Fully relativistic filamentation instability of strong electromagnetic radiation in unmagnetized plasmas

Accounting for fully relativistic electron quiver velocity and large-amplitude density fluctuations driven by a fully relativistic ponderomotive force, filamentation instability of an intense circularly polarized electromagnetic wave has been investigated. Thus, the nonlinearities arising from the relativistic electron mass variation and the relativistic ponderomotive force are treated exactly, so that our theory is valid for arbitrarily large values of the radiation intensity. A novel filamentation instability is shown to exist at high pump power.