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According to the modeling of ion pairs in high-concentration erbium-doped fiber lasers, a closed form rate and power evolution equations containing isolated ions and ion pairs are constructed. Based on the equations, the effects of ion pairs on the output performance of high-concentration erbium-doped fiber lasers for low Q and high Q laser cavity in three different pump modes are analyzed numerically. The results show that with the increasing percentage of ion pairs, the output power and the slope efficiency decrease, and the threshold increases for each pump mode. Meanwhile, the backward pump mode is proved to be the best pump mode and the deleterious effects of ion pairs for low Q laser cavity is proved to be smaller than that for high Q laser cavity. [ABSTRACT FROM AUTHOR]

Based on the special structure of high-power Yb3+-doped double-clad fiber lasers, a heat dissipation model and the corresponding steady-state heat equations with consideration of both convective and radiative heat transfer are constructed. The temperature distributions along the radial and axial directions of the fiber for forward pump of 1000 W and two-end pump of 500 W each side are calculated numerically by using the steady-state rate equations and the heat equations. The results show that the temperature distribution for two-end pump mode is more even than that for forward pump mode and the maximum temperature in the fiber decreases by 139.8°C. Finally, a comparison between the temperature distributions with and without consideration of radiative heat transfer is performed, the results of which indicate that radiative heat transfer plays an important role in heat dissipation of high-power fiber lasers. Therefore, radiative heat transfer has to be considered in the thermal, stress, and thermo-optic effects of any type of high-power fiber lasers. [ABSTRACT FROM AUTHOR]