Observation of amplification of light by Langmuir waves and its saturation on the electron kinetic timescale

Experiments demonstrate the ∼77× - amplification of 0.5 to 3.5-ps pulses of seed light by interaction with Langmuir waves in a low density (1.2 × - 10¹⁹ cm^-3) plasma produced by a 1-ns, 230-J, 1054-nm pump beam with 1.2 × - 10¹⁴ W/cm² intensity. The waves are strongly damped (kλ_D = 0.38, T_e = 244 eV) and grow over a ∼ 1 mm length, similar to what is experienced by scattered light when it interacts with crossing beams as it exits an ignition target. The amplification reduces when the seed intensity increases above ∼1 × - 10¹¹ W/cm², indicating that saturation of the plasma waves on the electron kinetic time scale (<0.5 ps) limits the scatter to ∼1% of the available pump energy. The observations are in agreement with 2D PIC simulations in this case.