Formation of Nano- and Micro-Scale Surface Features Induced by Long-Range Femtosecond Filament Laser Ablation

In this work, we study the characteristics of femtosecond-filament-laser-matter interactions and laser-induced periodic surface structures (LIPSS) at a beam-propagation distance up to 55 m. The quantification of the periodicity of filament-induced self-organized surface structures was accomplished by SEM and AFM measurements combined with the use of discrete two-dimensional fast Fourier transform (2D-FFT) analysis, at different filament propagation distances. The results show that the size of the nano-scale surface features increased with ongoing laser filament processing and, further, periodic ripples started to form in the ablation-spot center after irradiation with five spatially overlapping pulses. The effective number of irradiating filament pulses per spot area affected the developing surface texture, with the period of the low spatial frequency LIPSS reducing notably at a high pulse number. The high regularity of the filament-induced ripples was verified by the demonstration of the angle-of-incidence-dependent diffraction of sunlight. This work underlines the potential of long-range femtosecond filamentation for energy delivery at remote distances, with suppressed diffraction and long depth focus, which can be used in biomimetic laser surface engineering and remote-sensing applications.

Automated summary

This work investigates the interactions between femtosecond filament lasers and matter, as well as the formation of laser-induced periodic surface structures (LIPSS) at a beam-propagation distance of up to 55 m. The study quantifies the periodicity of filament-induced self-organized surface structures and demonstrates that the size of nano-scale surface features increases with ongoing laser filament processing. In addition, periodic ripples start to form in the center of the ablation spot after irradiation with five spatially overlapping pulses. The results also show that the number of irradiating filament pulses per spot area significantly affects the surface texture development, with the period of low spatial frequency LIPSS reducing notably at a high pulse number. The high regularity of the filament-induced ripples is verified through the angle-of-incidence-dependent diffraction of sunlight. This work highlights the potential of long-range femtosecond filamentation for energy delivery at remote distances, with suppressed diffraction and long depth focus, and its applications in biomimetic laser surface engineering and remote sensing.