Polycrystalline ceramic lasers

Polycrystalline ceramic laser rods, composed of a cubic solid solution of 89 mole% Y2O3, 10% ThO2, and 1% Nd2O3, were made by a conventional ceramic sintering approach. Rods of this material, called Nd-doped Yttralox (NDY) ceramic, have lasing thresholds between 16 and 30 J when employing a 95% output mirror reflectivity and a pump pulse of 150 μsec; the lasing slope efficiencies are approximately 0.1%. As a reference for comparison, a commercially available Nd-doped glass laser exhibits a threshold energy of 9 J and a lasing slope efficiency of 0.44% under the same testing conditions. Active attenuation coefficients for the NDY rods examined were between 5 and 7% cm−1. The lower values are within a factor of 6 of that found for laser glass. The major contribution to the attenuation coefficients for NDY laser rods, as currently produced, is a result of unidentified submicroscopic scattering centers. Direct observation of the pore size distributions in these highly transparent sintered ceramics reveals that (i) the volume fraction of pores is of the order of 1 ppm, (ii) there is a peak in the pore size distribution between 1 and 2 μm, (iii) pore growth to this size most likely occurs during the sintering process, and (iv) pores are not the major scattering centers responsible for high scattering losses.