Optical nonlinearities in polymeric materials

Summary form only given. The results of an experimental study into the fundamental, nonlinear optical properties of the polydiacetylene group of organic, polymeric materials are presented. The aim is a comprehensive spectral study using systematically chosen samples in order to gain understanding of the materials and to evaluate their feasibility for technological application. A sub-picosecond laser system was utilised to carry out a particular range of experiments within three spectral regions. Two- and three-beam experiments were used to obtain information on the magnitude and dynamics of the nonlinear response of the materials. Four specific spectral regions have been identified: on-resonance absorption saturation occurs due to phase-space filling of excitons; induced absorption nearer resonance; at longer wavelengths two-photon absorption cuts in and between induced and saturated absorption there is a transition region within which the imaginary part of the third-order susceptibility changes sign. A theoretical model has been developed which accurately describes the absorptive nonlinear behaviour.<>