Investigation of stimulated Raman scattering in an optical waveguide by recording Stokes components opposite to the pump wave

A method for investigating the dynamics of stimulated Raman scattering (STRS) in optical waveguides is discussed. This involves recording the emission of Stokes components propagating in the opposite direction to the pump pulses. It is shown that the opposite radiation is found as a result of Rayleigh scattering of the STRS Stokes component parallel to the pump wave if the duration of the pump pulse is much shorter than its time of propagation through the waveguide and the pulse energy is insufficient for appreciable conversion of the pump radiation to the opposite Stokes components of STRS and stimulated Brillouin scattering in a time equal to the pulse duration. Under these conditions, the nonlinear distortions of the recorded signal are negligible. As an example of the use of this method, the local gains of the STRS Stokes component excited by $\lambda=0,53\mu m$ pump radiation in a quartz fiber-optical waveguide 650 m long and the attenuation factor of this component in the end section are determined.