Non-resonant excitation of relativistic plasma waves using a two-wavelength TW CO/sub 2/ laser pulse

Summary form only given. Relativistic plasma waves (RPW) can accelerate electrons with gradients in excess of a few GeV/m. Theoretical studies involving RPW driven by a two-wavelength laser pulse predict that such waves are most efficiently excited when the plasma frequency /spl omega//sub p/ = /spl Delta//spl omega/, where /spl Delta//spl omega/ is the difference between the two laser frequencies. Experimentally, the amplitude of the waves driven near this resonance condition largely follows the predictions. In these experiments, either a laser pulse was used to scatter off the plasma wave at resonant densities or an injected electron beam was used to sample the plasma wave (and to accelerate electrons). In this paper a collinear Thomson scattering technique using an independent probe beam is applied to detect the RPW. In this range, very low scattering efficiencies and small frequency shifts between the probe and the scattered beam make measurements very challenging. The results reveal that, while the amount of scattered light has a peak near resonance, up to 10 times more light is scattered at plasma densities well above resonance.