Mid-infrared fiber laser application: Er~(3+)-doped chalcogenide glasses

摘要

Mid-infrared (IR) lasers are of interest for a variety of applications including environmental sensing, LIDAR and military counter measures. However, this wavelength range lacks powerful, coherent, robust and compact sources. A solution can lie in chalcogenide glasses as host materials for rare earth ions. With an extended infrared transparency, low phonon energy limiting the non radiative multiphonon relaxation rates and suitable rare earth solubility, sulfide glasses based on Ge-Ga-Sb-S system make available radiative transitions in the mid-IR range. The glasses with nominal composition of Ge_(20)Ga_5S_(10)S_(65) doped with Er~(3+) (500 to 10000 ppm) were prepared by means of conventional melting and quenching method. The Er~(3+), widely studied in glass fibers for near-IR amplification, was initially selected for the transition ~4I_(9/2) to ~4I_(11/2) emitting at around 4.5 μm in order to demonstrate the ability of this sulfide composition for mid-infrared fiber lasers application. In these objectives, absorption and emission spectra have been recorded and the radiative decay lifetime of excited levels (~4I_(9/2), ~4I_(11/2) and ~4I_(13/2) has been determined. These last experimental results were compared with those obtained by Judd-Ofelt model from absorption cross-sections of all observable transitions. Therefore, the ~4I_(9/2) radiative quantum efficiency was estimated at 67 %. The emission cross-section was 2.6×l0~(21) cm~2 at 4.6 μm obtained by Fuetchbauer-Ladenburg theory. The product of measured lifetime and emission cross-section for ~4I_(9/2) → ~4I_(11/2) transition is about 1.87×l0~(-24) cm~2.s is comparable with that for GaLaS glasses. The fiber drawing of the Er~(3+) doped Ge_(20)Ga_5Sb_(10)S_(65) glasses and measurements of optical losses in mid-IR are currently in progress and first results were presented.