402 / 2019-02-28 19:01:40

Competition between the two-plasmon decay of the backscattered light and the stimulated Raman side-scattering induced by the filamentation of the scattered light

Two-plasmon decay instability, Stimulated Raman Side Scattering, Particle-in-cell instability

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The competition between the two-plasmon decay (TPD) of the backscattered light of the stimulated Raman scattering (SRS) and the stimulated Raman side-scattering (SRSS) induced by the filamentation of the forward scattered light of the SRS in the plasma with the density near one-tenth of the laser critical density is investigated with the help of two-dimensional particle-in-cell simulations. It is shown that, with an optimal laser intensity and a matched plasma density, the TPD instability of the backscattered light will be excited, but no SRSS will be excited. Then the stimulated Raman backscattering (SRBS) will be suppressed. However, when the laser intensity is high enough, the forward544tered light will reach the threshold of the filamentation instability and then obliquely propagating scattered lights will be generated. Afterwards, these obliquely propagating scattered lights will act as seeds and be re-coupled to the laser to generates obliquely propagating electron plasma waves (EPWs). In other words, SRSS will be excited. Then the TPD of the backscattered light will be suppressed. As a result, the suppression of the SRBS is also weakened. However, if the laser intensity is kept but the plasma density is no longer matched for the TPD of the SRBS, only SRSS will be excited, which implies that the SRSS should be excited even with low laser intensity, however, it is suppressed by the TPD of the SRBS.