Theoretical Investigation of Optical Guiding of Laser Beam and Second Harmonic Generation in Plasmas

Abstract

newlineThis thesis presents the theoretical investigation on the optical guiding and second harmonic generation of Hermite Gaussian laser beam in plasmas with different nonlinearities newlineand preformed plasma channel. Starting from Maxwell s equations, the formulation newlineis based on finding the numerical solution of the nonlinear wave equation for the newlineincident laser beam by using the moment theory approach under the Wentzel-Kramers- newlineBrillouin (W.K.B.) approximation. Higher-order Hermite Gaussian laser beam is used in newlinethis research. Particular emphasis is focused on the dynamical variation of the spot size newlineof the laser beam in terms of the beam width parameters in the x- and y- directions with newlinerespect to the distance of propagation. newlineIn particular, the excitation of the electron plasma wave at pump beam frequency newlineand its interaction with the incident beam is considered to be the main mechanism of the newlinesecond harmonic generation. Further, the effect of variations of the beam width parameter newlineof the Hermite Gaussian laser beam on the second harmonic yield has been analyzed in newlinedetail for different sets of laser parameters including different modes of Hermite Gaussian newlinelaser beam and plasma parameters. newlineAlso, the density ramp, as well as the preformed plasma channel have been used for newlinethe enhanced guiding of the Hermite Gaussian laser beam, and the effect of which is visualized newlineon the second harmonic yield of the laser beam. The collisional, ponderomotive, newlinerelativistic, and relativistic-ponderomotive nonlinearities have been incorporated during newlinethe analysis. The effect of the magnetic field in the presence of a preformed plasma channel newlinehas also been observed on the propagation dynamics of the Hermite Gaussian laser newlinebeam. newlineAs a main consequence of the present research, it has been investigated that the newlinehigher-order Hermite Gaussian laser beam (having mode H02) is more suitable for the newlineself-channeling as well as second harmonic generation of the beam as compared to the newlinefundamental Gaussian beam (having mode H00). Also, it is explo