Vertical Bridgman growth and optical characterization of LiNbO 3:Cu:Ce crystals

Abstract

In this paper we grew the LiNbO 3:Cu:Ce crystals with the size of φ 25 mm×65 mm along the Z axis by the vertical Bridgman method. The UV-visible absorption spectra and OH − absorption spectra of 2-mm thick crystal samples cut from the bottom, middle and top parts of the as-grown crystal were measured with a Shimadzu spectrophotometer. It was found that the absorption edge at the absorption coefficient of 20 cm −1 increased along the growth axis. The oxidized samples exhibited a difference in the absorbance of OH − peaks at 3480 cm −1, while the reduced samples showed almost the same absorbance. These optical inhomogeneities were explained in terms of the nonunity segregations of Cu and Ce ions in the LiNbO 3 crystal. The light-induced scattering effects of the poled crystal samples were also studied and compared using a green laser at the wavelength of 532 nm. Both oxidized and reduced X-cut samples with e-light showed stronger scattering as compared with the Z-cut samples. The reduced samples exhibited faster scattering effects than the oxidized ones. It was also found that the Z-cut sample with the light incident onto its + Z face had almost no scattering. In the case of low incident power density, the reduced samples exhibited stronger scattering than the oxidized ones at the same power density.