多脉冲飞秒激光烧蚀铝靶动态特性研究

利用时间分辨阴影图研究了脉冲能量在200微焦的多脉冲飞 秒激光烧蚀铝靶的动态过程、并使用 扫描电镜研究了靶材表面烧蚀区域的形貌特征。时间分辨阴影图的记录结果表明,在不同时 间延迟条件 下,飞秒激光烧蚀铝靶形成的冲击波体积和喷射物的空间分布均随着脉冲个数的增加而发生 不同程度的变 化,尤其是单脉冲烧蚀情况下在1ns延时阴影图中观察到的近同心圆条纹会随着脉冲数目增 加逐渐变得模 糊乃至消失。烧蚀区的电子扫描显微镜图像清楚地揭示出烧蚀过程中伴随有液态铝的产生, 其溅射凝固后 在靶材表面形成小球和细丝状微纳结构。实验结果进一步证实了由前序脉冲烧蚀导致的铝靶 表面结构的改 变会对后继脉冲的烧蚀产生显著影响,从而使多脉冲烧蚀表现出明显不同于单脉冲烧蚀的特 性。这些结果 对飞秒激光脉冲沉积薄膜、直写生成表面微结构等应用的工艺参数优化具有很好的指导意义 。

Study of dynamic process in multiple pulses ablation of aluminum by femtosecond laser

Ablation of aluminum target by multipl e femtosecond laser pulses is investigated by recording the time-resolved shado wgraphs of the dynamic ablation process.The scanning electron microscopic (SEM) measurements of the ablation sites are performed to analyze the surface morphology and its in fluence on the ablation process.With the help of shadowgraphs recorded at different time delays,it is fo und that the spatial distribution of the ejected material and the expansion of the shock wave generated during the ablation vary noticeably with the number of laser pulses.For the initial one or two pulses,nearly concentric a nd semicircular stripes within the shock wave front are observed at 1ns delay time.For subsequent pulses,howev er,such stripes become blurred and almost invisible.The SEM images of the ablation sites reveal some m icro- and nano-structures formed by condensed aluminum droplets and molten streams generated through laser ablation.Ablation by multiple femtosecond pulses exhibits different characteristics compared with the case by a single femtosecond pulse,which is primarily due to the surface morphology change induced by the pr eceding pulses on the target surface.These results should provide a meaningful guideline in applications of femtosecond laser such as pulsed laser deposition and micro-machining by direct laser writing.