Onset of laser light filamentation in preformed plasmas

The onset of laser beam filamentation in a preformed nonuniform plasma is investigated by using a two-dimensional computer code in which time-dependent plasma hydrodynamics and heat transport effects are accounted for. Laser beam propagation is modeled using a paraxial wave approximation-refraction, diffraction, absorption, and ponderomotive force effects are accounted for. The simulations reveal details by which multifilamentary plasma and laser beam structures evolve in the region near the critical density surface. For the particular case of a 1.05 μm laser beam with an intensity of 10¹⁵ W/cm² incident on a long scale length preformed plasma, a consistent treatment of the ponderomotive forces and of the plasma dynamics is found to be essential in determining the evolution of the filamentary structures.