Third harmonic conversion efficiency from laser-dense plasma interactions

Abstract

A perturbative nonlinear procedure is used to account for the conversion efficiency of the third harmonic reflected from a dense plasma illuminated by a short laser pulse. It is found that the power ratio of the third harmonic to that of the fundamental is given by $P_3/P_0 \sim a_0^4\, {\left( \omega_0/ \omega_p \right) }^2$, where $a_0$ is the amplitude of the incident wave, and $\omega_0$ and $\omega_p$ are the optical and plasma frequency, respectively. This power ratio was found to be in agreement with particle-in-cell (PIC) simulations. Furthermore, the model presented here predicts a resonant enhancement around a density four times critical. This effect is captured as well by numerical simulations, and proved to be a distinctive feature in the radiation spectra.