Green Wavelength-Tunable and High Power Ho3+-Doped Upconversion Fiber Lasers

Tunable coherent light source emitting at the visible region has long been recognized as a key asset, especially with a monolithic design involved, for the increasing number of emerging applications in the scientific research and industrial manufacturing. Here, an efficient 640 nm solid-state laser is used as a pump source, and the fiber end-facet mirrors construct a fiber laser resonator. We experimentally developed green wavelength-tunable Ho
³⁺
-doped all-fiber upconversion lasers, which corresponds to the transitions originating from the Stark levels within thermally-coupled
⁵
S2,
⁵
F4 states and terminating on the
⁵
I8 ground state. Moreover, a high power 236 mW and a high efficiency 38.9% of green upconversion fiber laser operating at 544 nm was demonstrated, and the output power achieved is six-times higher than before. Such compact tunable and high power green fiber lasers are very attractive for the practical applications in optical communications, spectroscopy, sensing, and optical switching devices.