Efficient and compact Yb:YAG ring laser

An efficient and compact Yb:YAG ring laser was demonstrated with a slope efficiency of 39.0% with respect to the absorbed power. The design issues for using Yb:YAG as the gain medium in the reentrant multipass ring laser are discussed. The high absorption coefficient and low quantum defect of Yb:YAG make it an ideal gain medium for the multipass ring cavity to fulfil reentrant condition and reduce reabsorption loss. The absorption characteristics of a 20-at.% doped Yb:YAG crystal and the optimum ratio of absorption depth to Yb:YAG thickness were measured. The degrees of linear polarization were 99.0% and 94.1% in planar N=2 and nonplanar (N,M)=(2,1) ring lasers, respectively. The multipass ring cavities can be applied in a compact mode-locked laser with long round-trip length.