Fig. 1. Schematic illustration of different kinds of typical ultrathin 2D nanomaterials^[29].

Fig. 2. Optical limiting mechanisms: (a) Nonlinear scattering; (b) multi-photon absorption; (c) reverse saturable absorption; (d) free-carrier absorption^[11].

Fig. 3. (a) Synthesis of Au-Fe₂O₃-RGO composites; open aperture patterns of the samples at (b) 700, (c) 800, and (d) 900 nm^[35].

Fig. 4. (a) Synthesis of GO-Pt-1 and GO-Pt-2; (b) typical open-aperture Z-scan data and (c) optical limiting performance of the samples at 532 nm^[27]; (d) schematic illustration of the structure of PF-GO and ZnP-GO (insert shows the photographs of dispersions in DMF: (I) ZnTNP-PAES; (II) GO; (III) ZnP-GO; (IV) PF-GO; (V) PF-RGO; (VI) ZnP-RGO.); open-aperture Z-scan curves with normalized transmittance (open symbols) and scattering signal (solid symbols) for the samples at (e) 532 and (f) 1064 nm^[36].

Fig. 5. (a) Synthesis of PFTP-RGO. (b) Variation of the normalized transmittance as a function of input laser intensity for the films: (b1) at 532 nm; (b3) at 1064 nm; the corresponding β_eff coefficients as a function of the excitation pulse energy (b2), (b4)^[37].

Fig. 6. (a) Top view of the puckered honeycomb lattice of black phosphorus; (b) lateral view on the lattice in armchair direction. Insets: BP lattice with a six-membered ring in chair configuration highlighted in red; scanning tunneling electron microscopyimage of the BP lattice ^[42].

Fig. 7. (a)−(e) Typical open-aperture Z-scan data with normalized transmittance as a function of the sample positionZ for the samples embedded in PMMA matrix under the excitation of 6 ns pulses at λ = 532 with different energies. The solid lines are the theoretical fitting results. (f) Structure of BP:C₆₀ blends^[53].

Fig. 8. Open-aperture Z-scan fitted data of (a) BP-Big and (b) BP-Small; (c) NLO response of BP nanosheets with variable sizes BP-Big and BP-Small as a function of pulse fluence^[54]; open-aperture Z-scan results of the BP dispersion for nanosecond pulse excitation at (d) 532 nm and (e) 1064 nm and femtosecond pulse excitation at (g) 515 nm and (h) 1030 nm; (f) open-aperture Z-scan result and (i) corresponding scattering signal of BP dispersions at a 532 nm ns laser^[55].

Fig. 9. (a) Schematic illustration of the fabrication F₁₂PcZn-BP; (b) (I)−(III) typical open-aperture Z-scan data of the samples and (IV) variation in the normalized transmittance as a function of input laser intensity for the PMMA-based films at 532 nm^[56].

Fig. 10. Open (a) and closed (b) aperture Z-scan measurements of h-LiMoS₂ and MoS₂ at different input laser power, indicated at the top left of each curve, showing saturable absorption and self-focusing behavior of h-LiMoS₂ at a lower pumping power^[58].

Fig. 11. (a) Synthesis and (b), (c) NLO (OL) performance of MoS₂-PVK^[18,64]

Fig. 12. (a) Synthesis of MoS₂-PAN and pyro-MoS₂-PAN; (b) pyrolytic process of PAN; the Mo 3 d core level XPS spectra of (c) the non-annealed MoS₂-PAN and (d) the pyro-MoS₂-PAN. The 2 H and 1 T contributions are represented by red and green plots, respectively^[65,66].

Fig. 13. (a) Key structural factors that influence the properties of halide perovskites^[74]; (b) (I) representative crystal structures of halide perovskites in different dimensions; (II) nanoscale morphologies of halide perovskites; (III) schematic representation of the 2D organic-inorganic perovskites from different cuts of the 3D halide perovskite structure^[75].

Fig. 14. (a) Illustration of halide perovskites based NLO materials; (b) typical open-aperture Z-scan curves of CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x at 1064 nm; (c) typical open-aperture Z-scan curves of CH₃NH₃PbI₃ and CH₃NH₃PbI_3–xCl_x at 532 nm^[83].

Fig. 15. Typical open-aperture Z-scan data of the CH₃NH₃PbI₃:PVK/PMMA films with different CH₃NH₃PbI₃:PVK concentrations. The annealing condition: 200 ℃ for 30 min in N₂^[84].