Nonlinear optical response from excitons in soliton lattice systems of doped conjugated polymers

TL;DR

This paper investigates the nonlinear optical response, specifically third-harmonic generation, in doped conjugated polymers with soliton lattice states, revealing significant enhancement due to exciton effects and soliton concentration.

Contribution

It introduces a detailed theoretical analysis of exciton effects on nonlinear optical properties in doped conjugated polymers using the SSH model with Coulomb interactions.

Findings

THG magnitude increases by about 100 times at 10% doping

Oscillator strengths accumulate at the lowest exciton with increased soliton concentration

Enhancement is consistent across different Coulomb interaction strengths

Abstract

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 configuration- interaction (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 10^2 from that of the neutral system. This is owing to the accumulation of the oscillator strengths at the lowest exciton with increasing the soliton concentration. The increase by the order two is common for several choices of Coulomb interaction strengths.