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Self-Focusing of Laser Beams in the Paraxial Ray Approximation in Collisional Inhomogeneous Plasmas for Arbitrary Large Magnitude of Nonlinearity

Ghanshyam, Rajeev K. Verma, Narayan Kumar, Sudesh K. Jayaswal and Bhrigunandan Prasad Singh

This paper presents an investigation of the self-focusing behaviour of radially symmetrical Gaussian laser beam propagating in an axially inhomogeneous collisional plasma. Considering the nonlinearity to arise from the redistribution of electrons, due to thermal conduction across the cross-section of the beam and following the extended version of Sodha et al. theory based on the WKB and paraxial – ray approximation, the self-focusing behaviour has been investigated in some detail. The effect of different types of axial inhomogeneities in plasma, on the self-focusing of laser beam has been studied for arbitrary large magnitude of nonlinearity. The self-focusing is found to depend on type of axial inhomogeneity as well as characteristic scale length of axial inhomogeneity. When thermal conduction is the dominant mechanism of nonlinearity of dielectric constant, the critical power Pcr of the beam is seen to be the same as that given by the small nonlinearity theory. When power of the beam P > Pcr, the medium behaves as an oscillatory wave-guide.