Influence of thin film for LIPSS formation on soda-lime glass using SHG femtosecond laser beam

Abstract

This investigation focuses on the influence of thin films on laser-induced periodic surface structures (TF-LIPSSs) formed on soda-lime glass using femtosecond laser pulses with a wavelength of 515 nm. In this study, we introduce a new framework involving a combined metal thin film of chromium and silver (Cr:30 nm + Ag:100 nm) deposited onto soda-lime glass by DC magnetron sputtering. Due to their better coupling by heat accumulation, metal thin film enables a more efficient transfer of energy to the dielectric glass substrate, leading to the formation of periodic structures. The thin-metal-film-deposited glass substrate is irradiated with the second-harmonic generator of a Satsuma laser source to create the LIPSS at high repetition rates ranging from 10 to 250 kHz. We observe simultaneously low-spatial-frequency LIPSS (LSFL) with a spatial period (Λ) of 400 nm and high-spatial-frequency LIPSS (HSFL) with a spatial period of about 110 nm on thin film and glass substrate, respectively. Interestingly, at 10 μJ and 100 kHz, the HSFL observed on the glass substrate are significantly smaller than half of the irradiation wavelength. In the center region, the HSFL⊥ are perpendicular to the laser beam polarization. In the transitioned region between the impact center and the melted area, the HSFLII are parallel to the polarization. Furthermore, when the energy was increased from 10 to 15 μJ, the irradiated zone geometry changed from a regular circular shape to an elliptical one due to an uneven energy distribution over the ablated area, resulting in the formation of irregular surface structures. Finally, a comparative analysis of surface modifications on a metal thin-film-coated glass substrate using different repetition rates and energy levels revealed dissimilar morphological structures.