Abstract

We study the thermal bleaching process of photodarkening-induced loss in ytterbium-doped fibers. The observed power-law time dependence of the normalized absorption coefficient is well represented by the thermal decay model of Erdogan et al. [J. Appl. Phys. 76, 73 (1994)] . Using this model, we derive the activation energy associated with thermal recovery of the induced loss to prephotodarkened state. For the studied commercial $20\mu \mathrm{m}$ core diameter large-mode-area fiber, the energy distribution consists of a single peak, located at $1.32\mathrm{eV}$ with a FWHM of $\sim 0.31\mathrm{eV}$. The results presented are of particular importance to understanding photodarkening and bleaching processes in high-power fiber lasers.

© 2009 Optical Society of America

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