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Umm-I-Kalsoom, S. Bashir, N. Ali, M. Rafique, W. Husinsky, C. Nathala, S. Makarov, N. Begum:
"Effect of fluence and ambient environment on the surface and structural modification of femtosecond laser irradiated Ti";
Chinese Physics B, 25 (2016), 0181011; 0181017.

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.

LIPSS, ablation threshold, incubation coefficient, structural modification