Nonlinear Refractive Index in a Novel Nano-optical Material Based on the Nonconjugated Conductive Polymer, Poly($\beta$-pinene)

Two-photon absorption in a novel nano-optical polymer based on the nonconjugated conductive polymer, iodine-doped poly($\beta $-pinene) has been recently reported. In the present report, we will discuss measurement of the nonlinear refractive index (n$_{2})$ of iodine-doped poly($\beta $-pinene). The measurement has been made using 150 fs pulses from a Ti:Sapphire laser. Time-resolved measurement has been made using pump-probe technique in which the phase change in the probe beam was measured from the intensity-induced birefringence while the pump pulse was overlapped. The measured value of the nonlinear refractive index is larger than 10$^{-5}$cm$^{2}$/MW at 800 nm. The results show that the measured n$_{2}$ is of electronic origin. This exceptionally large magnitude of n$_{2}$ has been attributed to the special electronic structure of doped poly($\beta $-pinene) confined in a sub-nanometer domain.