Spectral Manipulation of Raman Amplifiers

Backward Raman amplifiers provide a promising path to the next generation of short pulse high-intensity lasers that can go beyond the damage limit of conventional materials. The main idea is to couple a short seed and a long counter-propagating pump through an electron plasma wave in such a way that the pump energy is transferred to the seed that is amplified and compressed via Raman backscattering. This paper will shortly review the physics of Raman amplifiers including two recent developments in the field: (a) mitigating the relativistic phase-mismatch and the resulting saturation by detuning of the pump pulse and (b) multi-frequency amplification of pulses with a beat-wave waveform.