Femtosecond mode-locked laser at 1.5 μm region using topological semimetals NbAs nanosheets

For the first time, NbAs nanosheets are used as a saturable absorber for fiber laser mode locking, achieving high efficiency saturation absorption. NbAs nanosheets are prepared through a liquid-phase exfoliation method, and the following nonlinear optical testing is performed with a self-built twin balanced detection device, with a modulation depth of 3.92 %. Additionally, NbAs nanosheets are embedded in erbium-doped fiber laser as saturable absorber to produce stable laser output with excellent performance. NbAs nanosheets based saturable absorber can achieve a pulse width of 640 fs. Compared with other topological materials, weyl semi-metal NbAs nanosheets based saturable absorber shows narrower pulses and broader linewidths. Those results hold significant importance for exploring the potential applications of NbAs in ultrafast fiber lasers.