Statistical analysis of the parameters of stimulated Brillouin scattering under conditions of stimulated emission from spontaneous noise

A description is given of a new approach to an analysis of the statistics of fluctuations of stimulated scattering which are due to the noise nature of spontaneous radiation. The approach is based on amplification of spontaneous noise in a given excitation field under conditions of stimulated Brillouin scattering (STBS) and on a statistical analysis of noise fluctuations by two methods: in real time and after a fixed time delay when the number of realizations is large. A report is given of experiments carried out at T = 300 K in long single-mode glass fiber waveguides where a transverse distribution of optical fields could be controlled rigorously and kept constant throughout the zone of interaction between the waves. An exponential distribution of the stimulated scattering intensity was established, indicating constancy of the exponential statistics of fluctuations of the intensity of spontaneous radiation in the course of its amplification. This made it possible to calculate the STBS emission spectrum. A determination of the STBS gain increment demonstrated a good agreement between the theory and experiment. A time relationship established between the pump intensity spectrum and the emission spectrum made it possible to find the relaxation time of hypersound in a glassy medium.