Influence of density ripple on pulse slippage of third harmonic generation in plasma

Influence of density ripple on pulse slippage of third harmonic generation has been investigated. When highly intense short range laser pulse incident on plasma, it imparts oscillatory velocity to electrons and exert a ponderomotive force at twice the frequency of incident laser beam. It induces oscillatory velocity at second harmonic frequency 2ω which further couples with density ripple resulting in density oscillations at 2ω. Density oscillations at 2ω, couple with the oscillatory velocity at ω, to produce non-linear current density at 3ω which drives the third harmonic generation. In order to provide phase matching condition between fundamental and third harmonic pulses, density ripple in plasma is introduced which offers the required momentum to the third harmonic photon to make the process resonant. At resonance, amplitude of the third harmonic pulse is found to be maximum for optimized values of density ripple factor. It is observed that the peak value of third harmonic pulse shifted towards higher value of normalized distance z' for higher values of normalized time t'. It is also seen that on account of the group velocity mismatch between pump and third harmonic pulses, the third harmonic pulse slips out of the domain of pump pulse.