Relationship between SMBS threshold and SMBS gain

The applicability of the widely used formula for the SBS threshold from [1] was analyzed. Basing on the experimental studies, numerical modeling and literature analysis, we showd that when the determination of the SBS threshold according to the criterion of 1% of the reflected power was used, one should take the numerical coefficient of 17, and not 21. It was also shown that the definition of the SBS threshold, in which the fraction of power reflected in the process of stimulated Mandelstam-Brillouin scattering is 7%, mostly agrees with the rounded value of 20.