Effect of Nanocrystal Structures on Interface of Cr-Doped Yttrium Aluminum Garnet Double-Clad Crystal Fiber

摘要

In this study, we investigated both the microstructure and the chemistry of the core/inner cladding interface in Cr-doped yttrium aluminum garnet (CrYAG) double-clad crystal fiber by high-resolution transmission electron microscopy. In the axial direction, two contrasting layers were found between the SiO_2 inner cladding and the YAG crystal core (with or without heat treatment). Cr~(3+):γ-Al_2O_3 nanocrystals were observed; these nanodomains were slightly tilted at an angle of about 2° from the core YAG structures at the original interface. Subsequently, amorphous oxide layers were formed during codrawing laser-heated pedestal growth. The Cr~(3+):γ-Al_2O_3 nanocrystals had different lattice parameters and showed various structures during growth. The defect density of the core YAG near the interface was reduced after appropriate heat treatment. These results indicated that the growth kinetics can critically affect the interface chemistry in this crystal fiber. The relative fluorescence spectrum of Cr~(4+) in both low- and high-field sites was significantly affected by the nanocrystal distribution.