High-power continuous-wave Tm³⁺:Ho³⁺-codoped fiber laser operation from 2.1 µm to 2.2 µm

A Tm³⁺:Ho³⁺-codoped free-space single-oscillator fiber laser is under investigation with special focus on the power scalability of emission wavelengths from 2.1 µm to 2.2 µm. Using a tunable diffraction grating, a 200-nm tunable laser source is built. Laser output powers above 10 W are delivered from 1990 nm up to 2190 nm, demonstrating the range for stable high-power laser operation. By replacing the diffraction grating by a highly reflective, narrow linewidth volume Bragg grating, power scaling is performed at 2.1 µm and is even enabled at a wavelength of 2.2 µm. Using a volume Bragg grating (VBG) at 2.1 µm, a slope efficiency of 49% is measured with an output power of 262 W. Using another VBG with a center wavelength of 2.2 µm, the fiber laser delivers a record power of 77 W with a slope efficiency of 29%.