Influence of annealing temperatures on the nonlinear optical performance of fluorine-doped tin oxide thin film

Fluorine-doped tin oxide (FTO) thin films exhibit potential applications in photonic devices, owing to their superior transparency, conductivity, and adjustable nonlinear optical response. In this study, FTO films were prepared through magnetron sputtering, and the influence of annealing temperature on their crystalline structure and third-order nonlinear optical properties was systematically investigated. The results indicate that annealing enhances the carrier concentration from 0.93 × 10 20 cm -3 to 1.03 × 10 20 cm -3 . Z-scan measurements confirm that the film annealed at 700 °C exhibits optimal nonlinear parameters with a nonlinear absorption coefficient of –5.7 × 10 −9 m/W and a nonlinear refractive index of 6.9 × 10 −16 m 2 /W. The third harmonic generation conversion efficiency increases with annealing temperature. This research clarifies the mechanism driven by carrier dynamics that underlies the annealing-induced nonlinear enhancement in FTO, and offers a robust materials foundation for the development of ultrafast all-optical modulators, high-sensitivity nonlinear sensors, and on-chip frequency converters.