Ytterbium-doped materials are very attractive for laser-diode- (LD-) pumped solid-state lasers. The Yb-doped materials have high quantum efficiency, no concentration quenching, and long lifetime. The broad absorption band in the near-IR region is suitable for pumping with a LD, and the broad emission band is able to generate tunable laser oscillations and ultrashort pulses. So far, many Yb-doped laser materials have been researched and are used for high power lasers and ultrafarst lasers.

Since 1998, it has been possible to fabricate highly transparent ceramics for solid-state lasers by a vacuum sintering technique and nanocrystalline technology. Our fabrication method is fundamentally different from any press methods, for example the cold isotropic press method and hot isotropic press methods, because no pressure is applied through the whole fabrication process. As a result, our ceramics have good homogeneity in terms of grain size and less internal strain. Additionally, this method is suitable for the fabrication of large sized products and production in large numbers.

We have been developing highly transparent Yb-doped Y₃Al₅O₁₂ and RE₂O₃ (RE = Y, Sc, and Lu) ceramics for solid-state lasers. From spectroscopic point of view, there is no difference between an Yb:Y₃Al₅O₁₂ single crystal and the ceramics. For a RE₂O₃, the ceramics also has same spectroscopic properties as the single crystals.

The LD-pumped Yb:Y₃Al₅O₁₂ and Yb:RE₂O₃ ceramic lasers have been demonstrated. For an Yb:Y₃Al₅O₁₂, a 940-nm LD was used for the excitation. In the cw Yb:RE₂O₃ lasers, they were pumped at the zero-phonon line (ZPL) of around 976-nm wavelength. ZPL pumping has a few advantages: larger absorption cross section, lower quantum defect. In a ZPL-pumped cw Yb:Y₂O₃ laser, the extraction efficiency of 72 % was obtained at 1078 nm. An LD-pumped cw mode-locked ceramic laser oscillation was carried out. The pulse duration of 430 fs was obtained.

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1. Highly transparent YAG ceramics