The passive $Q$-switching regime in a solid state laser with a multiloop cavity

A compact, pulsed-periodic YAG : Nd$^{3+}$ laser with self-pumped phase-conjugate multiloop cavity and passive $Q$-switching by YAG : Cr$^{4+}$ and GSGG : Cr$^{4+}$ crystals has been studied. It is established that the energy and temporal parameters of radiation in separate pulses of a periodic train can be controlled almost without changing the pulse train energy. A regime of generating modulated radiation pulses with a peak power of up to 30 MW and a spatial brightness of 1.7 $\times$ 10$^{15}$ W/(cm$^{2}$ sr) at a radiation beam quality parameter of $M^2<$ 1.2 has been realized in experiment.