Observation of resonant energy transfer between identical-frequency laser beams

Enhanced transmission of a low intensity laser beam is observed when crosse d with an identical-frequency beam in a plasma with a flow velocity near th e ion sound speed. The time history of the enhancement and the dependence o n the flow velocity strongly suggest that this is due to energy transfer be tween the beams via a resonant ion wave with zero frequency in the laborato ry frame. The maximum energy transfer has been observed when the beams cros s in a region with Mach 1 flow. The addition of frequency modulation on the crossing beams is seen to reduce the energy transfer by a factor of 2. Imp lications for indirect-drive fusion schemes are discussed. [S1070-664X(99)9 4205-2].