Subwavelength LIPSS formation on SS304 by picosecond laser irradiation under water confinement

Highlights: • ps-laser irradiation generated LIPSS on a SS-304 immersed in water confinement. • Tunable LIPSS periodicity was observed due to the pulse repetition rate modification. • Hierarchical structures formation after multiple impact pulses with high overlap. • Hydrophobicity surface sample enhance as an outcome of laser processing. Laser induced periodic surface structures were generated in a single step by applying picosecond laser irradiation at different repetition rates on a surface area of 15 × 15 mm² of a stainless steel-304 probe immersed in a confinement liquid medium and on ambient air. Periodicity modification from high to low spatial surface frequency LIPSS was observed by modifying the pulse repetition rate from 1.3 to 402 kHz at a constant fluence (7 J/cm²) under water confinement. Additional experiments at lower fluences (1.78 and 5.33 J/cm²) were performed to evaluate the periodicity under water confinement. Wettability analysis of the processed area yielded significative changes on the drop contact angle showing a wetting transition from hydrophilicity to hydrophobicity of the samples surface treated by multiple impact pulses under water confinement.