Evaluation of growth, thermal and spectroscopic properties of Yb^3+-doped GSGG crystals for use in ultrashort pulsed and tunable lasers

Abstract

A series of high quality Yb3+-doped gadolinium scandium gallium garnet (Yb:GSGG) single crystals with different Yb3+ ion concentration (7.5, 10, 15 and 30 at.%) has been grown by means of optical floating zone (OFZ). Crystal structure was analyzed with X-ray powder diffraction (XRPD), showing that the Yb:GSGG crystal possesses a cubic structure with space group Ia3d, and the lattice constants decrease linearly as the Yb3+ concentration increases. Effective elemental segregation coefficients and chemical composition were investigated by X-ray fluorescence (XRF), suggesting that some Yb3+ ions occupy the octahedral site when the Yb3+ ion concentration is higher than 10 at.%. The thermal properties of Yb:GSGG crystals were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficients. Thermal conductivity was then calculated, and it exhibits a tendency to decrease with increasing Yb3+ ion concentration. Spectroscopic characterization of Yb:GSGG crystals was performed at room temperature (RT), and the stimulated emission cross section was calculated using the reciprocity method (RM) and the Fuchtbauer−Ladenburg (F−L) formula, respectively. In comparison with the radiative lifetime of the 2F5/2→2F7/2 transition, the effect of radiation trapping on the fluorescence lifetime is discussed. These research results indicate that Yb:GSGG can be regarded as a promising candidate for use in an ultrashort pulsed and tunable laser.