Dual-regime passive pulse generation in a 2 µm laser using a HfSe 2 /MAPbI 3 heterostructure saturable absorber

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In this work, an HfSe 2 /MAPbI 3 heterostructure was employed for the first time as a saturable absorber (SA), to our knowledge, to realize both passive Q-switching (PQS) and passive mode locking (PML) in a 2 µm solid-state laser. High-quality multilayer HfSe 2 /MAPbI 3 nanosheets were prepared via liquid-phase exfoliation and integrated into the laser cavity by spin coating. Under PQS operation, a minimum pulse width of 584 ns, a peak power of 30.06 W, and an average output power of 2.08 W were achieved. Stable PML operation was also obtained at ∼1981nm, delivering a pulse duration of 989.5 ps, a repetition rate of 203.2 MHz, and an average output power of 0.92 W. These results demonstrate the excellent nonlinear optical modulation capability of HfSe 2 /MAPbI 3 and highlight its potential for high-performance 2 µm pulsed laser applications.