Two-Photon Absorption of Biexcitons for a Truncated Potential

ABSTRACTA tight binding, one dimensional, two-band model is used to investigate the formation and nonlinear optical properties of biexcitons in conjugated polymers. The full single and double electron-hole pair basis sets are explicitly considered for a Hamiltonian which includes an electron and hole transfer parameter (t) along with a truncated potential with only on-site (V0 ) and nearest neighbor (V1) Coulombic interactions. The biexciton phase space is determined to be a function of only two parameters α and βwhere α ≅V1/V0 and β ≅t/V0. Due to the truncated potential only a single biexciton eigenstate is formed in the region limited by 0.64 < α≤ 1 and 0 ≤ β< 0.33. The two-photon absorption spectra in the range 0 < hω < δ, where δ is the one photon gap, are found to contain at most two types of peaks: one arising from a biexciton and another due to a charge-transfer, single-exciton. The polymer limit is obtained and used to investigate polymers with large alternation such as polysilane.