Second Harmonic Generation of High Power Elliptical Laser Beam in Underdense Plasma: Relativistic Effects
In the present work, Second harmonic generation of high power elliptical laser beam in underdense plasma is investigated by taking in to account relativistic nonlinearity. Relativistic nonlinearity results in increase in mass of electrons, which start oscillating at relativistic velocities in intense laser field. Relativistic nonlinearity results in self focusing of laser beam, if initial laser power exceeds the critical power. Due to self-focusing, the laser beam develop strong intensity gradient in the transverse direction in the focal region, which in turn generates the plasma wave at the pump frequency. This plasma wave further interacts with incident laser beam and a second harmonic is generated. Effect of variation in intensity of the laser beam and plasma density on the harmonic yield is studied in detail. Harmonic yield is found to increase with increase in plasma density and with decrease in laser beam intensity.
Keywords: Second harmonic generation, underdense plasma, relativistic nonlinearity, self-focusing, plasma wave, plasma density