Mid-infrared fiber laser application: Er3+-doped chalcogenide glasses
Résumé
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 Ge20Ga5Sb10S65 doped with Er3+ (500 to 10000 ppm) were prepared by means of conventional melting and quenching method. The Er3+, widely studied in glass fibers for near-IR amplification, was initially selected for the transition 4I9/2 to 4I11/2 emitting at around 4.5 μm in order to demonstrate the ability of this sulfide composition for midinfrared fiber lasers application. In these objectives, absorption and emission spectra have been recorded and the radiative decay lifetime of excited levels (4I9/2, 4I11/2 and 4I13/2) 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 4I9/2 radiative quantum efficiency was estimated at 67 %. The emission cross-section was 2.6x10-21 cm2 at 4.6 μm obtained by Fütchbauer-Ladenburg theory. The product of measured lifetime and emission cross-section for 4I9/2 -> 4I11/2 transition is about 1.87x10-24 cm2.s is comparable with that for GaLaS glasses. The fiber drawing of the Er3+ doped Ge20Ga5Sb10S65 glasses and measurements of optical losses in mid-IR are currently in progress and first results were presented.