2.6 mJ energy extraction in nanosecond duration from an actively Q-switched Er³⁺-doped fluoride fiber oscillator at 2.785 μm

In this Letter, we experimentally report direct generation of millijoule-level nanosecond pulses from an actively Q-switched Er³⁺-doped fluoride fiber oscillator at 2.785 μm. By employing a relatively long large-core active fiber to enhance energy storage capacity and a specially designed cavity for suppressing parasitic lasing of such a high-gain system, clean Q-switching with a pulse width of 74 ns has been achieved, yielding a maximum energy of 1.9 mJ with a peak power of 24 kW at the repetition rate of 100 Hz. If excluding the parasitic lasing mixed with the Q-switched pulses, the extracted pulse energy can be further boosted to 2.6 mJ under single-transverse-mode condition with the increased pump power, leading to a reduced pulse width of 55 ns and an improved peak power of 44 kW at an optical-to-optical efficiency of 3.5%. To our knowledge, the extracted pulse energy represents to date the highest level of all the nanosecond fiber laser systems in the mid-infrared region.