A very large mode-area 2 wt% erbium-doped double-clad phosphate fiber with a core diameter of $60~\mu \text{m}$ and core numerical aperture of 0.03 was fabricated and used for the last stage amplifier of an all-fiber pulsed laser master-oscillator power amplifier (MOPA) at 1550 nm. The Er³⁺ double-clad phosphate fiber has a cladding-core ratio of 2.17 and a V number of 3.6 at 1550 nm. 3 mJ pulses with 21.5 ns duration were obtained with Gaussian-like spatial beam profile with only a 75 cm long phosphate gain fiber.

中文翻译：

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3 mJ 全光纤 MOPA，带有短长度高 Er3+ 掺杂磷酸盐光纤

纤芯直径为 2wt% 的掺铒双包层磷酸盐光纤 $60~\mu \text{m}$ 制造了 0.03 的核心数值孔径，并用于 1550 nm 的全光纤脉冲激光主振荡器功率放大器 (MOPA) 的末级放大器。Er ³⁺双包层磷酸盐光纤在 1550 nm 处的包层纤芯比为 2.17，V 数为 3.6。具有 21.5 ns 持续时间的 3 mJ 脉冲是通过类似高斯的空间光束轮廓获得的，只有 75 cm 长的磷酸盐增益光纤。