Infrared spectroscopic and laser characterization of Tm in disordered double tungstates

The relative energy and characteristics of the Tm3+ levels in tetragonal double tungstate (DT) and double molybdate (DMo) crystals are investigated by low temperature optical spectroscopy with special emphasis on NaLa(WO4)2. In this host the transition bandwidths are intermediate between those found in ordered monoclinic DT and in other disordered tetragonal DT and DMo crystals. This allows for better band resolution of the S4 site symmetry features in the disordered scheelite-like structure. The potential of such Tm-doped crystals for building infrared tunable lasers is discussed on the basis of the calculated cross sections and their comparison with the experimental photoluminescence. Information on the crystal growth and Tm3+ spectroscopic details are provided. Tm:NaLa(WO4)2 laser operation with the available sample is more efficient for σ-polarized configuration. Up to 200 mW of output power was obtained at λ = 1888 nm and laser tunability extends from 1789 to 1950 nm.