Effect of surface roughening on femtosecond laser-induced ripple structures

The effect of surface roughness was studied on the formation of femtosecond laser-induced ripple structures for 4H-SiC. Of the two types of ripple structures, fine and coarse, the threshold fluence for the formation of the fine ripple was remarkably reduced on the surface roughened by intentional rubbing, while the threshold for the formation of the coarse ripple was not affected. The result suggests that the initial surface roughness plays a significant role only for the formation of fine ripples. A brief explanation will be given on the qualitative basis for the specific effect of surface morphology to the fine ripple formation.