Optical Properties of 2D 3R Phase Niobium Disulfide and Its Applications as a Saturable Absorber

Abstract 2D van der Waals metal 3R phase niobium disulfide (3R‐NbS₂) has fascinating anisotropic, magnetic, optical, and superconducting properties. Herein, few‐layered 2D 3R‐NbS₂ nanosheets are fabricated by combining liquid phase exfoliation and spin‐coating methods. The first principles calculations are performed to explore their electronic band structures to reveal the metallic properties and enhanced optical absorption as thickness increased. The linear and nonlinear optical properties arising from the plasmonic effects and nonequilibrium electrons are studied through the violet–visible–near‐infrared absorption spectroscopy, polarization‐resolved optical microscopy, and open‐aperture Z‐scan methods. The nonlinear absorption coefficient and imaginary part of the third‐order susceptibility are determined to be −2.5 × 10⁶ cm GW⁻¹ and −2.4 × 10⁻⁶ esu at 1064 nm. Furthermore, 2D 3R‐NbS₂ nanosheets based saturable absorbers are fabricated and applied in solid‐state pulsed lasers, in which a continuous‐wave mode‐locking laser operation at 1050.6 nm is demonstrated with a pulse duration of 302 fs. The results not only verify that 2D metallic materials, such as 3R‐NbS₂, are excellent nonlinear optical modulators, but also will arouse a general interest in designing novel materials/structures with 2D metallic materials for electronic and photonic devices.