Abstract
The self-organized formation of nanoscale laser-induced periodic surface structures (LIPSS) is still not fully understood with respect to the dynamics and interplay of contributing complex mechanisms. The transition from randomness to order and the specific role of nano-feedback are of fundamental interest because of their general aspects. In our study, the very first steps of the surface reconfiguration are demonstrated by analyzing the topology of evolving nano-crater maps. The evolution of spatial frequencies and directional arrangement indicate a feedback-driven adaptation of k-vectors to the required excitation conditions of elementary dipoles in the linearly polarized laser field. The time-dependent structure formation was studied by pump-probe diffraction and scattering experiments. The ratio of the contributions of characteristic light patterns enables plasmonic and non-plasmonic mechanisms to be distinguished, which subsequently act at distinctly different time scales. Recently developed multistage models for the dynamics of material modification are confirmed. The influence of accumulation effects is clearly demonstrated by characteristic changes in scattering and diffraction with an increasing number of preceding pulses. It is assumed that the thermal and plasmonic contributions to accumulation are coupled and thus generate spatially variable modifications.
Highlights
After the invention of the laser, it was reported by Milton Birnbaum that the illumination of semiconductor surfaces with intense laser radiation can lead to the generation of grating-like structures in solid surfaces [1]
The spatial and temporal coincidence of pump and probe beams was roughly pre-adjusted by detecting the non-collinear (SHG) intensity cross-correlation signal generated by a second barium borate (BBO) crystal with a photodiode
The dynamics of femtosecond-laser-induced ripple formation in silicon surfaces was studied with particular emphasis on structural changes and feedback
Summary
After the invention of the laser, it was reported by Milton Birnbaum that the illumination of semiconductor surfaces with intense laser radiation can lead to the generation of grating-like structures in solid surfaces [1]. Thermal material modification and rearrangement were detected at different time scales compared to the exciting light pulses, the ripple formation is significantly influenced by plasmons initially induced by the ultrafast laser pulses [39]. These findings indicate that a combination of sub-surface bubble generation and plasmon-related spatially periodical energy insertion results in the generation of isolated or merged nanovoids, depending on the fluence. Systematic pulse-number-dependent measurements emphasize the role of feedback and accumulation effects for the self-organizing emergence of periodic nanostructures in silicon surfaces
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