PdX₂ (X = S, Se) saturable absorbers for passively Q-switched Er:YAP laser at 3 μm

In this work, two-dimensional (2D) PdX₂ (X = S, Se) nanosheets were successfully fabricated via the ultrasound-assisted liquid-phase exfoliation (LPE) method and characterized comprehensively. Employing open-aperture (OA) Z/I-scan techniques, the nonlinear absorption (NLA) properties of the samples in the mid-infrared (MIR) region were systematically investigated, which revealed that PdX₂ (X = S, Se) nanosheets exhibited excellent saturable absorption characteristics at 3 μm. The large effective NLA coefficient, high modulation depth, and low saturation intensity highlight their potential as high-performance saturable absorbers (SAs). Subsequently, to the best of our knowledge, PdX₂ (X = S, Se) were used as SAs (PdS₂-SA, PdSe₂-SA) to demonstrate a passively Q-switched (PQS) Er:YAP laser at 3 μm for the first time. Stable pulsed outputs were achieved with the shortest pulse durations of 525 ns and 369 ns at repetition rates of 93.22 kHz and 106.02 kHz, respectively, for PdS₂-SA and PdSe₂-SA. These results demonstrate that PdX₂ (X = S, Se) are promising candidate materials for SAs in the MIR pulsed laser systems, while also revealing the significantly enhanced NLA and optical modulation characteristics of PdSe₂ compared to PdS₂.