Saturable absorption properties and ultrafast photonics applications of HfS.

In this Letter, we focus on investigating the ultrafast photonics applications of two-layer HfS nanosheets. We prepared two-layer HfS nanosheets and carried out experiments to study their nonlinear saturable absorption properties. The results showed that the two-layer HfS-based saturable absorber exhibited a modulation depth of 16.8%. Additionally, we conducted theoretical calculations using first principles to estimate the structural and electronic band properties of the two-layer HfS material. Furthermore, we utilized the two-layer HfS materials as SAs in an erbium-doped fiber cavity to generate mode-locked laser pulses. We measured a repetition frequency of 8.74 MHz, a pulse duration of 540 fs, and a signal-to-noise ratio of 77 dB. Overall, our findings demonstrate that the two-layer HfS material can serve as a reliable saturable absorber, possessing properties comparable to currently used two-dimensional materials. This expands the application fields of HfS materials and highlights their potential for advanced optoelectronic devices.