Spectroscopic and laser characterization of Yb,Tm:KLu(WO4)2 crystal

• Top-seeded solution growth of Yb,Tm-codoped monoclinic KLu(WO4)2 crystals.
• Maximum Yb3+ → Tm3+ energy transfer efficiency is 83.9% for 5 at.% Yb–8 at.% Tm doping.
• The fractional heat loading for Yb,Tm:KLu(WO4)2 is 0.45 ± 0.05.
• Microchip Yb,Tm:KLu(WO4)2 laser operation with a 20% slope efficiency.
• Yb,Tm:KLu(WO4)2 vibronic laser emitting at 2.081–2.093 μm.

We report on a comprehensive spectroscopic and laser characterization of monoclinic Yb,Tm:KLu(WO4)2 crystals. Stimulated-emission cross-section spectra corresponding to the 3F4 → 3H6 transition of Tm3+ ions are determined. The radiative lifetime of the 3F4 state of Tm3+ ions is 0.82 ms. The maximum Yb3+ → Tm3+ energy transfer efficiency is 83.9% for 5 at.% Yb – 8 at.% Tm doping. The fractional heat loading for Yb,Tm:KLu(WO4)2 is 0.45 ± 0.05. Using a hemispherical cavity and 5 at.% Yb – 6 at.% Tm doped crystal, a maximum CW power of 227 mW is achieved at 1.983–2.011 μm with a maximum slope efficiency η = 14%. In the microchip laser set-up, the highest slope efficiency is 20% for a 5 at.% Yb– 8 at.% Tm doped crystal with a maximum output power of 201 mW at 1.99–2.007 μm. Operation of Yb,Tm:KLu(WO4)2 as a vibronic laser emitting at 2.081–2.093 μm is also demonstrated.