Monoclinic zinc monotungstate Yb3+,Li+:ZnWO4: Part II. Polarized spectroscopy and laser operation

Monoclinic ytterbium-lithium codoped zinc monotungstate crystal (Yb3+,Li+:ZnWO4) is a promising material for laser opertation at ~1.06 μm. Absorption, σabs, and stimulated-emission, σSE, cross-sections are determined for light polarized along the optical indicatrix axes, E || Np, Nm and Ng. At room temperature, the maximum σSE amounts to 2.81 × 10−20 cm2 at 1055.6 nm (for E || Np) and the gain bandwidth reaches ~22 nm (for E || Ng). The radiative lifetime of the upper laser level is 0.37 ms. The Stark splitting of Yb3+ multiplets is resolved with low-temperature (6 K) spectroscopy revealing a relatively large total splitting of the ground-state, ΔE(2F7/2) = 804 cm−1, being remarkably high as compared to other Yb3+-doped tungstate crystals. A notable inhomogeneous broadening of the zero-phonon line is detected at 6 K. A continuous-wave diode-pumped 1.8 at.% Yb3+,Li+:ZnWO4 laser generated a maximum output power of 2.90 W at ~1059 nm with a slope efficiency of 57.9% and a linearly polarized output (E || Np). Yb3+,Li+:ZnWO4 is attractive for broadly tunable and mode-locked oscillators.