Third-order optical nonlinearities and high-order harmonics generation in Ni-doped CsPbBr3 nanocrystals using single- and two-color chirped pulses

Abstract: Organic–inorganic lead halide perovskite nanocrystals (NCs) have received the phenomenal attention of researchers in the last few years due to their advanced optical properties and developments in simple synthetic procedures. In this work, we demonstrate the effect of Ni-dopant on the ultrafast third-order nonlinear optical (NLO) properties of two-dimensional (2D) CsPbBr₃ NCs using 60 fs laser pulses at a wavelength of 400 nm. Based on the probe pulse intensity, pure CsPbBr₃ NCs exhibited saturable absorption and reverse saturable absorption (RSA). The doping of NCs by Ni at different concentrations significantly modified the nonlinear absorption mechanism where the RSA was followed by the SA with growing input laser intensity. The nonlinear refractive index of Ni-doped CsPbBr₃ NCs decreased when compared with the pure CsPbBr₃. In addition, the NLO properties of these 2D NCs are correlated with the efficiency of the high-order harmonics generated during propagation of the two-color (800 + 400 nm) and single-color (800 nm) chirp-free (35 fs) and negatively/positively chirped pulses through the laser-induced plasmas produced on the surface of undoped and Ni-doped perovskite NCs. The ablation of Ni-doped NCs allowed increasing the harmonic yield compared to undoped CsPbBr₃ NCs. Our studies undoubtedly demonstrate the advanced lower and higher order NLO properties of Ni-doped 2D CsPbBr₃ NCs. Graphical abstract: [Figure not available: see fulltext.]