Stimulated Raman backscattering amplification with a low-intensity pump

Abstract

The efficiency transfer from the pump to the seed of stimulated Raman backscattering in plasma was optimized at a pump intensity below 1014 W/cm2. Two ways were employed to obtain high-quality but low-intensity pump beams. First, the pump focus was moved away from the plasma entrance to optimize guiding the uniform part of the beam in the plasma channel. The seed was amplified from 50 μJ to 1.1 mJ after 2-mm interaction, with an effective Raman transfer efficiency over 4.7%. Second, an aperture was set to make the pump focus pass through the plasma channel. An output seed energy of 1.02 mJ was obtained when the pump energy decreased to 20 mJ, showing a transfer efficiency of 5.1%. The experimental results indicate that the transfer efficiency may be mainly suppressed by plasma heating but not spontaneous Raman scattering.