Localization of a Gaussian laser beam in thermal quantum plasma with density ramp

This work investigates the localization of a Gaussian laser beam in thermal quantum plasma with a density ramp. Assuming the Wentzel-Kramers-Brillouin, and paraxial approximations, the mathematical formulations for the laser beam width parameter in the thermal quantum plasma are achieved and solved numerically by the fourth-order Runge-Kutta method. Results show that the laser beam radius is an essential factor in determining the behavior of the laser beam in plasma. Also, considering plasma with a density ramp, a laser beam with oscillatory divergence could be localized in a steady self-focusing region. Then a parameter as critical normalized beam radius is defined so that if the laser radius is higher than this value, the beam experiences stable convergence in the plasma. Furthermore, the effect of laser intensity on critical normalized beam radius for different Fermi temperatures is studied. It is seen that after a value of intensity, the critical normalized beam radius becomes almost independent of laser intensity. In addition, the variation of laser intensity with propagation and radial distances for diverse values of the initial beam radius is investigated. It is found that when the laser beam oscillates in a steady self-focusing region, the number of intensity fluctuations, as well as the maximum laser intensity in the focal points, are significantly different compared to the other two areas. Increasing the laser intensity in focal regions enhances the laser absorption and conversion efficiency, thereby improving the laser-plasma interaction. These results could help improve laser-plasma interaction where the quantum effects are dominant.