Modeling and characteristics of high-power gain-switched Ho3+-doped fiber laser at ∼ 3.9 μm with cascade pumping

In this paper, we propose a gain-switched Ho³⁺-doped fiber laser to realize high-power nanosecond pulsed laser emission at ∼3.9 μm by leveraging a continuous-wave (CW) pump source at ∼1.95 μm and a pulsed pump source at ∼1.66 μm. Numerical investigation is carried out to analyze the influences of different pump parameters on the laser output performance. Moreover, stable single-pulse operation range is predicted under various average pump powers, pulse widths, and repetition frequencies of the 1660 nm pump source. Stable single-pulse operation is achieved with the average power of 1.08 W and laser pulse energy of 10.87μJ, which are both an order of magnitude improvement over the ones obtained with conventional single wavelength pumping at 888 nm, and also reach the level of the more maturely developed gain-switched Er³⁺ and/or Dy³⁺ doped fiber lasers with laser emission at shorter wavelengths of 2.8 μm, 3.2 μm and 3.5 μm. The pulse width and repetition frequency of the output laser are 18.72 ns and 100 kHz, respectively. The proposed gain-switched cascade pumped Ho³⁺-doped fiber laser is a promising approach for the realization of high-power and high-energy fiber laser emission at the important ∼3.9 μm mid-infrared wavelength.