Growth and characterization of large Nd,Cr:GSGG crystals for high-average-power slab lasers

Abstract

Nd,Cr:GSGG crystal boules up to 13 cm in diameter and 20.5 cm long have been grown by the Czochralski method. Several problems with Nd,Cr:GSGG growth were identified, and solved separately but not all at once; these problems included spiral boule growth, 1- mu m absorption loss, iridium on the melt surface, iridium inclusions, boule cracking, dislocation, and fine scattering (smoke). In the grown crystals parameters relevant to their eventual use as gain elements for large slab lasers were measured including optical homogeneity, birefringence, absorption loss at 1 mu m, scattering loss, and iridium inclusions. The optical homogeneity of the boules is good, except for a radial gradient in refractive index of about 10/sup -5/ cm/sup -1/. The birefringence is low (<3 nm/cm) in slabs cut from the boules. Scattering losses in the boules range from 0.01 to 0.08 cm/sup -1/. This absorption has been reduced to <0.0025 cm/sup -1/ in small samples using reducing heat treatments, but appropriate treatment conditions for full-scale slabs have yet to be determined.