Transparent non-cubic laser ceramics with fine microstructure.

Transparent polycrystalline ceramics with cubic crystal structure have played important roles in a wide variety of solid-state laser applications, whereas for non-cubic structures, single crystal only has been used. For further progress in optical technologies, effective materials beyond the current limitations are necessary. Here we report a new type of non-cubic ceramic laser material that overturns conventional common sense. It is hexagonal Nd-doped fluorapatite (Nd:FAP) ceramics with an optical quality comparable to single crystal while having random crystal orientation. It is composed of ultrafine grains with a loss coefficient of 0.18 cm-1 at a lasing wavelength of 1063 nm, and its laser oscillation was demonstrated. This is the first verification of lasing in randomly oriented non-cubic ceramics. Laser oscillation in the non-cubic ceramics was realized through both advanced liquid-phase nano-powder synthesis technology and highly controlled pulsed-current sintering techniques. Our findings should open new avenues for future solid-state laser and optical applications.