摘要： Cobalt ions (Co2+) embedded in tetrahedral (Td) sites are known for their intense absorption around 1.5 μm. Crystals such as spinel, MgAl2O4, doped with Co2+ ions in Td sites are recognized as excellent saturable absorbers (SAs) for eye-safe erbium lasers. Due to the relative difficulty to grow high-quality Co:MgAl2O4 crystals and fixed position of the Co2+ absorption band in spinel single-crystals, other Co2+-doped materials were proposed such as transparent glass-ceramics (GCs) and ceramics based on various spinels [1]. Transparent GCs offer a size-scalable synthesis method based on glass melting technology and variable spectroscopic properties as compared to crystals, and much higher laser induced damage threshold (LIDT) as compared to ceramics. GCs based on MgAl2O4 spinel nanocrystals modified by the addition of Ga3+ cations allow one to extend the SA properties until 1.7 μm [2]. In the present work, we describe the synthesis, structure, optical spectroscopy, nonlinear properties and passive Q-switching (PQS) performance of novel transparent GCs based on Co2+:Li(Al,Ga)5O8 nanocrystals. A lithium gallium aluminosilicate glass nucleated by TiO2 was doped with 0.1 mol% CoO. The GCs were produced by secondary heat-treatments at 680-850 oC for 6 h resulting in highly transparent, blue-colored samples, Fig. 1(a). The precipitation of nanosized spinel crystals was confirmed by XRD and TEM, Fig. 1(b,c), and Raman spectroscopy. The transparent GCs exhibited a broadband absorption band at 1.3-1.65 μm due to the 4A2(4F) → 4T1(4F) transition of Co2+ ions in Td sites in Li(Al,Ga)5O8 nanocrystals, Fig. 2(a). The saturable absoption of GC heat-treated at 750 oC for 6 h was studied by Z-scan method at 1540 nm using ns pulses. The saturation fluence FS is 0.50±0.05 J/cm2 and the LIDT exceeded 20 J/cm2, Fig. 2(b). This transparent GC was used to fabricate a SA for PQS of a compact diode-pumped Er,Yb:glass laser. This laser generated stable 7.4 ns / 1.34 mJ pulses at 1535 nm (peak power: 181 kW). The developed GC are promising as SAs for erbium lasers based on glass and crystalline materials (e.g., Er:YAG lasers emitting at 1617 nm and 1645 nm). This is because the broadband absorption of Co2+ ions in GCs is notably red-shifted as compared to Co:MgAl2O4 crystals which, in turn, is caused by the different spinel nanophase composition.