In situ observation of phase-locking growth of LIPSS promoted by random deposits or pre-formed nano/microstructures on a SiC single crystal

Abstract

In recent years, real-time microscopic imaging of laser-induced periodic surface structure (LIPSS) formation during laser micromachining was found to be favorable for investigating the physical origin of the LIPSS on various materials. In this paper, an ultraviolet-oblique-illumination high-resolution microscopic imaging setup, combined with a focal spot enlarging technique, was used for observing the initiation, development, and maturation of the LIPSS. The research focuses on the influence of random surface deposits, laser-etched microtrench, and pre-existing ripples on laser-induced LIPSS under pulse-by-pulse irradiation. Compared to the flat region on the SiC surface, both random surface deposits and the microtrench promote the phase-locking growth of the LIPSS, but in different ways. The finite-difference time-domain method shows that random surface deposits may promote the LIPSS growth through the action of the interference field of incident light with its scattered light on deposits. A microtrench covered with high-spatial-frequency LIPSS may assist LIPSS growth by absorption enhancement-induced easier transferring of the incident periodic field. Finally, phase-locking growth of the LIPSS was found to be the result of the light-trapping effect of high-refractive-index sidewalls of the LIPSS valley. Our results showed that local morphologies were very important in LIPSS formation.