Water-induced effect on femtosecond laser layered ring trepanning in silicon carbide ceramic sheets using low-to-high pulse repetition rate

Abstract

An underwater femtosecond laser layered ring trepanning (FLLRT) technology is reported in this paper. The FLLRT experiments are performed in silicon carbide (SiC) ceramic sheets in air and water. The effects of water immersion and laser pulse repetition rate on laser trepanning quality and hole generation characteristics are demonstrated by altering the laser pulse repetition rate. The underwater FLLRT technology notably improves the laser hole-trepanning quality for the SiC material because of the water cooling–insulating effect, underwater bubble-cavitation effect, and water microstreaming effect. Performing FLLRT in water, the hole diameter, particularly the hole exit diameter, increased whereas the hole taper decreased when using a relatively low pulse repetition rate. Furthermore, the hole-wall formation quality and surface uniformity improved while notably reducing the hole-wall oxidation. Significantly, the redeposition of the vapourised material and the resolidification of the molten material are greatly reduced, thereby reducing the formation of the recast layer and micro cracks. When the pulse repetition rate was relatively high, the local thermal accumulation effect induced by significantly more successive laser pulses was notably enhanced for melting the SiC material despite the laser ablation-induced vapourisation.