Third-order optical nonlinearity at excitonic resonance in poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene)

The optical properties of polythiophene have generated widespread interest. Because this material shows high electronic conductivity by doping and demonstrate large third-order optical nonlinearity |χ⁽³⁾|, it may be applicable as an active material in electro-optical devices. Recently, we reported the enhancement of third-order optical nonlinearity in poly(3-hexylthiophene) (P3HT) by the control of regularity in the polymeric structure. The enhancement is due to increasing the conjugation length. In the present study, we use the thin films of poly(3-[2-(S)-2-methylbutoxy)ethyl]thiophene which is expected to have large conjugation length. We measured |χ⁽³⁾ |I at excitonic resonance using degenerate four-wave mixing, and estimate the conjugation length of samples