Stimulated Raman scattering in a non-eigenmode regime

Stimulated Raman scattering(SRS)in plasma in a non-eigenmode regime is studied theoretically and numerically.Different from normal SRS with the eigen electrostatic mode excited,the non-eigenmode SRS is developed at plasma density ne>0.25nc when the laser amplitude is larger than a certain threshold.To satisfy the phase-matching conditions of frequency and wavenumber,the excited electrostatic mode has a constant frequency around half of the incident light frequency ω0/2,which is no longer the eigenmode of electron plasma wave ωpe.Both the scattered light and the electrostatic wave are trapped in plasma with their group velocities being zero.Super-hot electrons are produced by the non-eigen electrostatic wave.Our theoretical model is validated by particle-in-cell simulations.The SRS driven in this non-eigenmode regime is an important laser energy loss mechanism in the laser plasma interactions as long as the laser intensity is higher than 10^15 W/cm^2.