Filamentation of a laser beam in a collisional plasma

Abstract

In this paper we have studied the filamentation of a laser beam in a collisional plasma when the nonlinearity in the dielectric constant arises due to nonuniform heating and redistribution of electrons. For small‐scale fluctuations [r₀< (m_i/m)^1/2 λ_m, where r₀ is the beam radius, m_i is the ion mass, m is the electron mass, and λ_m is the electron mean free path], the energy balance of electrons is mainly determined by thermal conduction. The growth rate of perturbation decreases rapidly with decreasing size of perturbation. For large‐scale fluctuations, the energy balance is mainly through collisions and the growth rate decreases with the scale length of perturbation. Maximum growth rate is obtained for some optimum value of scale length. The growth rate also has a maximum for some optimum value of intensity of the main beam.