Effect of external magnetic field inhomogeneity on the nonlinear absorption of intense laser pulse in inhomogeneous warm plasma

This paper studies the propagation of an intense laser pulse and the collisional absorption in an inhomogeneous warm plasma by taking into account the external magnetic field inhomogeneity and the ponderomotive force. The calculations are carried out and compared for different magnetic field strengths and their various configurations. For this purpose, using the hydrodynamic equations, the electron density and hence the effective dielectric permittivity of the magneto-active warm plasma are derived and the nonlinear wave equation is solved through the numerical method of Runge-Kutta. The results show that increasing the strength of the external magnetic field causes an increase in the absorption coefficient and the linear magnetic field has a higher influence on the absorption coefficient with respect to the wiggler and constant magnetic fields. Moreover, when the electron temperature increases, the amplitude of the laser field and the absorption coefficient are increased and the spatial damping rate of the laser pulse takes a peak in the plasma. The results also indicate that increasing the energy of the laser pulse causes a decrease in the nonlinear absorption, and the laser energy spatial damping is significantly decreased in contrast to the growth of the amplitude of the laser field. A qualitative comparison of the results indicates that if a linear magnetic field is applied in the same direction of the laser propagation, the collisional absorption rate will be larger with respect to the other magnetic fields. Moreover, the difference in the influence of the mentioned magnetic fields on the collisional absorption increases with increasing the electron temperature and normalized cyclotron frequency and decreases with increasing laser intensity.