WS₂ mode-locked ultrafast fiber laser

Graphene-like two dimensional materials, such as WS₂ and MoS₂, are highly anisotropic layered compounds that have attracted growing interest from basic research to practical applications. Similar with MoS₂, few-layer WS₂ has remarkable physical properties. Here, we demonstrate for the first time that WS₂ nanosheets exhibit ultrafast nonlinear saturable absorption property and high optical damage threshold. Soliton mode-locking operations are achieved separately in an erbium-doped fiber laser using two types of WS₂-based saturable absorbers, one of which is fabricated by depositing WS₂ nanosheets on a D-shaped fiber, while the other is synthesized by mixing WS₂ solution with polyvinyl alcohol, and then evaporating them on a substrate. At the maximum pump power of 600mW, two saturable absorbers can work stably at mode-locking state without damage, indicating that few-layer WS₂ is a promising high-power flexible saturable absorber for ultrafast optics. Numerous applications may benefit from the ultrafast nonlinear features of WS₂ nanosheets, such as high-power pulsed laser, materials processing, and frequency comb spectroscopy.