Design of a Mid-IR Laser Based on a Ho:Nd-codoped Fluoroindate Fiber

In this work, a novel mid-infrared continuous wave laser, based on a fluoroindate fiber co-doped with holmium and neodymium, is designed to emit at lambda s = 3.92 mu m, when pumped at lambda(p) = 808 nm. The laseris modeled considering a nine-level sys-tem, by taking into account experimental spectroscopical parame-ters. Since the energy transfer coefficients are unknown, they have been evaluated starting from the measured emission spectra of the bulk glass, reported in literature, and comparing their ratio with re-spect to the ratio between the simulated signal gain coefficients. The designed laser promises higher slope efficiency and power thresh-old lower than those obtainable with a holmium-heavily-doped fiber, having same fiber section geometry, same refractive indices and pumped at lambda(p) = 888 nm. Slope efficiency n = 16.67% and input power threshold Pth = 0.2 W are obtained for the fiber length Lfiber = 0.4 m, dopants concentrations NHo = 8 x 10(28) ions/m(3 )and N-Nd = 1 x 10(28 )ions/m3, and out-put mirror reflectivity Roat = 60%. This result encourages the fabrication of a continuous wave laser based on a Ho:Nd-codoped fluoroindate fiber.