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Publications in Scientific Journals:

S. Bashir, M. Rafique, W. Husinsky:
"Liquid assisted ablation of zirconium for the growth of LIPSS at varying pulse durations and pulse energies by femtosecond laser irradiation";
Nuclear Instruments & Methods in Physics Research Section B, 349 (2015), 230 - 238.



English abstract:
Investigations have been performed to explore the optimized conditions for the growth of Laser Induced
Periodic Surface Structures (LIPSS) by varying pulse durations and pulse energies during ultrashort pulsed
laser ablation of zirconium (Zr). The Ti: Sapphire laser with central wavelength of 800 nm, maximum
pulse energy of 1 mJ is used to ablate Zr targets in the wet environment of ethanol. Scanning Electron
Microscope (SEM) analysis was performed for central as well as the peripheral ablated area to characterize
nano and microstructures formed on the Zr surface. Raman spectroscopy was carried out to explore
the chemical and compositional changes produced in laser ablated Zr. In order to explore the effect of
varying pulse durations ranging from 25 to 100 fs, targets were exposed to 1000 succeeding pulses keeping
the pulse energy constant at 600 lJ. The micrographs of peripheral ablated areas reveal the formation
of nano scale ripples or Laser Induced Periodic Surface Structures (LIPSS) for all pulse durations. LIPSS are
more distinct and well organized for the shortest pulse duration of 25 fs. Whereas, LIPSS become diffused
and indistinct with the increase in the pulse duration. This is the clear indication that shortest pulse duration
(in our case 25 fs) is most suitable for the growth of nanoscale ripples. In order to explore the effect
of varying pulse energies on the growth of LIPSS, targets were exposed to 1000 succeeding pulses with
energies ranging from 200 lJ to 600 lJ for a pulse duration of 25 fs. In the peripheral ablated areas
LIPSS are grown for all pulse energies. For the lowest pulse energy of 200 lJ, LIPSS are distinct and well
defined. For intermediate energies of 300 and 400 lJ they become diffused and indistinct. For higher
pulse energies of 500 and 600 lJ, their appearance again becomes well defined and distinct. For central
ablated areas LIPSS are grown but their appearance diffuses with increasing pulse energies. For the highest
pulse energy they are completely vanished. Raman spectroscopy reveals that in the presence of liquids
the chemical reactivity of the target with liquid is significantly enhanced which is responsible for
the growth of new phases and modification in the chemical composition of the irradiated Zr. The ethanol
forms the carbonyl compounds with the Zr and induces C-C stretching. The reactivity of Zr with oxygen is
responsible for the formation of tetragonal phase and monoclinic phase of zirconia.

Keywords:
Femtosecond laser Pulse duration Pulse energy Nanostructures Laser induced period surface structures

Created from the Publication Database of the Vienna University of Technology.