Comparison of natural and forced amplification regimes in plasma-based soft-x-ray lasers seeded by high-order harmonics

The amplification of high-order harmonics (HOH) in a plasma-based amplifier is a multiscale, temporal phenomenon that couples plasma hydrodynamics, atomic processes, and HOH electromagnetic fields. We use a one-dimensional, time-dependent Maxwell-Bloch code to compare the natural amplification regime and another regime where plasma polarization is constantly forced by the HOH. In this regime, a 10-MW (i.e., 100 times higher than current seeded soft x-ray laser power), 1.5-mu J, 140-fs pulse free from the parasitic temporal structures appearing on the natural amplification regime can be obtained.