Theoretical study of optical pockels and Kerr coefficients of polyenes

摘要

We report here the numerically exact Pockels' and Kerr's coefficients of polyenes within the Pariser-Parr Pople Model. We have computed the model exact polarizability of polyenes of chain length, N $EQ 6, 8 and 10 at various static electric fields and excitation frequencies. From a 3rd degree polynomial fit of the model exact polarizability ($beta@(approximately ega@; approximately ega@,O) (linear term) and $tau@(approximately ega@; approximately ega@,O,O) (2nd order term) are obtained. The Pockels and Kerr coefficients are calculated from $beta and $tau@. In polyenes the Pockels coefficients are small and the Kerr coefficients dominate and are the largest when the field is applied along the chain axis. The coefficients, $alpha@(approximately ega@; approximately ega@), $beta@(approximately ega@; approximately ega@,O) and $tau@(approximately ega@; approximately ega@,O,O) all increase with chain length. $alpha@(approximately ega@; approximately ega@) and $tau@(approximately ega@; approximately ega@,O,O) have the usual power law dependence and have exponent values at 1.54 and 3.78 respectively which are in agreement with the values reported in the literature. The coefficients $alpha@(approximately ega@; approximately ega@), $beta@(approximately ega@; approximately ega@,O) and $tau@(approximately ega@; approximately ega@,O,O) increases with increase in the excitation frequency, for frequencies below the two photon resonance value.