Tm-doped fiber laser resonantly diode-cladding-pumped at 1620 nm

We report the first demonstration of an efficient, high power, resonantly (in-band) diode-cladding-pumped Tm-doped fiber laser operating on the ³F₄  ⇒  ³H₆ transition of Tm³⁺ ion. The laser, pumped by a fiber coupled laser diode module at ∼1620 nm, delivered ∼15 W of power at 1930 nm with a slope efficiency of 67% versus the absorbed pump power. This presents, to the best of our knowledge, the highest slope efficiency and the highest output power reported so far for resonantly diode-cladding-pumped 2 µ m fiber lasers based on double-clad Tm-doped silica fibers. These very preliminary results, obtained with commercial double-clad Tm-doped fibers, unoptimized for in-band pumping at the peak of resonant absorption, indicate a very high potential of resonantly diode-cladding-pumped Tm fiber lasers for major power scaling unaffected by photodarkening. Fiber optimization for resonant pumping at the maximum of the Tm^3+   3H₆  ⇒  ³F₄ absorption band in silica (1610–1710 nm) can lead to a new generation of Tm fiber lasers with power and wall-plug efficiency, competing with those of high power tandem-pumped Tm-doped fiber lasers, but potentially with a lighter weight and smaller dimensions. (letter)