Femtosecond photoexcitation dynamics in polydiacetylene 4BCMU film

Abstract Femtosecond pulses were used to study photoexcitation dynamics in polydiacetylene 4BCMU film. Ultrafast photoinduced dichroism and optical Kerr gate responses were observed. These measurements allowed estimation of the diffusion constant (D ∼ 0.1 cm2/s), the nonlinear index of refraction (n2 ∼ 10−8 esu), and third‐order susceptibility (δχ(3) ∼ 6 × 10−10 esu), in the film. We also found that the sign of the photoinduced transmission signal was dependent on the pump energy at the low energy absorption edge of the film. Possible explanations are proposed.