Progress in laser pulse amplification by stimulated Raman scattering in a plasma*

Amplification and compression of short laser pulses via Raman scattering in a plasma is a promising scheme for reaching ultrahigh laser powers beyond the limit of solid-state-based laser systems. We report the recent progress in the development of a plasma amplifier for a 1-5 ps seed and 1ns pump in a 3 mm plasma with the temperature and density needed for efficient compression of the pulse when the interaction length is increased (ie. Te $\sim $ 275 eV, ne $\sim $ 1 x 10$^{19}$ /cc, Kirkwood et. al, Phys. Plasmas 2007). A high-quality amplified pulse has been observed when the pump intensity is kept below 10$^{14}$ W/cm$^2$, while beam-spray onset is consistent with a few percent of the pump energy being above the filamentation threshold. A maximum output energy of 16mJ has been achieved. These results are being used to benchmark simulations and are critical for scaling up the Raman compression to large laser systems.