Growth, spectroscopy and 2 μm laser operation of monoclinic Tm3+:ZnWO4 crystal

We report on the crystal growth, polarized spectroscopy, and laser operation of monoclinic Tm 3+ , Na + (Li + ) codoped zinc monotungstate (ZnWO 4 ) crystals. The Li + codoping with an optimized Tm/Li ratio enables almost complete local charge compensation leading to better crystal quality, higher Tm segregation coefficient, and longer luminescence lifetime and ultimately the demonstration of laser operation. The modified Judd-Ofelt theory was employed to calculate the Tm 3+ transition probabilities yielding a radiative lifetime of the 3 F 4 state of 2.59 ms. The corresponding intensity parameters are Ω 2 = 5.194, Ω 4 = 0.658, Ω 6 = 0.471 [10 −20 cm 2 ] and α = 0.110 [10 −4 cm]. Tm,Li:ZnWO 4 features strongly polarized emission spectra extending beyond 2 μm owing to a large total Stark splitting of the ground-state, Δ E ( 3 H 6 ) = 644 cm −1 . The stimulated-emission cross-section in this spectral range reaches 0.47 × 10 −20 cm 2 at 2015 nm for light polarization E || N p . The continuous-wave Tm,Li:ZnWO 4 laser generated 282 mW at 1.98 μm with a slope efficiency of 14.7 %, and laser emission at 2.03 μm was also achieved. • Czochralski growth of monoclinic Tm 3+ , Na + (Li + ) codoped zinc monotungstate (ZnWO 4 ). • Li + codoping provides higher Tm 3+ segregation and longer luminescence lifetime. • Tm,Li:ZnWO 4 features strongly polarized emission spectra extending beyond 2 μm. • The stimulated-emission cross-section is 0.47 × 10 −20 cm 2 at 2015 nm. • First continuous-wave laser operation of Tm,Li:ZnWO 4 crystal at 2 μm is demonstrated.