Q switch and longitudinal modes of a laser oscillator with a stimulated-Brillouin-scattering mirror

A hypersound wave grating generated by stimulated-Brillouin-scattering (SBS) is applied in a laser resonator as a nonlinear mirror. This self pumped SBS mirror can be used for a passive Q switching of the laser by operating it inside a starter cavity. The Q-switch energy and pulse duration can be varied with a neutral glass filter. The e-switch mechanism is explained and the pulse energy is calculated. As a consequence of the Brillouin frequency shift such resonators show a special behavior of the longitudinal modes. The longitudinal modes and the corresponding pulse shape of such a laser are investigated experimentally as a function of the start resonator length and the position of the SBS mirror. The results are explained by a superposition of modes of the SBS resonator taking into account their phases. Finally, the spectrum of the longitudinal modes is shown to be time dependent. These investigations yield in design criteria for efficient application of SBS mirrors as a laser resonator mirror. [S1050-2947 (99)03005-X].