Red-diode-clad-pumped Er³⁺/Dy³⁺ codoped ZrF₄ fiber: A promising mid-infrared laser platform

We report, for the first time, to the best of our knowledge, mid-infrared (mid-IR) laser generation, from a red-diode-clad-pumped Er³⁺/Dy³⁺ codoped ZrF₄ fiber laser. A free-running laser at ∼3.4 µm, mainly from the ⁴F_9/2→⁴I_9/2 transition of Er³⁺, directly excited by a 659-nm laser diodehas been achieved at room temperature with a maximum power of 0.8 W and 8.8% slope efficiency. In this system, the long-lived ⁴I_11/2 and ⁴I_13/2 states are rapidly depopulated by energy transfer to the codoped Dy³⁺ ions and energy transfer upconversion between the Er³⁺ ions, resulting in the accelerated recycling of ions. Additionally, the free-running dual-wavelength operation state at ∼3.3 and ∼3.5 µm is also observed, producing a total maximum power of 0.95 W with 10.7% slope efficiency, representing the first watt-class output from a diode-pumped rare-earth-doped fiber laser far beyond 3 µm. By employing a diffraction grating, continuous spectral tuning across the 642-nm range from 3053.9 to 3695.9 nm has been demonstrated. The proposed scheme provides, to the best of our knowledge, a promising new platform for laser generation in the mid-IR region of 3-4 µm.