Regime for a self-ionizing Raman laser amplifier

This is the authors' abstract. We don't add key points for this paper.

Backward Raman amplification and compression at high power might occur if a long pumping laser pulse is passed through a plasma to interact resonantly with a counter-propagating short seed pulse [V. M. Malkin et al., Phys. Rev. Lett. 82, 4448–4451 (1999)]. One critical issue, however, is that the pump may be unacceptably depleted due to spontaneous Raman backscatter from intrinsic fluctuations in the amplifying plasma medium prior to its useful interaction with the seed. Premature backscatter may be avoided, however, by employing a gaseous medium with pump intensities too low to ionize the medium and using the intense seed to produce the plasma by rapid photoionization as it is being amplified [V. M. Malkin et al., Phys. Plasmas 8, 4698–4699 (2001)]. In addition to allowing that only rather low power pumps be used, photoionization introduces a damping of the short pulse which must be overcome by the Raman growth rate for net amplification to occur. The parameter space of gas densities, laser wavelengths, and laser intensities is surveyed to identify favorable regimes for this effect. Output laser intensities of 2×1017 W/cm2 for 0.5 μm radiation are found to be feasible for such a scheme using a pump of 1×1013 W/cm2 and an initial seed of 5×1014 W/cm2 over an amplification length of 5.6 cm in hydrogen gas.