Ultrafast Laser-Assisted Synthesis of AlCuNi Nanoparticles for Nonlinear Photonic Applications: Effect of Pulse Energy on the Structure, Composition, and Nonlinear Optical Responses

We report on the synthesis of AlCuNi nanoparticles (NPs) using the laser processing of colloids composed of a mixture of laser-generated monometallic NPs. The effect of laser processing energy on the structure, morphology, composition, and optical properties of the synthesized NPs was investigated systematically by using microscopic and spectroscopic techniques. Transmission electron microscopy (TEM) revealed a reduction in particle size with an increase in processing energy. TEM also revealed a core–shell (CS) structure at a low processing energy, which disappeared as the energy was increased. STEM–EDS, HRTEM, and SAED analyses demonstrated that the elemental composition and spatial distribution of Al, Cu, and Ni strongly depend on the applied laser energy, resulting in distinct composition inhomogeneities at low and high energies. Near-homogeneous AlCuNi alloy NPs with improved compositional uniformity were achieved at an optimal pulse energy of 300 μJ, identifying this condition as most favorable for effective alloying. These studies revealed that the interplay between the physicochemical and thermodynamic properties of the constituent elements (including melting and vaporization enthalpies, surface energies, atomic radii, and mixing enthalpies) and the laser energy governs the alloy formation. UV–visible absorption and photoluminescence spectra exhibited energy-dependent shifts and peak broadening, indicating enhanced interparticle interactions at higher energies. Nonlinear optical (NLO) properties assessed by femtosecond Z-scan measurements showed reverse saturable absorption and self-focusing behavior driven by intrinsic three-photon absorption (3 PA) in the AlCuNi NPs system. The observed 3 PA, reverse saturation absorption, and self-focusing behavior demonstrate that laser-synthesized AlCuNi NPs are promising candidates for nonlinear photonic applications under ultrafast laser excitation. The results obtained highlight the critical role of laser processing energy in tailoring the structural, compositional, morphological, and optical properties of the AlCuNi NPs. Furthermore, based on the experimental results, a possible growth mechanism for the different morphologies and phases of AlCuNi NPs obtained during laser processing at different energies is elucidated.