Three- and four-photon absorption in the single crystal polymer PTS

Summary form only given.Conjugated polymers belong to a class of materials that has proven to be one of the most fascinating and challenging developed to date for nonlinear optics. They, most specifically bis paratoluene sulfonate (PTS), have been shown to exhibit the largest third-order nonlinearities and the strongest two-photon absorption of any known material. The strong one- and two-photon absorption that occurs in PTS implies that the one- and two-photon active excited states might also be accessible through even higher order nonlinear processes that satisfy the same symmetry relations between the ground and excited states. Although there have been sporadic reports of three- and four-photon absorption in semiconductors, four-photon absorption has never been unambiguously measured in an organic solid-state material before. We report observation of three- and four-photon absorption in PTS at 1600 nm using the Z-scan technique.