Time-resolved shadowgraphs and morphology analyses of aluminum ablation with multiple femtosecond laser pulses**Project supported by the Science and Technology Development Fund Planning Project for the Universities of Tianjin, China (Grant No. 20140902), the Natural Science Foundation of Tianjin City, China (Grant No. 16JCQNJC01900), the National Natural Science Foundation of China (Grant Nos. 51376136 and 61474082), and the Science and Technology

Abstract

Aluminum ablation by multiple femtosecond laser pulses is investigated via time-resolved shadowgraphs and scanning electron microscope (SEM) images of the ablation spot. The spatial distribution of the ejected material and the radius of the shock wave generated during the ablation are found to vary with the increase in the number of pulses. In the initial two pulses, nearly concentric and semicircular stripes within the shock wave front are observed, unlike in subsequent pulses. Ablation by multiple femtosecond pulses exhibits different characteristics compared with the case induced by single femtosecond pulse because of the changes to the aluminum target surface induced by the preceding pulses.