Nonlinear Optical Response from Excitons in Soliton Lattice Systems of Doped Conjugated Polymers

Exciton effects on conjugated polymers are investigated in soliton lattice states. We use the Su-Schrieffer-Heeger model with long-range Coulomb interactions. The Hartree-Fock (HF) approximation and the single-excitation configurationinteraction (single-CI) method are used to obtain optical absorption spectra. The third-harmonic generation (THG) at off-resonant frequencies is calculated as functions of the soliton concentration and the chain length of the polymer. The magnitude of the THG at the 10 percent doping increases by the factor about 10 from that of the neutral system. This is owing to the accumulation ∗E-mail address: [email protected]; URL: http://www.etl.go.jp/People/harigaya/.