Towards the Generation of Petawatt Near-Infrared Few-Cycle Light Pulses via Forward Raman Amplification in Plasma.

Light amplification toward extremely high power in the infrared regime remains a significant challenge due to the lack of suitable gain media. Here we propose a new scheme to amplify a laser pulse with tunable wavelengths toward extremely high power via forward Raman amplification in plasma. Different from previously proposed schemes based upon backward Raman or Brillouin amplification, our scheme involves a pump pulse and a seed pulse copropagating in moderate density plasma, with the phase matching conditions for forward Raman scattering fulfilled. Due to their group velocity difference in plasma, the pump with a shorter wavelength and longer duration will chase the seed and transfer energy to the latter efficiently. Analytical models for both linear and nonlinear stages of amplification as well as particle-in-cell simulation show that, by employing a 1.0  μm pump laser, a 1.8  μm seed pulse can be amplified 10^{4} times in its intensity and then self-compressed to nearly single-cycle. Our scheme shows the merits of high efficiency, high compactness, and relatively easy implementation with the copropagating configuration, which may provide a unique route toward the petawatt few-cycle infrared laser pulses.