Few-layer Ta₂CT_x nanosheets-based mode-locked fiber lasers

In this paper, two-dimensional (2D) few-layer Ta₂CT_x nanosheets are fabricated by liquid phase exfoliation (LPE) method. The nonlinear optical absorption properties are studied by Z-scan and I-scan techniques, revealing excellent saturable absorption response with an effective nonlinear absorption coefficient of -92.2 cm/MW@1064 nm. The saturation intensity and modulation depth for 1064 nm and 1550 nm are determined to be 79 and 51 MW/cm², 9.9% and 4.5%, respectively. Furthermore, by decorating few-layer Ta₂CT_x nanosheets onto microfiber, few-layer Ta₂CT_x saturable absorber (SA) is fabricated and applied in Yb-doped and Er-doped fiber lasers (YDFLs and EDFLs). Not only a normal mode-locked operation but also square-wave pulse (SWP) are realized by increasing the length of the laser cavity at 1.5 µm, highlighting the great potential of few-layer Ta₂CT_x nanosheets as an optical modulator. The maximum pulse duration of 5.56 ns is also the widest SWP width that can be realized with 2D materials without filtering device in the cavity. Our work provides a platform for exploring novel SAs materials and nonlinear phenomena in mode-locked fiber lasers.