Self-focusing of High Power Laser Beam in Underdense Plasma and Its Effect on Second Harmonic Generation: Effect of Relativistic and Ponderomotive Nonlinearity

摘要

In the present communication, self-focusing of high power laser beam in underdense plasma and its effect on second harmonic generation is investigated by taking in to account the combined effect of relativistic and ponderomotive nonlinearity. There is redistribution of carriers on account of combined effect of relativistic and ponderomotive nonlinearity. As a result, a transverse density gradient gets established in plasma, which results in to excitation of electron plasma wave at pump wave frequency. Excited electron plasma wave in turn interacts with pump beam thereby generating second harmonic of incident laser beam. The differential equation governing the evolution of spot size of laser beam has been derived by making use of paraxial ray approximation and has been solved numerically. Effects of variation in intensity of laser beam, plasma density, plasma temperature and combined effects of relativistic and ponderomotive nonlinearites on beam width parameter of laser beam as well as second harmonic yield are also analyzed.