Feasibility investigation of Ho:Nd codoped InF3 fibers pumped at 808 nm wavelength

Fiber lasers emitting in the 3-5 μm wavelength range have attracted much interest during the last years, thanks to their wide potential employment in different fields, such as remote sensing, air pollution detection, communication applications, and medical diagnostics. Fluoroindate fibers allow transmission in this range and can be doped with different rare-earth ions, including erbium, holmium, dysprosium, and neodymium. Recent experiments have shown the feasibility of emission at λ = 3.92 μm wavelength employing Ho:Nd co-doped fluoroindate glass, encouraging the investigation on continuous-wave (CW) emission lasers. In this work, a complete model of Ho:Nd co-doped fluoroindate fiber pumped at λp = 808 nm and emitting at λ = 3920 nm is developed, in order to find the unknown energy transfer parameters, thus allowing a correct design. The energy transfer parameter recovering is performed by simulating the fluoroindate fiber via a finite element method (FEM) code, by solving the rate equations with a homemade code and by matching simulations with experimental values reported in literature. The results pave the way for the accurate design of a CW laser emitting at λ = 3920 nm, potentially with better efficiency than lasers based on Ho3+-heavily-doped fluoroindate fibers. Preliminary fiber laser design has been based on commercially available fluoroindate fibers, including double cladding fibers, in order to choose the best geometry for the fiber laser and investigate its feasibility.