Yb,Tm:LiYF₄ lasers at 1.5 and 2.3 µm pumped by a Yb-fiber laser

We demonstrate the viability of pumping Yb³⁺,Tm³⁺ codoped crystals by commercial 976 nm Yb-fiber lasers for achieving low-threshold, efficient and power-scalable operation at 1.5 and 2.3 µm. A Yb,Tm:LiYF₄ laser employing this pumping scheme generated a continuous-wave output power up to 0.70 W at ∼2307nm (the ³H₄→³H₅ transition) with a slope efficiency of 26.7%, laser threshold down to 46 mW, and linear polarization (π). It also delivered 0.60 W at 1497 nm (the ³H₄→³F₄ transition) with a slope efficiency of 26.1% and a laser threshold of 78 mW. Polarization switching at 1.5 µm between π and σ states was observed and explained by gain anisotropy. Various approaches for pumping 2.3 µm Tm lasers are discussed and compared.