Wavelength-dependent correlation of LIPSS periodicity and laser penetration depth in stainless steel

This research paper delves into the exploration of laser-induced periodic surface structures (LIPSS) on a 100 µm thin stainless steel (SS) sheet. Through the application of laser irradiation with wavelengths spanning from 400 to 2400 nm, we systematically generate ladder-like LIPSS across a substantial area, incorporating LIPSS with both low spatial frequency (LSFL) and high spatial frequency (HSFL) simultaneously. Notably, the embedded LIPSS exhibit a linear relationship in the observed spatial periodicity of LSFL and HSFL with wavelengths up to 2000 nm, after which a decrease in periodicity is observed. By employing cross-sectional electron microscopy, we scrutinize the penetration depth of laser radiation or laser-affected zone, in the LIPSS-formed SS sheets, revealing a parallel trend with LSFL and HSFL spatial periodicity. Specifically, the penetration depth increases with wavelength up to 2000 nm, reaching a peak at approximately 13 µm, and subsequently decreases. This distinctive correlation underscores the role of plasma material reorganizational effects in LIPSS formation at higher wavelengths, presenting a new experimental observation to the existing literature. The findings enhance our comprehension of laser-material interactions and hold potential implications for surface engineering and material science applications.