Generating the Optimum Self-Focusing in the Relativistic Laser-Plasma Interaction

In this paper, the effect of basic parameters of laser and plasma on controlling self-focusing is investigated, and based on the introduced effective parameter for self-focusing (EPSF), the effects of laser wavelength, the initial spot size of laser beam, the initial intensity of laser, and the plasma electron density on self-focusing are discussed. It is found that the relativistic self-focusing strongly depend on the laser wavelength and the beam intensity. The nonlinear effect of beam intensity on the introduced parameter EPSF indicates that after an increasing region for focusing, the self-focusing effect decreases at ultrarelativistic intensities. The effect of the initial beam spot size on the introduced parameter EPSF indicates that pulses with larger spot sizes can be focused stronger, and the diagram of EPSF versus the electron density shows the direct dependence between self-focusing and the initial plasma density. The nonlinear effect of laser wavelength on self-focusing also is studied at relativistic and ultrarelativistic intensities. The presented model introduces the optimum selection of laser and plasma parameters for achieving the desired focused/unfocused laser beam in the relativistic laser-plasma interaction.