Influence of Post-Annealing Treatments on Third-Order Nonlinear Optical Properties in ZnO Thin Films

This study explores the impact of annealing temperature (TA) on the sol-gel-deposited ZnO thin‑films’ nonlinear optical characteristics on glass substrates. By examining the surface topography with Atomic Force Microscopy (AFM), samples that were annealed at 450°C were found to have the ideal surface smoothness of 9.27 nm. Utilising the second harmonic output of a Nd:YAG laser, the Z-scan technique, UV‑Vis-NIR transmission, and X-ray diffraction (XRD) were employed in the analysis of the films. The materials’ nonlinear optical (NLO) characteristics revealed that the annealing temperature had a significant impact. Notably, the maximum nonlinear optical susceptibility, χ⁽³⁾, was achieved at an annealing temperature of 450°C, indicating a direct correlation between thermal processing and the enhancement of NLO performance.