Abstract: Laser polishing is a non-contact ultra-precision polishing method for equal materials. The evolution of the “trident” surface morphology observed in experiments cannot be explained by the traditional theory of surface tension and Marangoni effect dominant molten pool flow. It is found that the plastic deformation plays a critical role in surface topography evolution. The residual stress is measured by XRD and the section is observed by TEM, which shows that the plastic deformation occurs before the material melts in laser polishing. Considering plastic deformation before melting, and surface tension, Marangoni effect after melting, the “trident” surface topography of the center bulge and the edge piling up after single point laser polishing is investigated. Based on this premise, the surface morphologies affected by plastic deformation are analyzed at different scanning intervals. When the scanning intervals are less than 2.5 μm, the central bulge caused by plastic deformation can be polished by subsequent laser pulses, and the surface roughness of monocrystal silicon decreases from 4.04 nm to 0.34 nm. The evolution law and mechanism of surface topography under the plastic deformation and capillary flow in laser polishing are summarized, which provides theoretical guidance for parameter selection of laser polishing.

Key words: laser polishing, plastic deformation, topography evolution, ultra-precision machining