Stimulated emission in a loop stimulated Brillouin scattering laser with a variable resonator length

An investigation was made of a loop stimulated Brillouin scattering (STBS) laser whose output radiation may contain a mode propagating in the opposite direction to the exciting radiation and modes rotated relative to this direction. It was demonstrated theoretically and experimentally that, for resonator lengths corresponding to a phase shift φ≈π, the lasing threshold of the central mode was higher than the thresholds of the first rotated modes.