Intense laser pulse amplification using Raman backscatter in plasma channels

It has been proposed that the Raman backscatter interaction in a plasma can be used to amplify ultra-intense laser pulses. To accomplish this, energy is transferred from a long drive pulse at frequency omega(pump) to an intense seed pulse at frequency omega(seed), with a Langmuir plasma wave at frequency omega(p) mediating the transfer; the frequencies are chosen to satisfy the resonant condition omega(p) = omega(pump)-omega(seed). Diffraction of the pulses limits the interaction length in a uniform plasma, and hence the energy transfer between the pulses. However in a parabolic plasma density channel it is shown, through two-dimensional particle-in-cell simulations, that such a plasma channel can be used to guide both the amplified and drive pulses over an interaction distance much greater than a diffraction length. The seed pulse is amplified by a factor of more than 200 in energy for pulses whose widths are matched to the channel size, and achieve a peak intensity of more than 6 x 10(17) W/cm(2). Unmatched pump pulses are seen to generate much smaller gain. (C) 2002 Elsevier Science B.V. All rights reserved.