Monoclinic Yb3+,Li+:ZnWO4 - efficient broadly emitting laser material

Yb³⁺,Li⁺ -codoped monoclinic zinc tungstate (ZnWO₄) crystals with optimized Li⁺ content providing efficient local charge compensation were grown by the Czochralski method. Heavy Li⁺ codoping makes the Yb³⁺-doped ZnWO₄ crystals less prone to cracking, improves the Yb³⁺ segregation, reduces the melting point and induces inhomogeneous spectral line broadening. The polarized absorption and stimulated-emission cross-sections of Yb³⁺ in ZnWO4 were determined. The maximum stimulated-emission cross-section σSE is 2.94×10⁻²⁰ cm² at 1055.5 nm corresponding to an emission bandwidth of 12.2 nm for light polarization E || Np. The formation of Yb³⁺ optical centers in singly Yb³⁺-doped and Yb³⁺,Li⁺ -codoped zinc monotungstate crystals is revealed by low-temperature spectroscopy. The Yb,Li:ZnWO₄ laser pumped by a commercial 976-nm Yb-fiber laser generated 2.41 W at approximately 1.06 μm with a slope efficiency of 76.4%, a laser threshold of 143 mW and linear polarization.