Third‐Order Nonlinear Optical Response of Few‐Layer MXene Nb₂C and Applications for Square‐Wave Laser Pulse Generation

Abstract

Abstract Niobium carbide (Nb 2 C), a newly developed 2D MXene material, has attracted much attention due to its outstanding electronic and optical properties. In this work, few‐layer 2D Nb 2 C nanosheets are synthesized by magnetron sputtering deposition method. Z‐scan measurements with pump source operating at 1.0 µm are performed to study the third‐order nonlinear optical response, revealing excellent light modulation capabilities of 2D Nb 2 C. The effective nonlinear absorption coefficient (β eff ≈ –10 5 cm GW –1 ) caused by saturable absorption effect is determined to be two orders of magnitude larger than that induced by reverse saturable absorption processes (two‐photon absorption, etc.). The positive nonlinear refractive index n 2 is determined to be ≈10 –13 m 2 W –1 for the first time. Moreover, by decorating 2D Nb 2 C onto microfiber, microfiber‐based 2D Nb 2 C saturable absorber is fabricated and applied for compact square‐wave pulse mode‐locking ytterbium‐fiber laser. The pulse duration of SWP increases from 0.652 to 1.616 ns with the pulse energy increasing linearly up to 0.89 nJ while the peak power remains a constant. The results not only verify the capability of 2D Nb 2 C as an optical modulator, but also pave a new way for exploring SWP laser sources.