Passively Q-switched Nd:YAG ring lasers with high average output power in single-frequency operation

Applying ${\mathrm{Cr}}^{4+}$:YAG saturable absorbers, we demonstrate efficient passively $Q$-switched operation of diode-pumped Nd:YAG lasers with a maximum average output power of more than 800 mW. Pulse durations below 3 ns, energies of 70 $\mathit{\mu }\mathrm{J}$, and peak powers of 30 kW are observed with kilohertz repetition rates. Single-frequency operation is accomplished for all output powers by a nonplanar ring geometry.