Compression-induced fracture in silicon dioxide as a mechanism of ultra fast plasma propagation under the action of intense laser pulse

In this paper a set of models is considered to describe the mechanism of ultra fast plasma propagation in silicon dioxide waveguide under the action of intense laser pulse. In particular, the paths via which the energy is absorbed are analyzed. For the first time, the absorption in the region ahead of the primary plasma front related to the medium fracture by the shock wave with magnitude greater than 30 k b a r is taken into account on the base of recently obtained experimental data. And it is clearly shown that this effect defines the propagation of the absorption wave with a speed ~ 3 k m / s that was observed experimentally and did not get an explanation yet. It is also shown that the competition between the energy absorption behind the shock wave and momentum losses due to transverse expansion defines the oscillations in the speed of absorption wave. The spatial period of oscillations depends unequivocally on the absorption length in the fractured region as well as on the fragments size. Obtained results can provide an interpretation of the unique experimental data on high-speed fracture of optical fibers under the action of intense laser pulse.