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S. Bashir, M. Rafique, C. Nathala, W. Husinsky:
"Surface and structural modifications of titanium induced by various pulse energies of a femtosecond laser in liquid and dry environment";
Applied Physics A: Materials Science & Processing, 114 (2014), 243 - 251.

The surface and structural modification of
titanium (Ti) has been explored after the interaction of
ultrashort laser pulses with the surface target. The targets
were exposed by femtosecond Ti: Sapphire laser pulses in
liquid (ethanol) and dry (air) environment. In order to
explore the effect of pulse energy, the targets were exposed
to 1,000 succeeding pulses for various pulse energies
ranging from 200 to 500 lJ for pulse duration of 25 fs.
SEM analyses were performed for central as well as the
peripheral ablated areas of the target. It was found that in
the case of ethanol (both for central and peripheral ablated
areas) there is a grain growth along with nanoscale pores
and dots when the target was irradiated for 200 lJ. For
intermediate energies (300-400 lJ), grains of 1-2 lm with
distinct boundaries are formed in the central ablated area.
Whereas in the peripheral ablated area, laser-induced
periodic surface structures (LIPSS) and globules are
grown. For the highest pulse energy (500 lJ), distinct
grains are observed for both regions. However, in the
peripheral area the grains are of bigger size with cracks
along the boundaries. In case of ablation in air, in the
center of ablated areas, island-like structures with multiple
ablative layer or LIPSS and nanoscale spheres are observed
both for lower and intermediate pulse energies. For the
highest pulse energy only nanoscale LIPSS could be
observed. For ablation in air at the peripheral areas, welldefined,
laser-induced periodic surface structures are
observed for all pulse energies. Raman spectroscopy
reveals that the liquid (ethanol) environment forms the
carbonyl compounds with the metal and induces C-C
stretching vibration, whereas in case of air, hydroxo complexes
are formed. It has been found that surface treatment
of Ti with ultrashort (25 fs) laser radiation in ethanol
environment allows the growth of particular surface
structures in the form of grains and simultaneously induces
changes in its chemical composition.