This paper reports on the effect of both the pulse duration and environments on the surface morphology, ablated area, ablation rate, and mechanical properties of a femtosecond laser irradiated zinc (Zn) in air and ethanol. The targets were exposed to 1000 succeeding pulses of Ti:sapphire laser (800 nm) at a fluence of ${2.5}\;{\rm{J}}\;{{\rm{cm}}^{- 2}}$ with various pulse durations ranging from 30 to 550 fs. The surface structures have been characterized by a field emission scanning electron microscope, whereas the ablation rate has been measured using confocal and optical microscopy. The mechanical behavior of irradiated targets has been explored by using a microhardness tester. It is observed that in the case of Zn ablation in air, a crater with nonuniform surface morphology along with formation of both micro- and nanoscale droplets rims, organized laser-induced periodic surfaces are observed, whereas in the case of ablation in ethanol, nano- and microscale scale droplets, pores, cones, agglomerates, and channels are formed. The growth and the shape of these structures are strongly dependent on the pulse durations and environments. The hardness of laser-treated samples is found to be higher as compared to untreated ones and is also found higher for liquid-assisted ablated Zn as compared to air-assisted ablated targets due to an increased chemical reactivity in an ethanol-confined environment. The decreasing trend of hardness with increasing pulse duration for both environments is observed, which is attributed to decreasing trend in both shock pressure and ablation pressure with increasing pulse duration.

中文翻译：

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飞秒激光辐照期间的脉冲持续时间和环境效应对锌的表面纳米结构和力学性能的影响

本文报道了脉冲持续时间和环境对飞秒激光辐照空气和乙醇中的锌（Zn）的表面形态，烧蚀面积，烧蚀速率以及机械性能的影响。目标以$ {2.5} \; {\ rm {J}} \; {{\ rm {cm}} ^ {-2}}的通量曝光到1000个连续的Ti：蓝宝石激光（800 nm）脉冲。$具有30至550 fs的各种脉冲持续时间。表面结构已通过场发射扫描电子显微镜进行了表征，而消融率已使用共聚焦和光学显微镜进行了测量。已通过使用显微硬度测试仪探索了辐照目标的机械行为。观察到，在空气中进行Zn烧蚀的情况下，观察到具有不均匀表面形态的火山口，同时形成了微米级和纳米级的液滴边缘，观察到有组织的激光诱导的周期性表面，而在乙醇中进行烧蚀的情况下，则观察到纳米-并形成微尺度的液滴，孔，锥体，团聚体和通道。这些结构的生长和形状在很大程度上取决于脉冲的持续时间和环境。发现激光处理的样品的硬度与未处理的样品相比更高，并且由于在乙醇限制的环境中化学反应性的提高，与空气辅助的烧蚀靶材相比，液体辅助的烧蚀锌的硬度也更高。在两种环境下都观察到硬度随着脉冲持续时间的增加而下降的趋势，这归因于冲击压力和消融压力随脉冲持续时间的增加而下降的趋势。