Theory of mode locking at coherent Brillouin interaction

Locking different components of stimulated Brillouin radiation is considered in an optical resonator for a partial filling of the resonator with a Brillouin-active medium exhibiting a coherent (parametric) interaction between the components. The dependence of the type of stable locking on the form of the longitudinal filling of the resonator with the Brillouin-active medium is shown and investigated. In particular, the possibility of the formation of single (over the period
T = 2 \pi/\omega_{B}
, where ω
B
is the Brillouin shift) light pulses is shown, provided the length of the medium ranges in intervals spaced by a characteristic "Brillouin" length
L\min{B}\max{(0)} = \piC/\omega_{B}n
(where
n
is the medium refractive index). A new mechanism of mode locking in lasers is proposed and considered, owing to the coherent interaction between modes in the Brillouin-active medium (which partly fills the laser resonator), the effect being achieved, in particular, for the intensities of the modes generated less than the threshold of stimulated Brillouin radiation in the resonator. The conditions are elucidated of the formation of single (over the period
T
) light pulses.