Ultra-short laser-produced optical microcavities and ionization fronts

A class of nonlinear optical effects related to fast field ionization in an interference pattern is investigated by numerical simulations. Interferenc e between counter-propagating ultrashort pulses slightly below the ionizati on threshold produces a layered distribution of free-electron density. In a dense dielectric target, this effect allows us to trap light between plasm a layers creating a sort of optical microcavity. Other peculiar features in clude frequency upshift, pulse lengthening and self-generated relativistic ionization fronts.