Effect of plasma channel non-uniformity on resonant third harmonic generation

Abstract

We study the generation of resonant third harmonic laser radiation in a density non-uniform rippled plasma channel. An introduction of plasma channel non-uniformity strongly enhances the self-focusing and compression of main laser pulse at lower powers. In a deeper plasma channel, self-focusing is less sensitive to laser amplitude variation but increases compression. Plasma density ripple 'n(q)' leading to resonant third harmonic generation when k(q) = 4 omega(2)(p)/3m(e)omega(0)c gamma(0), where 'omega'(p) is electron plasma frequency, 'omega(0)' is laser frequency, and 'gamma(0)' is the electron Lorentz factor. Third harmonic is produced through the beating of ponderomotive force induced second harmonic density oscillations and the oscillatory velocity of electrons at main laser frequency. The self-focusing and compression of the fundamental pulse periodically enhances the intensity of the third-harmonic pulse at lower powers of main laser. In a deeper plasma channel, the third harmonic power is less effective by self-focusing and the compression of main laser, and increase with main laser pulse power.