High-power regime of femtosecond-laser pulse propagation in silica: Multiple-cone formation

We present a numerical study of the (2+1)-dimensional propagation dynamics of femtosecond-laser pulses in silica. In particular, considered are pulses, whose power is tens to hundreds of times higher than the threshold for self-focusing. We solve the axially symmetric, extended, nonlinear Schrodinger equation for the laser electric field, including group velocity dispersion, Kerr nonlinearity, plasma formation and defocusing, self-steepening, and space-time focusing. Our simulation results reveal that the high-power pulses are split spatially, as well as temporally, several times into multiple cones during its propagation. This new structure is formed as a result of the interplay of strong Kerr self-focusing and plasma defocusing. The number of cones and their angle with respect to the propagation axis increase with incident pulse energy. The uncertainty, which may be contained in the evaluation of plasma response and band-to-band transition rate, and the pulse disturbance by modulation instability are also analyzed. Although these influence the details of the pulse propagation, they do not affect the essence of our results: the multiple-cone formation.