Abstract
The present work has been carried out to produce Cr-doped forsterite (Cr:Mg_2SiO_4) crystals with a high optical gain for a laser amplifier. In order to incorporate Cr^<4+> ions into the crystals as much as possible, the initial Cr content of the melt was increased and the O_2 gas partial pressure of 0.03atm was employed in the growth atmosphere, instead of 0.01atm in the literature. Under such conditions, Cr:Mg_2 SiO_4 crystals with a diameter of 35mm and lengths up to 185mm were successfully grown by the Czochralski method. Subsequently, crystal pieces cut out from the grown crystals were heat-treated at 1780℃ under the O_2 gas pressure of 1atm. As the result of these processes, the Cr^<4+> ion content of the crystal remarkably increased, and the crystal exhibited the optical gain which is two times as large as that of the standard crystal with almost the same as the Cr content of a commercially available one, giving promise of a laser amplifier material. Furthermore, optical microscopic observations, XRD measurements, and EPMA analyses on as-grown crystals showed that the solubility limit of Cr in the Mg_2SiO_4 crystal is only about 0.08wt.%, and that over the solubility limit, inclusions such as MgO and MgCr_2O_4 oxides are incorporated into the crystals, bringing about the occurrence of ill-shaped crystals during the crystal pulling.
