The effect of scattering instability induced by high intensity seed on backward Raman amplification

Abstract

Backward Raman amplification (BRA) in plasma has become one of the most promising techniques for further promoting light intensity. In this work, BRA in plasma is simulated using one-dimensional particle-in-cell code with different seed intensity, showing that higher seed intensity (in the range of 2×1011–2×1015 W/cm2) will increase energy conversion efficiency with pump pulse of fixed intensity (2×1014 W/cm2), which is pre-depleted by spontaneous Raman scattering. We find that the scattering instability of amplified seed pulse is enhanced and the plasma wave fluctuation level is promoted with seed intensity at 2×1016 W/cm2 because the local plasma density changes in the pump scattering depletion region. In the simulations, we also found that the enhanced Raman scattering and secondary Raman scattering of amplified seed pulse causes a rapid energy consumption and earlier saturation of the amplification, which significantly affects the temporal shape of the amplified seed pulse to form a double peak shape. In addition, we explore the evolution of the energy and the pulse duration of the double peaks in detail and reveal the law of pulse energy growth with different pulse durations in a Raman amplifier.