Nonlinear propagation of ultrafast elliptical non-diffractive beams in bulk fused silica glass

We describe the nonlinear evolution of ultrafast circular and elliptical non-diffractive light pulses designed by asymmetric spatial Fourier filtering of zeroth-order Bessel–Gauss beams in fused silica glass, in a parameter range close to plasma generation for laser material processing. We numerically demonstrate a genuine resilience of the core shape, a consequence of a self-regulated action of the Kerr nonlinearity and of the carrier plasma for preserving and even reinforcing beam ellipticity. Overcoming symmetrization trends, the asymmetric core remains constantly elliptical along its propagation for a range of input fluence close to the threshold of permanent damage. These findings, showing the emergence of a beam with a section stable against nonlinear distortions, aim to assist current ultrafast laser dicing strategies.