Off-Resonance Intracavity Upconversion Pumping for High-Power 2.3-μm Tm:YLF Laser

Thulium (Tm) laser operating at 2.3 μm according to the <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> →<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>H<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</inf> transition have been in the spotlight of research and development during past decade as they offer a viable alternative to Cr<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> -based laser sources. Traditionally, multi-Watt output powers at 2.3 μm from Tm-lasers are obtained under direct diode pumping at 0.8 μm using low-brightness fiber-coupled AlGaAs diode lasers at the expense of severe thermal effects and moderate efficiency [1]. Upconversion pumping schemes, Fig. 1(a) [2], which could be addressed by high-brightness bulk and fiber ~1 μm lasers (based on Nd<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>+ or Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> ions), demonstrate improved efficiencies and are of key importance for mode-locked 2.3-μm laser sources [3].