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Material surfaces irradiated with laser radiation under specific conditions can lead to laser-induced periodic surface structure (LIPSS) formation. The formation of these surface structures is a robust one-step method that allows for high throughput and cheap surface nano-structuring with spatial periods that can be greatly lower than the irradiating laser wavelength. Typically, a structural size ranges from several micrometers down to less than 100 nm and the structures strongly correlate with the polarization direction of the light used for their formation.
The regularity of LIPSS formation depends on various laser and material parameters. Some metals can exhibit highly regular LIPSS (HR-LIPSS) when the correct conditions are met. One of the main drawbacks of precise LIPSS texturization is the difficulty in controlling the ripple quality. Thus, understanding the processes which lead to HR-LIPSS formation is one step in making laser-based material texturization more prevalent.
The aim of this research was to create highly regular surface structures and investigate how the ripple formation depends on various laser and material properties. The experiment was carried out using femtosecond laser systems. Different laser harmonics modules were used for the LIPSS formation to cover both the IR and UV wavelengths.
Structures were formed on various steel, copper, aluminum, and titanium samples employing different laser wavelengths, pulse energies, pulse overlaps, and polarizations. The resulting surface structures were then examined both visually and with the help of a scanning electron microscope (SEM). LIPSS images taken by SEM were then digitally processed to calculate the distribution of LIPSS orientation angle (DLOA) which characterizes the regularity of the surface structures.
We show that by using ultraviolet femtosecond laser sources, choosing the right pulse energy, pulse overlap values, and sufficiently sharp focusing lens, HR-LIPSS can be formed on metals for which highly regular ripples don’t form using infrared laser radiation.
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