PARTICLE-IN-CELL SIMULATIONS OF RAMAN LASER AMPLIFICATION IN PREFORMED PLASMAS

摘要

The recently proposed backward Raman laser amplification scheme utilizes the stimulated Raman backscattering in plasma of a long pumping laser pulse to amplify a short, frequency downshifted seed pulse. The output intensity for this scheme is limited by the development of forward Raman scattering (FRS) or modulational instabilities of the highly amplified seed. Theoretically, focused output intensities as high as 10~(25) W/cm~2 and pulse lengths of less than 100 fs could be accessible by this technique for 1 μm lasers—an improvement of 10~4-10~5 in focused intensity over current techniques. Simulations with the particle-in-cell code Zohar are presented which investigate the effects of FRS and modulational instabilities and of Langmuir wave breaking on the output intensity for Raman amplification.