Abstract
We study the evolution of periodic nanostructures formed on the surface of diamond by femtosecond laser irradiation delivering 230 fs pulses at 1030 nm and 515 nm wavelengths with a repetition rate of 250 kHz. Using scanning electron microscopy, we observe a change in the periodicity of the nanostructures by varying the number of pulses overlapping in the laser focal volume. We simulate the evolution of the period of the high spatial frequency laser induced periodic surface structures at the two wavelengths as a function of number of pulses, accounting for the change in the optical properties of diamond via a generalized plasmonic model. We propose a hypothesis that describes the origin of the nanostructures and the principal role of plasmonic excitation in their formation during multipulse femtosecond laser irradiation.
Highlights
Laser–induced periodic surface structures (LIPSS) have attracted considerable attention by researchers, as indicated by the growth in the number of papers published on the topic in recent years.[1]
Diamond surface excitation by femtosecond laser pulses builds up a thin pseudo-metal layer[27] due to the non-thermal melting which takes place at sub-vibrational time scale, since the pulse duration of the femtosecond laser is lower than the electron-phonon relaxation time.[27,28,29,30,31]
We show the importance of the plasmonic excitation on the formation of the high spatial frequency LIPSS (HSFL), and shed insight into other physical processes involved
Summary
Laser–induced periodic surface structures (LIPSS) have attracted considerable attention by researchers, as indicated by the growth in the number of papers published on the topic in recent years.[1]. LIPSS formation is a universal phenomenon and has been observed in dielectrics, semiconductors, metals and polymers.[1,6] Generally, two types of ripples can be observed during the irradiation by multipulse femtosecond laser, low spatial frequency LIPSS (LSFL) and high spatial frequency LIPSS (HSFL). Derrien et al.[10] used an above ablation threshold fluence where the critical density of plasmonic excitation is achieved with the first femtosecond laser pulse. They observed ablation in the middle of the laser spot surrounded by LSFL and at the edge where the fluence is low, they found the HSFL. We suggest that this repartition of the two kinds of LIPSS observed within the same volume spot laser are the result of different physical mechanisms
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