Low repetition rate gain-switched double-clad thulium-doped fiber laser operating in the 2 µm wavelength region

•Gain-switched laser of a TDF with cavity configuration based on a F9.•Stable gain-switched pulses with a pump repetition rate from 13 to 20 kHz.•Efficient suppression of the gain-switched secondary relaxation oscillations. The experimental demonstration of a gain-switched pulsed fiber laser with low repetition rate emission in the 2 µm wavelength region is presented. The laser cavity is based on the figure-9 shape, where the gain-switched operation of the laser is obtained by using a double-clad Tm-doped fiber (DCTDF) as gain medium and a commercial pulsed laser diode at 793-nm with configurable parameters as pump source. The pulse parameters of the pump source are optimized for efficient suppressing of unstable gain-switched laser oscillations. As a result, laser pulses with low repetition rate in a range from 10 to 20 kHz with laser emission at the wavelength of 1951 nm are obtained. The generated gain-switched pulses exhibit maximum duration and energy of 0.5 and 3.5 µJ, respectively. The delay time between the pump pulses and the gain-switched pulses is of ~ 0.5 µs.