Numerical simulation study on distinguishing nonlinear propagation regimes of femtosecond pulses in fused silica

We perform numerical simulations to investigate the nonlinear propagation dynamics of femtosecond Gaussian and vortex beams in fused silica. By analyzing the extent of spectral broadening, we are able to distinguish between the linear, self-focusing, and filamentation regimes. Additionally, the maximum intensity and fluence distribution within the cross-section of the vortex beams are analyzed for different incident laser energies. The results demonstrate a direct correlation between the spectral broadening and the peak intensity of the femtosecond laser pulse. As a result, this provides a theoretical foundation for distinguishing different propagation regimes, and determining critical powers for self-focusing and filamentation of both femtosecond Gaussian and structured beams.