The key challenge for developing high-average power solid-state lasers is thermomechanical distortions caused by waste heat deposited in the gain medium by optical pumping. If a thin laser crystal disk is used with a nearly flat-top pump profile, the heat flux can be considered to be one-dimensional. Thermal lensing and stress-induced birefringence are dramatically reduced. A nearly flat top pump profile is achieved with a good design for the four-pass optical coupling system. An average output power of 216 W is obtained from two disks with a thickness of 1 mm. The peak power of each diode array is 2000 W with 15% duty cycle. The optical-to-optical conversion efficiency of the laser system is about 36% and the electrical-to-optical conversion efficiency is more than 16%. The beam quality factor is measured to be 12×13 in a stable resonator.