Impact of Yb²⁺ on the anti-Stokes fluorescence cooling performance of Yb-doped silica fibers

To unlock the full potential of laser-cooled silica optical fibers, a better understanding of the internal mechanisms of heat generation is required. This work explores ytterbium-doped aluminosilicate fibers produced via industry-standard modified chemical vapor deposition (MCVD) techniques with varied levels of divalent ytterbium to determine their effect on anti-Stokes fluorescence thermal performance. The inclusion of Yb²⁺ is shown to have a significant negative impact on cooling potential. Yb²⁺ ions are shown to correlate with heat generation by two distinct mechanisms, absorption and quenching of active Yb³⁺ ions. This excess heating represents a reduction in quantum efficiency that is detrimental to Yb-doped fiber lasers and amplifiers beyond the laser-cooling application.