Third-order nonlinear mixing in polydiacetylene solutions

Abstract
Third‐order mixing has been measured in solutions of the polydiacetylenes. The Raman molecular vibration contribution to the third‐order susceptibility χT(3) (−ω3, ω1, ω1, −ω2) has been characterized completely. A surprisingly strong polymer two‐photon absorption contribution to χT(3) was found. The cross section for two‐photon absorption at 2ω1=32 000 cm−1 is 6×10−47 cm4 sec photon−1 (polymer repeat unit)−1. The polymer nonresonant susceptibility could not be determined because of the strong two‐photon contribution to χT(3).