Control of Nd and Cr concentrations in Nd,Cr:Gd3Ga5O12 single crystals grown by Czochralski method

During the growth process of the Nd,Cr:Gd3Ga5O12 (Nd,Cr:GGG) laser crystals the optimum concentrations of the dopants cannot be realized in axial direction of the crystal at a constant pulling (growth) rate as the effective segregation coefficients (k) of Nd3+ and Cr3+ are not unity and not uniform (k < 1 and k > 1, respectively). To solve this problem the dopant concentrations were measured in the crystals grown at different pulling rates by atomic absorption to determine the effective and equilibrium segregation coefficients and the ratio of the boundary layer thickness and diffusion coefficients. In the light of these parameters we suggest a pulling (growth) rate program as a function of the fraction of the crystallized melt leading to the smallest concentration variation of the dopants along the length axis of the crystals. The variation of Nd3+ concentration in the crystal reduced from 35% to 19% while the laser efficiency increased by 15-20% by this method. (C) 2001 Elsevier Science B.V. All rights reserved.