Repetition rate and pulse energy effects on LIPSS formation in metal-coated glass under UV femtosecond irradiation
摘要
Formation of laser-induced periodic surface structures (LIPSS) on metal thin films deposited on soda-lime glass is investigated using a femtosecond (fs) laser source with third harmonic generation (THG) producing a 343 nm UV beam. In this study, a bilayer of chromium (30 nm) and silver (100 nm) was chosen as metal thin films, sputtered onto a glass substrate to enhance the UV light absorption on the dielectric material surface. The variation in repetition rate (f) and pulse energy (E) of the laser irradiation was investigated while process time is fixed to 1 s, with parameters ranging from 10 kHz to 250 kHz and the pulse energy increasing from 1.5 µJ to 3 µJ. The experimental observation reveals the formation of LIPSS on both metal films and dielectric glass substrates exhibiting low spatial frequency LIPSS (LSFL) upon irradiation with linearly polarized femtosecond laser pulses (τ = 300 fs at 1030 nm) in air environment. With the pulse energy of 1.5 µJ, and for all frequencies, no surface modification was observed. When the pulse energy was increased to 2.2 µJ with a 100 kHz repetition rate, the bilayer metal films were ablated, and LIPSS were formed on the dielectric glass substrate at the center of the laser spot, oriented perpendicular to the laser beam polarization. Spatial period of LSFL⊥ on glass is about 240 nm where the the spatial period of the LSFLII on silver reach 330 nm therefore, around the value of the wavelength of the incident UV wavelength (343 nm). Upon increasing f to 250 kHz and energy to 3 µJ, the glass surface undergoes texturing or ablation due to elevated threshold fluence and the higher number of pulses achieved.