Coherent Brillouin scattering in weakly ionized plasmas

A numerical study on electron, ion, and neutral density perturbation is presented in low-temperature plasma (LTP) sources driven by the frequency detuning of two laser beams. Our study is performed in the hydrodynamic regime, which is valid when the plasma lattice period is larger than the Debye and mean free path lengths, and longitudinal plasma modes can be excited. Our attention is focused on a long-timescale in which ion acoustic waves could be excited when the frequency difference between the two laser beams approaches the value predicted by the ion acoustic wave dispersion relation. The density modulation induced by the laser beams leads to the formation of a periodic quasi-neutral plasma lattice, which causes periodic refractive index perturbations. The potential of the ion-acoustic wave resonance is discussed as a diagnostic tool for the precise measurement of plasma parameters in LTP sources through coherent scattering from the periodic index refraction perturbations induced in the plasma by the optical lattice.