Saturable absorber: transparent glass-ceramics based on a mixture of Co:β-ZnSiO and Co:ZnO nanocrystals.

We report on the development of novel saturable absorbers for erbium lasers based on transparent glass-ceramics (GCs) containing a mixture of cobalt-doped β-willemite, Co:β-ZnSiO, and zinc oxide, Co:ZnO, nanosized (10-14 nm) crystals. The structure of the parent glass and GCs is studied by x-ray diffraction, differential scanning calorimetry, transmission electron microscopy, and Raman spectroscopy. Variations of absorption spectra with heat-treatment reveal that Co ions from the parent glass enter the crystals of ZnO and β-willemite. GCs are characterized by a broad absorption band due to the A4(F4)→T4(F4) transition of Co ions in tetrahedral sites spanning up to ∼1.74  μm, relatively low saturation fluence, F=0.75  J/cm at 1.54 μm, short recovery time, τ=830  ns, and high laser damage threshold, ∼14  J/cm. By using the developed GCs in a diode-side-pumped Er, Yb:glass laser, 0.77 mJ/45 ns pulses are generated.