Pulse duration and environmental effects on the surface nanostructuring and mechanical properties of zinc during femtosecond laser irradiation

Abstract

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 J 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.