Improved resonator design for rod lasers and slab lasers

The properties of several resonator schemes, which provide high output power and good beam quality simultaneously were investigated both theoretically and experimentally. Experiments were performed with high power Nd:YAG rod systems and Nd:YAG slab systems. Best performance was achieved with unstable resonator schemes. Output power up to 230 Watts was obtained with 6 x 3/8 inch rod and unstable resonators with different reflectivity profiles of the output coupler. Destruction of the high-reflecting spot can be prevented by appropriate resonator design: the thermal lens must be exactly corrected for and a slight misalignment of the rod is necessary. The unstable resonator provides good focusability over the whole range of output power. Compared with optimized stable resonators, the output power was 25 % lower. Considerable improvement of beam quality of slab lasers was achieved by using folded stable resonators, plane- unstable resonators, on-axis unstable resonators and off-axis-unstable resonators. Common stable resonators operating near the limit of stability are too sensitive against the negative refractive power that occurs in the y-direction. Beam parameter products of 1 mm mrad and lower were measured with off-axis unstable resonators.