Femtosecond Pulsed Laser Machining of Fused Silica for Micro-Cavities with Sharp Corners

Fused silica is an important material for applications requiring high temperature resistance, low thermal expansion coefficient, and excellent optical properties. The machining of micro-cavities on fused silica surfaces is of particular interest for micro-fluidic manipulation and miniaturization of high-quality optical waveguides, etc., but it still remains technically challenging for traditional manufacturing techniques. In the present study, machining of square cornered semienclosed micro-cavities on fused silica surfaces by femtosecond laser has been investigated experimentally. The effects of laser machining conditions including laser power, laser scanning speed, laser incidence angle, and laser-off delay time on the sidewall slope and bottom surface roughness of the micro-cavities were comprehensively investigated. The results indicated that laser power played an important role in determining the sidewall slope of the micro-cavity, while the laser scanning speed had a significant influence on the bottom surface roughness and subsurface damage. Furthermore, the sidewall slope of the micro-cavity was linearly increased as the laser incidence angle increases. By using a laser incidence angle of 10 deg and a laser-off delay time of 280 ms, a micro-cavity with sidewall slopes close to right angles (90 deg) was fabricated. This study demonstrates that femtosecond laser machining is an effective method for fabricating sharp cornered micro-cavities in fused silica, and the appropriate selection of laser machining conditions based on practical application scenarios is important.