A tunable Q-switched Ho3+-doped fluoride fiber laser

A tunable actively Q-switched cascade Ho³⁺-doped fluoride fiber laser operating in the mid-infrared region is demonstrated. Using a planar diffraction grating in the Littrow configuration for tuning, stable pulse trains from the ⁵I₆ → ⁵I₇ transition were observed over a 80 nm tuning range from 2.95 to 3.031 μm with a bandwidth of ∼1 nm. Gain-switched pulse trains from the ⁵I ₇ → ⁵I₈ transition at 2.074 μm induced by the ⁵I₆ → ⁵I₇ Q-switched pulses were also produced over the entire tuning range. At maximum pump power and at an acousto-optic modulator repetition rate of 40 kHz, >15 μJ pulse energy and 300-410 ns duration pulses were obtained from 2.97 μm to 3.015 μm, respectively. To the best of our knowledge, this is the first tunable Q-switched pulsed fiber laser operating in the mid-infrared region.