Mechanism of laser $Q$ switching by intracavity stimulated scattering

An experimental investigation was made of $Q$ switching of a laser resonator by intracavity stimulated Brillouin scattering. It was found that reduction in the high initial $Q$ factor of the resonator by distortion of the transverse structure of the radiation (for example, by the use of an active element of low optical quality) resulted in effective modulation of the $Q$ factor because of wavefront reversal in the scattering. When the active medium was $YAG:Nd^{3+}$, single giant pulses of 25-30 nsec duration, peak power 0.3-0.5 MW, and repetition frequency up to 100 Hz were obtained without circulation of the scattering substance in the $Q$ switch.