Modulational Instability of Arbitrary Intense Lasers in the Relativistic Hot Electron-Positron Plasma

Modulational instability of lasers with arbitrary intensities, ranging from the weakly relativistic to ultra-relativistic, in a relativistic hot electron-positron plasma is studied. Using a fully relativistic fl uid model coupled with Maxwell equations, a modified nonlinear Schr & ouml;dinger equation for laser envelope evolution in plasmas is obtained. Then theoretical and numerical studies on the modulational instability of lasers are given in the regimes of low- and high- temperature limit. The results show that the growth rate of modulated instability is closely related to the ponderomotive force, relativistic and thermal effects. Moreover, due to the competition of these effects, the growth rate of modulation instability shows a non-monotonic change with the laser intensity and plasma temperature.