| Ultrashort laser pulse amplification by a counterpropagating pumping beam, through Raman backscattering in plasma, has been demonstrated. The amplification and spectral characteristics of the amplified pulse agree with the linear theory of Raman amplification. This research is part of an investigation towards a new method of ultrapowerful laser pulse amplification through nonlinear stimulated Raman backscattering. Plasma density and ionization diagnostics have been developed, using the effects of non-stationary plasma on laser frequencies. These effects were demonstrated in a semiconductor by rapidly creating free-carriers in the crystal during the propagation of a laser pulse through it. This method can be used as diagnostics for Raman amplification demonstration in semiconductor plasma. Guiding of ultrahigh-intensity laser pulses in discharge-created plasma channels in LiF microcapillaries has been investigated. Transmission was measured as a function of input intensity and focusing geometry. A peak in transmission was observed at the theoretically calculated matching beam radius, at which the beam propagates at a constant radius with minimum absorption. This method has been shown not to be suitable yet for soft x-ray lasing in the recombination scheme, but can be utilized for increasing the infraction length in Raman amplification. A multi-terawatt laser system was built and its large vacuum compressor was designed and built in our lab. It is the main experimental tool in the research presented here. |
