Structural and Optical Coefficients Investigation of γ-Al2O3 Nanoparticles using Kramers-Kronig Relations and Z–scan Technique

ABSTRACT

γ-Al₂O₃ nanoparticles (NPs) with a mean diameter of 60 nm were prepared through the sol–gel technique and characterized by X-ray diffraction, field emission scanning electron microscopy (FESEM), and ultraviolet–visible (UV-Vis) spectroscopy. The formation of cubic structures with the γ phase for Al₂O₃ NPs confirms. The average particle size obtained is about 60 nm by the FESEM image. The nonlinear optical properties were examined by a single-beam Z-scan method using a Gaussian visible continuous wave Nd:YAG laser (532 nm). The Z-scan findings indicated a self-focusing nonlinearity and saturable absorption process in order of 10⁻⁸ (cm²/W) and 10⁻⁴ (cm/W) in the synthesized γ-Al₂O₃ NPs, respectively. Moreover, Kramers–Kronig relations were applied to determine the complex refractive index and dielectric coefficient of the specimens by Fourier-transform infrared spectroscopy. The transversal and longitudinal optical (TO and LO) modes are the two intersection points in the real and imaginary parts of the complex refractive index. Also, the maximum position of the Im(−1/ ε) plot is related to LO frequency