Acoustic limitations on the efficiency of machining by femtosecond laser-induced optical breakdown

摘要

The authors find an unexpected strong influence of acoustic phenomena on the efficiency of water-assisted femtosecond laser nanomachining. Analysis of acoustic interactions across a metastable structure of two phase flow in a nanocapillary, predicts acoustic nodes that strongly limit machining efficiency. Strategies for fabrication of high aspect ratio channels (>1000) are identified: increasing the speed of acoustic transmission delays formation of nodes, and can be accomplished by maximizing hydrogen in the gas phase or by varying pressure. These results reveal that laser machining can be strongly limited by acoustic phenomena not previously considered in the analysis of optical breakdown.