Laser pulse amplification upon Raman backscattering in plasma produced in dielectric capillaries

Femtosecond-pulse amplification upon stimulated Raman scattering is experimentally demonstrated for the case of a counter-propagating femtosecond laser pulse and a frequency-modulated broadband pump pulse with the same carrier frequency in a dielectric capillary filled with gas plasma. A value of ～10³ obtained for the spectral intensity amplification and ～10² for the output energy are the highest ever achieved for these quantities to date. Numerical simulation demonstrates good agreement with the experimental results. Based on the experimental data and the results of theoretical calculations, we propose a hydrodynamic mechanism for plasma-wave breaking as the mechanism playing an important role in the amplification restriction in the scheme considered.