Increased Stokes pulse energy variation from amplified classical noise in a fiber Raman generator

We present an experimental and theoretical study of the transition from linear to nonlinear amplification of classical pump noise in a fiber Raman generator. In particular, we focus on the conversion of fluctuations in the fine temporal structure of Q-switched pump pulses into Stokes pulse energy fluctuations. We show that there is a distinct pump power domain where large scale fluctuations in the Stokes pulse energy result from the amplification of fluctuations in the temporal structure of pump pulses with stable energies. Dramatic changes in the shape of the Stokes pulse energy probability distribution also occur as the pump power is swept through the domain of large scale energy fluctuations.