High Efficient machining of Fresnel Microstructure on Silicon Carbide Using Picosecond Laser Ablation

摘要

Fresnel micro-structured lens has been widely used in solar energy and advanced optical systems because of its small size and excellent optical performance.In order to achieve the mass production of Fresnel lens, glass molding press (GMP) technology has been proposed.Silicon carbide (SiC) is a typical heat-resisting and low-expandation material and suits for using as GMP moulds.Traditionally, SiC moulds production process mainly consists of ultra-precision grinding and polishing.However, the high hardness and brittleness of SiC have caused rapid wear on grinding wheel, thus limited the improvement of accuracy and production efficiency of SiC micro-structured moulds.Picosecond laser machining has the advantages of determined ablation threshold, low thermal damage, high material removal rate (MRR) and relatively low costs, which has showed great potential in the field of micro-machining of hard and brittle materials.In this paper, a picosecond laser device was attached on an ultra-precision machine tool and used to fabricate Fresnel micro-structured surface on SiC.Variable laser scanning feedrate was adopted to generate different material removal depth at different radius position according to the discontinuous profile shape of Fresnel microstructure.The final experiment results showed that the SiC moulds machined by picosecond laser could achieve high MRR (0.326 mm3/min), profile form error below 10 μm,subsurface damage depth below 5 μm.Overall, this research had developed a new solution for the production of Fresnel micro-structured moulds and expanded the application fields of picosecond laser.