Ionization-Induced Small-Scaled Plasma Structures in Tightly Focused Ultrashort Laser Pulses

The laser-matter interaction via optical-field ionization of a medium in a tightly focused ultrashort laser pulse is investigated by finite-difference-time-domain modeling of Maxwell's equations. We show that, unlike in the case of the conventional quasioptical approach, the regime of interaction changes drastically above a certain critical angle of laser beam focusing, resulting in the generation of small-scaled plasma structures which strongly influence the local field distribution and scattering characteristics.