Abstract

Relativistic plasma waves (RPW) can accelerate electrons with gradients in excess of a few GeV/m.¹ Theoretical studies involving RPW driven by a two-wavelength laser pulse predict that such waves are most efficiently excited when the plasma frequency ω_p = Δω, where Δω is the difference between the two laser frequencies.² Experimentally, the amplitude of the waves driven near this resonance condition largely follows the predictions.^1,3-5 In these experiments, either a laser pulse was used to scatter off the plasma wave at resonant densities near 10¹⁷ cm^−33,5 or an injected electron beam was used to sample the plasma wave (and to accelerate electrons).^1,4 In this paper a collinear Thomson scattering (TS) technique using an independent probe beam is applied to detect the RPW at plasma densities 10¹³ cm⁻³÷10¹⁷ cm⁻³. In this range, very low scattering efficiencies and small frequency shifts between the probe and the scattered beam make TS 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.

© 2002 Optical Society of America