Identification and Role of Two-Photon Excited States in a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi></mml:math>-Conjugated Polymer

Abstract

We have measured the full two-photon absorption (TPA) spectrum in the transparency range of single-crystal polydiacetylene paratoluene-sulfonate (PTS) using $z$ scan. The spectrum consists of three well-defined two-photon excited states superimposed on a continuum of even-parity states. Comparison of the TPA and the one-photon absorption spectra identifies a two-photon accessible state as the lowest excited state of PTS. The accompanying dispersion in the intensity-dependent refractive index coefficient ${n}_{2}$ is also reported.