Mechanism of laser induced filamentation in dielectrics.

Femtosecond laser filamentation in transparent media has a wide range of applications, from three dimensional manufacturing to biological technologies to supercontinuum generation. While there has been extensive investigations over the last two decades, there remain aspects that are not understood, owing to the complexity of the interaction. We revisit intense femtosecond laser interaction with dielectric materials at 800nm under tight focusing via high resolution three dimensional simulations, where the complete set of Maxwell's equations is solved. We simulate filament formation for a range of tight focusing conditions and laser energies, and through this are able to shed new insight on the dynamics. We find that the role of the Kerr effect is very different depending upon the degree of tight focusing. We are also able to observe the formation of two distinct damage zones for intermediate tight focusing, similar to what was seen but not fully understood almost two decades ago.