Pulse lengthening by intracavity stimulated Brillouin scattering in a Q-switched, phase-conjugated Nd:YAG laser oscillator.

The usual solid-state laser systems with phase-conjugating elements produce Q-switch pulses of some 10 ns pulse width, which for many applications is too short. In the following study an additive stimulated Brillouin scattering (SBS) cell is introduced in the cavity to compensate for this Q-switch behavior by nonlinearly increasing intracavity losses resulting from the direct output coupling of the Stokes wave generated in this additive cell. For direct output coupling this study takes advantage of polarizing optical elements in the laser cavity. With this arrangement an averaged pulse duration of approximately 300 ns is realized compared with the 60-ns pulse duration that is realized when working without an additional SBS cell. The experimental results are compared with numerical calculations based on modified rate equations for the active medium and a two-wave-mixing formalism for the nonlinear interaction with the SBS media.