Holmium, praseodymium-doped fluoride fiber laser operating near 2.87 μm and pumped with a Nd:YAG laser

The operation of a single-clad Ho³⁺, Pr³⁺-fluoride [zirconium, barium, lanthanum, aluminum, and sodium (ZBLAN)] fiber laser pumped by an Nd: yttrium-aluminum-garnet (YAG) solid-state laser operating at 1064 nm has been demonstrated. An output power of more than 600 mW was generated at a slope efficiency of 9% after a threshold of ∼ 200 mW was reached. The center wavelength was 2854 nm for low-launched powers of < 2 W and was shifted to 2874 nm for higher launched pump powers. Excitation is predominantly into the Ho³⁺ (⁵I₆) level, with the Pr³⁺ acting to deplete the Ho³⁺ lower laser level. The relatively small slope efficiency and low output power is attributed to the small absorption coefficient of Ho³⁺ at 1064 nm, as well as to the additional loss that was caused by excited-state absorptions (ESAs) at the pump wavelength from both Ho³⁺ and Pr³⁺ ions.