Abstract

In recent years Nd;YAG lasers with output power >1 kW have been developed.^1,2 In these lasers stable multimode resonators are typically used and the output beam divergence is 30–100 times greater than the diffraction limit.¹ Unstable resonators with radially variable reflectivity mirrors are potentially the most appropriate solution to extract high-power diffraction-limited beams,³ On account of the strong pump-induced thermal lensing of Nd:YAG rods, however, the use of unstable resonators in high average power Nd:YAG lasers is not trivial. The requirements to be satisfied for a practical application can be summarized as follows: (i) low roundtrip magnification with a limited variation with pump power; (ii) mode matching to the rod cross-section with limited variation of the mode size in the rod with the pump power; (iii) low misalignment sensitivity.

© 1992 Optical Society of America