Effect of fluence and ambient environment on the surface and structural modification of femtosecond laser irradiated Ti

Under certain conditions, ultrafast pulsed laser interaction with matter leads to the formation of self-organized conical as well as periodic surface structures (commonly reffered to as, laser induced periodic surface structures, LIPSS). The purpose of the present investigations is to explore the effect of fsec laser fluence and ambient environments (Vacuum & O₂) on the formation of LIPSS and conical structures on the Ti surface. The surface morphology was investigated by scanning electron microscope (SEM). The ablation threshold with single and multiple (N=100) shots and the existence of an incubation effect was demonstrated by SEM investigations for both the vacuum and the O₂ environment. The phase analysis and chemical composition of the exposed targets were performed by x-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDS), respectively. SEM investigations reveal the formation of LIPSS (nano & micro). FFT d-spacing calculations illustrate the dependence of periodicity on the fluence and ambient environment. The periodicity of nano-scale LIPSS is higher in the case of irradiation under vacuum conditions as compared to O₂. Furthermore, the O₂ environment reduces the ablation threshold. XRD data reveal that for the O₂ environment, new phases (oxides of Ti) are formed. EDS analysis exhibits that after irradiation under vacuum conditions, the percentage of impurity element (Al) is reduced. The irradiation in the O₂ environment results in 15% atomic diffusion of oxygen.