Theoretical and experimental studies of a high output passively Q-switched diode-pumped cw Nd:YAG laser with Cr 4 + :YAG crystal as saturable absorber are presented. The thermal lensing effect of the saturable absorber is estimated considering the spatial and time intensity dependence of the saturable absorption on laser pulses. Treating it as a second thermal lens, the thermal and mechanical stability of a resonator with two thermal lenses is analyzed which shows that the thermal effect of the saturable absorber is an important fact in resonator design for high output lasers. As a result, an average output power of 7-12 W and pulse duration of 100-250 ns was obtained with kilohertz repetition rates. The highest peak power and pulse energy obtained were 30 kW and 3.4 mJ, respectively.