Indium selenide for Q-switched pulse generation in a mid-infrared fiber laser

Mid-infrared (mid-IR) pulse modulation components are extremely limited and are not very effective. By fabricating a novel broadband two-dimensional (2D) material, indium selenide (InSe), and adopting it as the passive saturable absorber (SA), we demonstrate a stable Q-switched Er-ZBLAN fiber laser at 2.8 μm. The stable Q-switching pulses can be maintained from the lasing pump threshold to the maximum pump power of 8.69 W, with the pulse repetition frequency ranging from 70.4 kHz to 253.2 kHz and the shortest pulse width of 423.2 ns. The obtained maximum value of average output power in this experiment is 712 mW, and the corresponding maximum pulse energy and peak power are 2.81 μJ and 5.71 W, respectively. The signal-to-noise ratio (SNR) of the laser output is 43.66 dB, which is larger than the majority of the passively Q-switched mid-IR fiber lasers reported so far. Besides, the nonlinear optical response at a mid-IR wavelength of ∼2.8 μm is also investigated. The experimental results demonstrate that the InSe material has great potential in mid-infrared pulse modulation and generation, and its performance can be comparable or even superior to the widely used SESAM.