Precisely tapered fluorotellurite fiber-enabled Raman soliton relay fission for generating a 4–5  <b>μ</b>m mid-infrared high-power laser

Ultra-broadband supercontinuum (SC) lasers covering the mid-infrared (MIR) region have significant applications in trace substance detection, national defense, and biomedical fields. Currently, high-power SC spanning 2–5 μm is still dominated by traditional fluoride ( InF 3 ) fibers. Although tellurite fibers, with their excellent chemical and thermal stability, have demonstrated significantly higher power scalability compared to other MIR fibers, their spectral broadening capabilities in the 4–5 μm region remain largely unexplored. Here, we demonstrate a &gt;10 W ultra-broadband flat SC spanning the 1.8–5.1 μm spectral range in a fluorotellurite fiber using a cascaded soliton self-frequency shifting technique. The fluorotellurite fiber is precisely tapered to reconstruct dispersion and nonlinearity, which facilitates the evolution of the pre-stage Raman soliton into higher-order solitons, thereby enabling a new round of “rapid relay fission.” At a low pump power of 7.5 W, we also achieved a high-power (0.5 W) Raman soliton (60 fs) at 4.3 μm. These results, for the first time, to our knowledge, demonstrate that tapered fluorotellurite fibers can be used for high-power femtosecond pulse generation beyond 4 μm and high-power SC generation beyond 5 μm, establishing them as an exceptional nonlinear medium for the development of high-power MIR fiber lasers in the 4–5 μm spectral region.