Two-dimensional violet phosphorus as a broadband saturable absorber for mid-infrared photonics

Two-dimensional (2D) violet phosphorus (VP), a recently investigated 2D semiconductor material, is promising for advanced optoelectronic applications because of its distinct physical and chemical features. In this work, high-quality, few-layered, 2D VP nanosheets were prepared, and their nonlinear optical (NLO) absorption characteristics were examined in detail in the 2 and 3 μm bands. The calculated high nonlinear absorption coefficients, low saturation intensities, and high modulation depths of 2D VP nanosheets demonstrated their exceptional mid-infrared (MIR) saturable absorption properties and significant potential for MIR photonic applications. Thus, in the Tm: GdVO₄ laser and Er: YAP laser, we employed 2D VP as a broadband saturable absorber (SA), and obtained stable Q-switched pulse outputs with pulse durations of 522.6 ns at 1.9 μm and 195 ns at 2.8 μm, respectively. In particular, the pulse width obtained at 3 µm based on 2D VP-SA is much narrower compared to that obtained for most other 2D materials SAs. These results demonstrate that 2D VP can be a potential candidate for broadband MIR SA.