Nanosecond laser pulse induced concentric surface structures on SiO2 layer.

We report the periodic concentric surface structures on SiO2 layer induced by a single shot nanosecond laser pulse at 1.06 μm. The fringe period of the structures ranges from 7.0 μm to 26.8 μm, depending on the laser fluence and the distance from central defect precursor. The size and depth of the damage sites increase almost linearly with the laser fluence from 19.6 J/cm(2) to 61 J/cm(2). Plasma flash was clearly observed during the damage process. We attribute the formation mechanism of the structures to the interference between the reflected laser radiations at the air/shock-front and the shock-front/film interfaces.