Mo_4/3B₂T₂/TiO₂ vdW heterostructure as saturable absorber for ultrafast pulse generation

Van der Waals heterostructure have garnered significant interest in ultrafast laser generation because of their attractive saturable absorption properties, holding promise for application in optics, medicine, and optoelectronics. In this study, the saturable absorption properties of TiO₂, Mo_4/3B₂T₂, and Mo_4/3B₂T₂/TiO₂ vdW heterostructure SAs are investigated. The integration of the SAs into the cavity reveals the observation of fundamentally conventional solitons. The output characteristics of conventional solitons based on three SAs are recorded. These results suggest that the saturable absorption of Mo_4/3B₂T₂/TiO₂ vdW heterostructure is enhanced obviously compared with that of Mo_4/3B₂T₂ and TiO₂. Furthermore, 2nd-, 4th-, and 5th-order harmonic solitons are achieved, corresponding to the repetition rate of 20.36 MHz, 42.71 MHz, and 53.39 MHz, respectively. We established a model in order to understand the saturable absorption properties of the Mo_4/3B₂T₂/TiO₂, which suggests the enhancements of the saturable absorption are attributed to the carrier migration between Mo_4/3B₂T₂ and TiO₂. Our results indicate that Mo_4/3B₂T₂/TiO₂ vdW heterostructure can be used as an excellent nonlinear optical material, which can be used as an SA in ultrafast pulse generation.