Hafnium trisulfid nanosheets for ultrafast fiber laser

As a member of the transition metal chalcogenides family, hafnium trisulfid (HfS₃) has gained considerable interest in the realm of optoelectronics due to the distinctive optical and electronic properties. Notwithstanding this interest, there remains a paucity of comprehensive investigations into the saturable absorption characteristics and ultrafast laser applications of HfS₃. In this study, we employed a liquid exfoliation methodology to synthesize HfS₃ nanosheets, which were subsequently utilized to prepare a HfS₃-microfiber saturable absorber (SA). The SA exhibited a nonsaturable loss (αns) of 33.13 % and a modulation depth (αs) of 10.72 %. The dielectric properties of HfS₃ were studied theoretically. We integrated the fabricated HfS₃-microfiber into an Er-doped fiber (EDF) laser cavity in order to clarify the possible use of HfS₃ as a saturable absorber. Our findings demonstrate that the HfS₃-based SA produced mode-locked laser pulses with a narrow pulse duration of 492 fs and the signal-to-noise ratio (SNR) of 85 dB. Moreover, the fiber laser can operate in a Q-switching state with repetition frequency from 39.157 kHz to 113.93 kHz. Our work demonstrated that HfS₃ nanosheets have outstanding nonlinear properties and play an extremely important role in the field of ultrafast photonics.