High-efficiency 1.94 μm single-oscillator monolithic thulium-doped fiber laser with more than 200 W output power

In this paper, we present the realization of a diode-pumped monolithic thulium-doped all-fiber laser operating at 1.94 μm, employing a single-oscillator architecture (SOA). Our findings demonstrate the production of 203.2 W of laser output power from an incident pump power of 353 W at 793 nm, achieving a remarkable slope efficiency of 61.2 %. The laser features a central wavelength of 1940.6 nm with an FWHM bandwidth of 2 nm at the output signal power of 203.2 W. Notably, the laser exhibited exceptional stability, with power variations of less than 0.2 % over a continuous 2-h operation at maximum output power. To our knowledge, this achievement marks the highest output power reached around 1.94 μm while maintaining such slope efficiency and power stability based on SOA. Additionally, we introduce an innovative splicing technique for large mode area (LMA) fibers, effectively enhancing the transmission of high-power emissions. This thulium-doped all-fiber laser holds significant promise for applications in both the medical and industrial sectors.