Abstract.  The energy transfer between two crossed laser beams, through the coupling with an ion-acoustic wave in a plasma is studied. The large amplitude laser beam couples with the density perturbation associated with the ion acoustic mode, producing a nonlinear current and amplifying the low amplitude beam. The two laser beams exerts a ponderomotive force on electrons, affecting the ion acoustic wave. Efficient energy transfer to the probe beam occurs when the phase matching conditions are satisfied. When a finite mismatch between the lasers and the low frequency mode/ quasimode exists, still a significant energy transfer is possible. The theoretical results are in compliance with the published experimental results.