Experimental insights into increasing laser output at 2.8 µm in Er³⁺-doped zinc-tellurite fibers

In this paper, we provide a new experimental insight into the lasing process in the erbium-doped tellurite glass fiber at high diode-pump powers and pumping pulse durations. It is shown that lasing occurs at two wavelengths. Initially, at a fixed wavelength of 2.718 µm corresponding to the luminescence maximum, lasing takes place during the first ∼100 µs from the start of the pump pulse, while the main laser power occurs at the 2.8 µm for the rest of the pump pulse and shifts to longer wavelengths with increasing pump power. At pumping durations essentially exceeding the lifetime of the upper laser level, no self-termination of lasing occurs; on the contrary, the lasing power increases, which indicates the key role of the energy transfer upconversion (ETU) process. We demonstrate for the first time to our knowledge efficient lasing with an average power of 60 mW and a pulsed energy of 1.2 mJ in an erbium-doped zinc-tellurite fiber.