Spectrally resolved third-order nonlinearities in polydiacetylene microcrystals: influence of particle size

Abstract

The on- and near-resonant third-order nonlinear optical response of polydiacetylene microcrystals in suspension was studied by the Z-scan technique with tunable picosecond pulses. The absorptive and refractive contributions to the excitonic-dominated nonlinearity were fully resolved at several wavelengths. Microcrystals of two different average sizes were studied, and a comparison of their nonlinear coefficients was made. A three-level model for the nonlinear response is presented that shows good agreement with the experimental data.