Research On Femtosecond Laser Purse Polishing Of Silicon Carbide Ceramic Material

After the materials of silicon, germanium and arsenic, a kind of newly developed semiconductor material that belongs to the third generation—Silicon carbide appeared. For its high stiffness and thermal stability, etc, it has become the best choice for machining high precision space mirror. Also in the field of space optics and electronics and making micro-structure molds, silicon carbide has a very great application prospect.As a multi-phase ceramic with high hardness and brittleness, silicon carbide is a typical difficult to machine material. The method of machining silicon carbide with high efficient and precision is a processing problem. Laser polishing technology is a new surface processing technology that developed in recent years. Ultra-short pulse laser polishing is a very good method to machine hard and brittle materials, not only for its high efficiency and high precision, but also for a very small heat affected zone.In this paper, the polishing mechanism and process of silicon carbide with femtosecond pulse laser were researched from the polishing system construction, experimental design, experimental implementation to data analysis and processing, etc. Polish silicon carbide with femtosecond pulse laser(λ=800nm, f=1kHz). The surface topography and surface roughness were detected by laser confocal microscopy and scanning electron microscopy. Analysis the effect of laser pulse energy, spot overlap (scan speed, hatch), the laser incident angle and other factors on the femtosecond pulse laser polishing process and machined quality.First, do experiments with femtosecond pulse laser (pulse width 50fs, pulse repetition rate 1 kHz), obtained the laser ablation threshold of silicon carbide 0.23J/cm², the radius of focusing spot waist 31μm. Detect and analysis the surface morphology of the polished area with scanning electron microscopy. Found that with Gaussian laser beam irradiation, different ablation morphology appeared from the center to the edge of the ablation spot. And at the edge of the ablation spot, there appeared a kind of microstructure with regular directions, and there also appeared some granular SiO₂ oxide.Second, polish silicon carbide with different laser purse energy density, spot overlap and laser incident angle in the air. Found that with the same other parameters, the silicon carbide surface roughness after polishing can be smaller with laser pulse energy density increase at a certain range; Improve the laser beam overlap and increase the laser incident angle also can make the polished surface roughness smaller.