Thickness-dependent nonlinear optical properties of ITO thin films

The nonlinear absorption (NLA) properties of ITO thin films were performed by utilizing femtosecond (100 fs), a high-repetition rate (80 MHz), and near-infrared (NIR) (750–820 nm) laser pulses. A radio frequency (RF) magnetron sputtering system was used to prepare ITO thin films of two different thicknesses. A scanning electron microscope was used to determine the film thickness and a UV–Visible spectrophotometer was used to observe the linear optical properties of the thin films. The open aperture Z-scan technique's nonlinear absorption studies of ITO thin films exhibited a reverse saturable absorption. The NLA properties of the ITO films varied depending on ITO thickness, incident laser power, and excitation wavelength, attributed to the increasing localized defect states in the band gap. The results showed that increasing the excitation wavelength from 750 to 820 nm reduces the nonlinear absorption coefficient of the ITO thin films from 15.88 × 10⁻⁷ to 9.43 × 10⁻⁷ cm/W and from 6.72 × 10⁻⁷ to 5.15 × 10⁻⁷ cm/W at ITO thicknesses of 280 and 170 nm, respectively. In contrast to the film thickness, the nonlinear absorption coefficient was inversely proportional to the excitation laser wavelength. Additionally, the optical limiting of ITO thin films was investigated, and it was found that there is a clear correlation between optical limiting and thin film thickness.