In-fiber resonantly pumped Q-switched holmium fiber laser

We demonstrate a double-clad fiber laser that incorporates a pump-light absorbing coaxially located Tm³⁺-doped outer core that reaches threshold and resonantly pumps an Ho³⁺-doped inner core. Under cw diode pumping, the output from the laser displays a pulse modulated behavior at wavelengths corresponding to the Tm³⁺ transition and short gain switched pulses from the Ho³⁺ core that have mode-locked characteristics. The Ho³⁺ and Tm³⁺ fiber lasers simultaneously produced 1.5 W across 2040-2140 nm and operate at a pulse repetition frequency of ∼80 kHz and at pulse widths as short as 330 ns.