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 $1.0\mathrm{\mu }\mathrm{m}$ pump laser, a $1.8\mathrm{\mu }\mathrm{m}$ 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.

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• Laser-plasma interactions
• Plasma optics
• Stimulated Brillouin & Raman scattering in plasmas