This work shows that the enhancement of higher-order harmonics from intentionally designed two-dimensional (2D) nanocrystals. The synthesis and exploration of adaptable 2D nanocrystals with excellent third-order nonlinear (NLO) properties are applied in various photonic applications. At present, the efficient HHG from the LIPs of pristine CsPbBr₃, four Ni-doped CsPbBr₃ with 0.03% Ni, 0.05% Ni, 0.08% Ni and 0.1% Ni, nanocrystals were demonstrated. The plasma plumes were produced by ablating the sample targets using ns and ps pulses.  

The materials ablated in a vacuum, the plasma plume contains components of parent material’s atoms, ions, nanoparticles, and clusters that could be responsible for the HHG. These components play an essential role in the generation of higher-order harmonics with respect to driving pulse intensities. The driving pulse intensity decides cut-off of harmonics as well its intensity of emitted harmonics due to dependence of ionization potential and ponderomotive potential of plasma components.

Yet it is challenging to identify exactly which components are responsible for HHG. However, during the experiments, by changing the delay between the ns ablating pulse and driving pulse, we can investigate the distribution of substances of different masses in the LIPs of these samples. In this case, the LIPs are generated with the ns ablating pulse where the temporal delay for the driving pulse could be adjusted electronically.

By combining the analysis of delay dependences of integrated harmonics signals and HHG spectra in the 20-100 nm wavelength range, the role of Ni-dopants, small- and large-sized 2D nanocrystals in the former process have been revealed.   

The present studies allowed a better understanding of the enhancement of plasma spreading dynamics in the harmonics generation from ablated species comprising similar Ni-dopants with a variable concentration.

The detailed results and observations have shown that, at optimal ablation of atoms and clusters, the laser-induced plasma produced on the surfaces of different Ni-doped and pure CsPbBr₃ 2D nanocrystals contained species spread out from targets with comparable velocities. 

The HHG yield was analyzed for two different cases. The enhancement of harmonics yields in the case of 800 nm driving pulse, ps LIPs was exactly comparative to the third-order NLO properties (nonlinear refractive index) of the samples. Similarly, this correlation was similar to LIPs of 2D nanocrystals using ns pulses.  

The emission of harmonics from LIP of these pristine and Ni-doped CsPbBr₃ NCs reported here supposedly provide the means to address the optimization of extreme ultraviolet radiations from structural differences.

The present work has been focused on the extrication role of Ni dopants in the release of intense harmonics from the plasma plumes using 800 nm as a driving laser beam. The tendency observed in the harmonic intensity development is comparable to the growth in NLO properties (i.e., n₂) of the same nanocrystals measured at a similar wavelength.