STATIC AND DYNAMIC 3RD-HARMONIC GENERATION IN LONG POLYACETYLENE AND POLYPARAPHENYLENE VINYLENE CHAINS

We have calculated the full spectrum of the third-order optical susceptibility, chi(3)(-3-omega;omega,omega,omega) in long oligomers of polyacetylene and polyparaphenylene vinylene, in tbc framework of a simple one-electron tight-binding approach. All doubly excited states are explicitly included in a sum-over-states formulation. The damping factors associated with resonances with excited states are modulated as a function of excited-state energy. Both the length dependence and the dynamic behavior of chi(3)(-3-omega;omega,omega,omega) are found to be in excellent agreement with experiment. Our results thus show that, contrary to the situation in very short polyenes, a one-electron theory can provide an accurate description of the nonlinear optical response in conjugated polymers.