Femtosecond laser-induced concentric ring damage patterns on fused silica surfaces

To investigate the radially concentric ring structures generated by single femtosecond laser pulse on the fused silica surface, we develop a coupled interference-electron-dynamics model. The model incorporates the spatiotemporal Gaussian pulse profile, a rate equation for multiphoton and avalanche ionization, and the transient refractive index perturbation derived from the Drude formulation. Through the pulse-induced phase evolution, the model reconstructs both the surface energy distribution and the spatiotemporal evolution of the electron density. The simulations produce concentric interference rings whose spacing is largest at the center and decreases with increasing radius. The single-pulse experiments reveal similar concentric rings, and their inter-ring interval changes in the same way as in the simulations. The combined simulation-experiment framework provides a practical tool for predicting the intra-pulse optical driving pattern and ring-scale metrics in single-pulse femtosecond irradiation. It may also support the design and control of femtosecond-laser microstructuring strategies.