Collisions effect in the heating of underdense plasma by a high-intensity short laser pulse

Abstract

Nonlinear heating of collisional plasma when the temporal extent of the laser pulse is smaller than the ambipolar diffusion time has been investigated. The nonlinearity in a collisionless plasma arises through the ponderomotive force, whereas in collisional plasmas ohmic nonlinearity prevails. In this case, by considering the nonrelativistic ponderomotive force effect and the variation of the collision frequency between electrons and ions due to the temperature change, the nonlinear dielectric permittivity of the plasma medium is obtained and the equation of the electromagnetic wave propagation in underdense plasma is solved. It is shown that in this case, due to the ohmic heating of electrons, the effect of the ponderomotive force in the nonrelativistic regime leads to steepening of the electron density profile and decreases the temperature of the plasma electrons noticeably. Bunches of electrons in plasma become narrower and by increasing the laser pulse strength the wavelength of density oscillations decreases. In this regime of laser–plasma interaction, the electron temperature decreases sharply with increasing the intensity of laser pulses.