Large third-order nonlinear optical response of a conjugated copolymer consisting of 2,5-diethynylthiophene and carbazole units

The third-order nonlinear optical (NLO) properties of a novel π-conjugated copolymer constituted of electron-rich carbazole and 2,5-diethynylthiophene have been studied using degenerate four-wave mixing (DFWM) at 1064 nm. The off-resonance second-order hyperpolarizability γ per repeated unit is estimated to be 2.2×10−31 esu; the nonresonant third-order susceptibility χ(3) approaches (8.6±1.7)×10−10 esu. The large ultrafast nonlinearity originates from an instantaneous electronic polarization.