Dual wavelength Q-switched cascade laser

A diode-cladding-pumped dual wavelength Q-switched Ho³⁺-doped fluoride cascade fiber laser operating in the mid-infrared is demonstrated. Stable pulse trains from the ⁵I6 → ⁵I₇ and ⁵I₇ → ⁵I₈ laser transitions were produced, and the μs-level time delay between the pulses from each transition was dependent on the pump power. At maximum pump power and at an acousto-optic modulator repetition rate of 25 kHz, the ⁵I₆ → ⁵I₇ transition pulse operated at 3.005 μm, a pulse energy of 29 μJ, and a pulse width of 380 ns; the ⁵I ₇ → ⁵I₈ transition pulse correspondingly produced 7 μJ pulse energy and 260 ns pulse width at 2.074 μm. To the best of our knowledge, this is the first demonstration of a Q-switched fiber laser operating beyond 3 μm.