A new saturable absorber Q switch for 1.54-µm Er:glass lasers is presented. The saturable absorber is a transparent glass ceramic that contains magnesium–aluminum spinel nanocrystallites doped with tetrahedrally coordinated Co²⁺ ions. We obtained Q-switched pulses of up to 5.5 mJ in energy and 80 ns in duration at 1.54 µm. The relaxation time of ⁴ A ₂ →⁴ T ₁(⁴ F) transition bleaching was measured to be (450 ± 150) ns. Ground-state and excited-state absorption cross sections at 1.54-µm wavelength were estimated to be (3.2 ± 0.4) × 10^-19 cm² and (5.0 ± 0.6) × 10^-20 cm², respectively.

Optical properties of cobalt-doped zinc aluminosilicate transparent glass ceramics in the visible – near-infrared (IR) spectral range have been studied. It was shown that the absorption and luminescence properties of these glass ceramics are defined mainly by tetrahedrally coordinated Co2+ ions located in ZnAl2O4 gahnite nanocrystals formed in the glass ceramic matrix. The luminescence in the visible and near IR was assigned to the transitions from the T14(4P) to the A24 and T24 energy levels of tetrahedrally coordinated Co2+ ion. Absorption saturation and bleaching relaxation under excitation of the A24→4T1(4F) transition were studied. Luminescence decay and bleaching relaxation times lie in the ranges 25–200 and 500–800 ns, respectively, depending on the Co concentration. The value of the ground-state absorption cross section of tetrahedrally coordinated Co2+ ions in zinc aluminosilicate transparent glass ceramics was estimated to be 2.0×10−19 cm2 at the wavelength of 1.54 μm.

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