Compact self-Q-switched green upconversion Er:ZBLAN all-fiber laser operating at 543.4 nm.

We report the demonstration of a compact self-Q-switched green upconversion Er³⁺:ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) fiber laser operating at 543.4 nm. The all-fiber green laser simply consists of a 45 cm high-concentration Er³⁺:ZBLAN fiber, a 976 nm pump source, and a pair of fiber end-facet mirrors. Under the strong excitation of the 976 nm pump laser, green upconversion lasing at 543.4 nm is achieved from the compact Er³⁺:ZBLAN fiber laser. Interestingly, the green laser exhibits stable self-Q-switching operation. As the 976 nm pump power is increased, the pulse repetition rate linearly increases from 25.9 to 50.8 kHz and the pulse width narrows from 7.2 to 1.95 μs. The Q-switched green laser has a pump threshold of 118 mW and a maximum output power of 6.9 mW with a slope efficiency of 30%. This is, to the best of our knowledge, the shortest-wavelength operation of a self-started or passively Q-switched fiber laser.