Progress in ceramic lasers

Yttrium aluminum garnet (YAG) (Y3Al5O12) single crystals doped with active species such as Nd and Yb have been used as laser media in solid-state lasers requiring high energy and excellent beam quality. This is because single crystals have extremely high thermal mechanical properties and optical qualities and because they enable high-efficiency laser oscillation. In 1995 the authors, using polycrystalline Nd:YAG, demonstrated a high-efficiency laser that was comparable to a single-crystal laser. Subsequently, single-longitudinal-mode oscillation, green and blue laser oscillation, and ultrashort-pulse laser oscillation were reported. Using the ceramic powder approach, the authors developed a composite laser element with a complicated structure that could not be produced by crystal growth techniques. This review discusses problems of conventional single-crystal growth, the fabrication and characteristics of ceramic lasers, laser oscillation properties (continuous-wave and pulse operation), light-scattering sources in ceramics, and typical applications of ceramic lasers.