Optical properties of Yb+3-doped fibers and fiber lasers at high temperature

Recent advances in power scaling of Yb+3-doped fiber lasers to the kilowatt level suggest a need to examine the performance of Yb+3-doped silica at temperatures well above ambient. We report experimental results for the absorption coefficient, emission cross-section, fluorescence lifetime, and slope efficiency of a Yb3+-doped large mode area (LMA) silica fiber for temperatures spanning 23 degrees C-977 degrees C. To the best of our knowledge these are the highest temperatures to date for which these optical properties have been measured. We find a sharp reduction in the energy storing capability and lasing performance of Yb+3:SiO2 above 500 degrees C that coincides with the onset of non-radiative transitions in the excited state manifold (thermal quenching). As the temperature increases from room temperature to 977 degrees C, absorption in the 1020-1120 nm operating band increases monotonically, concurrent with a reduction in absorption at the 920-nm and 977-nm pumping bands. Conversely, the spectral weight of the emission cross-section shifts from transitions above 1010 nm to those below, with the exception of the 977-nm emission band. (C) 2011 Elsevier B.V. All rights reserved.