Electric field effect on the relaxation of a plasma grating induced by two femtosecond lasers in air

Abstract

We propose a mathematical model to study the effect of an external electric field on the relaxation of a Traveling Plasma Grating (TPG) that is induced by the filamentation of two femtosecond laser beams in air plasma. The main purpose of this study is to examine the role of the applied electric field on the relaxation-delay of the formed plasma grating (PG) and to investigate the consequences of this delay on the efficiency of the energy exchange between these beams. The proposed model employs two coupled 2D envelope-equations in conjunction with a kinetic electron balance and an electron energy conservation equation to study the relaxation of the induced PG in the molecular air structure. The employed equations have been numerically solved and the simulation results have revealed that the presence of the electric field widely prolongs the electron density decay period and largely extends the electron temperature relaxation time of the induced PG at different molecular structures, furthermore it increases the energy exchange ratio between the two fs beams on these air structures.