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Diode-pumped laser oscillation in highly Nd3+-doped polycrystalline Y3Al5O12 (YAG) ceramics has been demonstrated. The Nd:YAG ceramics are highly transparent; the loss of a 2.3 at. % neodymium-doped ceramic is as low as that of a 0.9 at. % Nd:YAG single crystal. The high doping of Nd3+ ions realizes large pump absorption; a 6.6 at. %-doped ceramic has an absorption coefficient of 60.4 cm−1 at 808 nm. The same concentration quenching parameter is obtained between the Nd:YAG ceramics and Nd:YAG single crystals. A laser using an 847-μm-thick 3.4 at. % Nd:YAG ceramic as a gain medium operates at 2.3 times higher output power than the same laser with a 719-μm-thick 0.9 at. % Nd:YAG single-crystal gain medium.

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The thermal-birefringence effect in Nd(3+) -doped YAG ceramics has been investigated. The amount of depolarization induced by thermal birefringence in Nd:YAG ceramics is nearly the same as that in (111)-cut single crystals at the same Nd(3+) concentration. However, depolarization becomes larger as the Nd(3+) concentration increases, even at the same absorbed pump power.

Continuous-wave power of 189 mW at 473 nm with 49% conversion efficiency is generated from a 8.5 mm long uncoated periodically polled MgO:LiNbO3 ridge-type waveguide by frequency doubling of a diode end-pumped Nd:Y3Al5O12 laser at room temperature; the corresponding internal blue power and conversion efficiency were 222 mW and 58%, respectively. The highest conversion efficiency of 63% (74% with respect to the blue internal power) was obtained from a 12 mm long waveguide with 99 mW blue output power. Saturation of output blue power was observed for coupled fundamental power into the waveguides in excess of 200 mW.