Ultrasmall 2D NbSe₂ based quantum dots used for low threshold ultrafast lasers

Ultrasmall NbSe₂ quantum dots (QDs) with an average diameter of 2.68 nm were successfully fabricated and investigated. By employing the NbSe₂ quantum dots (QDs) as a saturable absorber, highly stable ultrafast laser pulse trains with a duration of 765 fs or 380 ps were successfully generated from mode-locking erbium or ytterbium-doped fiber laser systems by using the fabricated NbSe₂ QDs. The obtained laser pump power threshold for the mode-locking operation of the Er-doped fiber laser was 15 mW, which is the lowest value recorded among 2D materials based saturable absorbers. Our results give a promising contribution to the research field by demonstrating the strong nonlinear optical properties of these novel ultrasmall NbSe₂ QDs. It also opens up new opportunities for the use of these novel materials for nonlinear optics and ultrafast laser photonic technologies.