Transfer of pump spatial variations to Stokes phase in Raman amplifiers

Many applications of forward Raman amplifiers require that transverse spatial amplitude and phase aberrations in the pump beam not be transferred to the phase of the amplified Stokes signal. Detailed one-dimensional depleted-pump calculation are given for two mechanisms that transfer pump aberrations to the Stokes phase. The first is multilongitudinal mode pump fluctuations that vary faster than the coherence time of the Raman transition. The second is saturated dispersion combined with a detuning either due to Raman operation off of line-center or due to the dynamic Stark effect.