High-spatial frequency periodic structures induced on Ti surface by femtosecond laser pulses

This paper reports the formation of different periodic structures on Ti surface irradiated by 800 nm femtosecond laser pulses in air and water.In air, low spatial frequency periodic structures with period of 500-560 nm are obtained with high laser fluence irradiation; high spatial frequency periodic structures with period of 220-340 nm are obtained with low laser fluence irradiation.All of them are perpendicular to the laser polarization and the period of the structures increases with pulse numbers.In water, not only high spatial frequency periodic structures (215-250 nm) with direction perpendicular to the laser polarization are obtained, but also high spatial frequency periodic structures (about one eighth of laser wavelength) with direction parallel to the laser polarization are obtained.Combined with the surface plasmon polaritons, second harmonic generation and the Sipe model to interpret different periodic structures formation mechanism, we found that the formation of periodic structures is related to the titanium oxide layer.