Thermal processes are key limiting factors to power scaling in high-power fiber lasers. Heat generation can arise from the quantum defect, partly manageable through judicious selection of pumping and lasing wavelengths. Heat can also result from nonradiative processes, presently believed to be the main obstacle to efficient anti-Stokes fluorescence cooling in silicates. Therefore, it is meaningful and necessary to evaluate the quantum conversion efficiency (QCE), which is defined to be the fraction of pump photons that undergo the desired radiative process. Here, an accurate and sensitive Brillouin-based method to characterize the QCE in Yb-doped optical fiber is proposed and evaluated.
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