Multi-watt monolithic Er3+/Dy3+-co-doped fluoride fiber laser at 3425 nm for resonant processing of high-density polyethylene.

We report what we believe to be the highest power emitted by an erbium-dysprosium (Er3+/Dy3+) co-doped fiber laser and the first monolithic (all-fiber) design of such a co-doped system, taking advantage of two fiber Bragg gratings directly inscribed in the gain fiber. This laser emits up to 4.42 W of continuous power at 3425 nm, a wavelength very far from the gain peak of dysprosium, with a slope efficiency of 10%, according to the launched pump power. This represents a tenfold increase compared to the previously reported output power in this wavelength range from such a co-doped fiber laser. The laser is cladding-pumped by a standard 976 nm laser diode, which is a great advantage for power scaling, stability, and industrialization compared to dual-wavelength pumped erbium-doped or singly dysprosium-doped fiber lasers, which both use more complex core-pumping schemes. The emission wavelength was chosen to coincide with the absorption peak of high-density polyethylene, a common industrial polymer notoriously refractory to laser machining, opening new avenues for resonant polymer processing.