Dependence of the threshold increment of an SBS amplifier on geometrical parameters

The influence of parameters of the active medium of an SBS amplifier on the SBS threshold is studied. It is shown that the expression for the threshold gain increment is universal and is valid in a broad range of parameters. The threshold gain increment is measured in a light guide where the spontaneous noise can be amplified within a large solid angle. Experiments on the SBS amplification of weak images in a light guide are performed. The gain ~10⁶ is obtained without considerable distortions of the image quality.