Nonlinear Optical Response from Excitons in Soliton Lattice Systems of Doped Conducting 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 doping.

Contribution

It models exciton effects in doped polymers using the SSH model with Coulomb interactions, analyzing the nonlinear optical response as a function of doping and system size.

Findings

THG magnitude increases by about 100 times with 10% doping

Large nonlinear enhancement is consistent across Coulomb strengths

Open and periodic systems show similar nonlinear behavior

Abstract

Exciton effects on conjugated polymers and the resulting optical nonlinearities are investigated in soliton lattice states. We use the Su-Schrieffer-Heeger model with long-range Coulomb interactions for electrons. 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 with 10 percent doping increases by the factor of about 10^2 from that of the neutral system. The large increase of the order two is common for several Coulomb interaction strengths, and is seen in open systems as well as in periodic systems.