Nonlinear refractive index and three-photon absorption coefficient of poly(9,9-dioctylfluorence)

We investigate the optical Kerr effect and third harmonic generation (THG) arising from χ⁽³⁾ of poly(9,9-dioctylfluorence), which is an emerging organic π -conjugated polymer from the perspective of diverse optoelectronic applications. The measured nonlinear refractive index, obtained with closed-aperture Z-scan, is n₂ = (2.04±0.10) × 10^-12 esu at λ=1540 nm. Open-aperture Z-scan yields the three-photon absorption coefficient of γ= (1.88±0.26) × 10^-3 cm³ / GW² at λ=1064 nm, arising from χ⁽⁵⁾ response. The wavelength-dependent THG indicates that this semiconducting polymer can be a potentially useful polymer system for nonlinear-optics applications involving high-order optical processes in the mid-IR range.