Femtosecond dynamics of the nonlinear optical response in polydiethynylsilane

We have measured the femtosecond dynamics of the nonlinear optical response χ(3) in polydiethynylsilane (C4H2SiBu2)x, a novel class of π‐conjugated polymers incorporating Si, using degenerate four‐wave mixing and photoinduced absorption techniques. In resonance conditions at 620 nm we found χ(3)=3×10−9 esu, which decays in a record time of 135 fs, followed by a slower decay component of 750 fs, without a long tail even at high laser intensities. This material is an excellent candidate for nonlinear optical devices in the sub‐THz frequency range.