Geometrical Constraints on Plasma Couplers for Raman Compression

Backward Raman compression in plasma is based on a 3-wave resonant interaction, which includes two- counter propagating laser pulses (pump and seed pulses) and an electron plasma wave (Langmuir wave). A high-density, roughly homogeneous, plasma mediates the energy transfer between the lasers by ensuring resonance with the plasma wave. However, in practice, a laser pulse entering or leaving plasma source encounters plasma at the edges of the homogeneous section that is far too tenuous to maintain resonance. When these tenuous plasma regions are extensive, such as for the wider plasma necessary for compression at higher powers, significant inverse bremsstrahlung and seed dispersion may occur. These deleterious effects may, however, be mitigated by chirping the seed and pump pulses