Concentric ring structure on the front surface of fused silica induced by a focused femtosecond pulse laser

Structural changes of the transparent materials induced by a Femtosecond laser play an important role in the field of femtosecond laser micromachining. In this paper, a concentric ring structure with a period of 2 μm has been observed on the front surface when a single femtosecond pulse was focused at 15 μm below the fused silica surface with an input pulse energy of 2 mJ. A linear correlation between the size of the concentric ring structure and the input pulse energy has been revealed. A model based on the nonlinear Schrödinger equation has been used to calculate the radial light intensity distribution on the fused silica surface. The calculated light intensity distribution and the experimental results are well mapped to each other, which can be expected to provide a new perspective for the exploration of the formation mechanism of the laser-induced concentric ring structure.