Optical dispersion of a metallic VO2 film in the near IR range

A VO2 film on glass, when continuously heated to 350 K, exhibits self-focusing and saturable absorption behavior towards femtosecond radiation in the near-infrared range, indicative of an electronic response rather than a thermo-optical effect. Using the Adomian Decomposition Method (ADM), we developed four nonlinear optical models with different saturation intensity coefficients to analyze open-aperture Z-scan measurements. Our results show significant contributions from both bound and free electrons to the nonlinear susceptibility, with the bound-electron nonlinear refractive index ~ n2 (350 K) = 1.69 ± 0.19 cm2/TW and the free-carrier part ~ δr(350 K) = 1.2·10-22 cm3. These findings are crucial for designing all-optical phase modulation devices, and essential for advanced optical components such as switches, modulators, and sensors.