Estimation of enhancement in third-order nonlinear susceptibility induced by a sharpening absorption band

We derived an empirical relationship between |χ⁽³⁾| and absorption spectra based on a simple two-level model. We calculated third-order nonlinear susceptibility for a methanol solution of rose bengal (RB), a polydiacetylene thin film (PDA), and a GaAlAs/ GaAs multiple quantum well (MQW) using the relationship. The estimated values are of the same order as the experimental ones. We also investigated the effect of the sharpening absorption bandwidth on |χ⁽³⁾| enhancement, and found that |χ⁽³⁾| of 10⁻⁶ esu can be expected if the width of the PDA absorption band is reduced by one order of magnitude.