NiPS₃ nanoflakes: A nonlinear optical material for ultrafast photonics

Ultrafast photonics based on two-dimensional (2D) materials has been used to investigate light-matter interactions and laser generation, as well as light propagation, modulation, and detection. Here, 2D metal-phosphorus trichalcogenides, which are known for applications in catalysis and electrochemical storage, also exhibit advantageous photonic properties as nanoflakes that are only a few layers thick. By using an open-aperture Z-scan system, few-layer NiPS₃ nanoflakes exhibited a large modulation depth of 56% and a low saturable intensity of 16 GW cm^-2 at 800 nm. When NiPS₃ nanoflakes were used as a saturable absorber at 1066 nm, highly stable mode-locked pulses were generated. Thus, these results revealed the nonlinear optical properties of NiPS₃ nanoflakes which have potential photonics applications, such as modulators, switches, and thresholding devices.