Liquid-assisted laser ablation has the advantage of relieving thermal effects of common laser ablation processes,whereas the light scattering and shielding effects by laser-induced cavitation bubbles,suspended debris,and turbulent liquid flow generally deteriorate laser beam transmission stability,leading to low energy efficiency and poor surface quality.Here,we report that a continuous and directional high-speed microjet will form in the laser ablation zone if laser-induced primary cavitation bubbles asymmetrically collapse sequentially near the air-liquid interface under a critical thin liquid layer.The laser-induced microjet can instantaneously and directionally remove secondary bubbles and ablation debris around the laser ablation region,and thus a very stable material removal process can be obtained.The shadowgraphs of high-speed camera reveal that the average speed of laser-induced continuous microjet can be as high as 1.1 m s-1 in its initial 500 μm displacement.The coupling effect of laser ablation,mechanical impact along with the collapse of cavitation bubbles and flushing of high-speed microjet helps achieve a high material removal rate and significantly improved surface quality.We name this uncovered liquid-assisted laser ablation process as laser-induced microjet-assisted ablation(LIMJAA)based on its unique characteristics.High-quality microgrooves with a large depth-to-width ratio of 5.2 are obtained by LIMJAA with a single-pass laser scanning process in our experiments.LIMJAA is capable of machining various types of difficult-to-process materials with high-quality arrays of micro-channels,square and circle microscale through-holes.The results and disclosed mechanisms in our work provide a deep understanding of the role of laser-induced microjet in improving the processing quality of liquid-assisted laser micromachining.

Yang Guo;Pei Qiu;Shaolin Xu;Gary J Cheng

School of Mechatronics Engineering,Harbin Institute of Technology,Harbin 150001,People's Republic of China;Department of Mechanical and Energy Engineering,Southern University of Science and Technology,Shenzhen 518055,People's Republic of China;School of Industrial Engineering,Purdue University,West Lafayette,IN 47906,United States of America

极端制造（英文）

[1]Yang Guo;Pei Qiu;Shaolin Xu;Gary J Cheng-.Laser-induced microjet-assisted ablation for high-quality microfabrication)[J].极端制造（英文）,2022(03):115-123

microjet,shadowgraphs,LIMJAA,microgrooves

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