The behaviour of passively Q-switched solid-state lasers containing intracavity optical parametric oscillators(OPOs) is described in detail. A diode-pumped passively Q-switched Nd:YAG, Cr4+: YAG laser was employed to generate a high-repetition-rate, high-peak-power eye-safe laser beam with an intracavity optical parametric oscillator (OPO) by use of a KTiOPO4 (KTP) crystal. Different ranges of repetition rates and pulse widths are obtained by using absorbers of different optical densities. With a Cr4+:YAG wafer of T0=80% low-intensity transmission, 3.8 W average power at 1.572 μm wavelength and repetition rate up to 80 kHz with pulse width as narrow as 30 ns are obtained. The peak power is up to 1.58 kW.