Nonlinear optical response of excitons confined to one dimension

Abstract

We present femtosecond time-resolved transient reflectivity measurements on polydiacetylene performed at the peak of the exciton resonance. The magnitude of the nonlinear refractive index at 1.97 eV was found to be 3.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ ${\mathrm{cm}}^{2}$/W. We discuss a model which accounts quantitatively for the large resonant and nonresonant optical nonlinearity observed in polydiacetylene in terms of phase-space filling by one-dimensional excitons.