Femtosecond laser ablation of Zn in air and ethanol: effect of fluence on the surface morphology, ablated area, ablation rate and hardness

This paper reports the effect of Ti:Sapphire laser (800 nm, 30 fs) fluence on the surface morphology, ablated area, ablation rate and hardness of a femtosecond laser irradiated Zn in air and ethanol. Targets were exposed to 1000 succeeding pulses at various fluences ranging from 1.3 to 5 J cm−2. To characterize the growth of structures on the surface of irradiated Zn, Field Emission Scanning Electron Microscopy (FESEM) has been performed. The ablation depth has been measured using a confocal microscope. Nonuniform surface morphology with an appearance of both micro and nanoscale droplets, particulates and rims has been observed in case of air-assisted ablation, whereas, in ethanol, nanoscale colloids, droplets, pores and bowl-shaped cavities have been formed. The ablation of Zn in air is responsible for deep craters with pronounced melt expulsions and ripples. Whereas, shallow and clean craters are formed in ethanol. The ablation threshold fluence is evaluated analytically and experimentally by employing three methods, i.e., squared diameter, depth ablation rate, and volume ablation rates. The hardness of irradiated targets is higher as compared to untreated Zn and shows an increasing trend with increasing fluence for both environments. However, in the case of ethanol, the hardness values are higher than air.