
Preprocessed surface Processed using spherical particles Processed using
agglomerated
particlesP-V/nm 2.286 0.9360 1.412 RMS/nm 0.1940 0.0980 0.1410 Material removal rate/(nm·h−1) 1.000 120.00 表 3 影响剪切力的因素
Table 3. Factors affecting shear stress in EEM
Parameter types Factors Processing parameters Liquid film thickness. Applied load Polishing fluid parameters The size, surface morphology, lattice orientation
and incident angle of polishing particles.
Ultrapure water temperature.
The viscosity and concentration of polishing fluidPolishing tool parameters The shape, curvature, speed, surface roughness,
material elastic modulus of polishing toolOptical component parameters The material, lattice orientation,
surface roughness, ripple, geometric
parameters of optical components表 4 参数与剪切力在不同状态下的关系
Table 4. The relationship of parameters with shear stress in different conditions
IR IE VE Polishing tool rotation Negative Positive Positive Polishing fluid viscosity Negative Positive Positive Pressure-viscosity coefficient — — Negative Elastic modulus — Positive Positive Polishing tool radius Positive Positive Positive Load Positive Positive Positive 表 5 弹性发射加工技术在表面粗糙度和材料去除效率方面的研究现状[10, 12, 14, 24, 45, 51, 55]
Table 5. Research status of surface roughness and material removal rates in EEM[10, 12, 14, 24, 45, 51, 55]
Material Surface roughness(RMS) Material removal rate Si 0.080 nm 120 nm/h Zerodur 0.085 nm 1.25×10−3 mm3/h 4H-SiC 0.089 nm − SiC 0.640 nm − Fused silica 0.085 nm − -
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