Energy transfer between two crossed laser beams in a nonisothermal plasma

Abstract

The energy transfer between two crossed lasers (a high frequency high amplitude pump and a low frequency low amplitude probe beam) through the coupling with a difference frequency electrostatic mode/quasimode in a plasma is examined. The electrostatic mode in an unmagnetized plasma is a linearly damped acoustic mode, while in a magnetized plasma it is also taken to be a lower hybrid mode. It is driven by the ponderomotive force due to the pump and probe beams. The electron density perturbation associated with the electrostatic mode beats with the oscillatory velocities due to the lasers to produce nonlinear current densities facilitating the energy transfer from the high frequency laser to the probe beam. Efficient energy transfer occurs when the phase matching conditions are satisfied. Even when a finite mismatch between the lasers and the low frequency mode/quasimode exists, a significant energy transfer is possible. The theoretical results for the unmagnetized plasma are in compliance with the published experimental results. In a magnetized plasma lower hybrid wave appears to be a potential contender for facilitating energy exchange between lasers.