Correlation between photoinduced absorption and large off-resonant nonlinear refractive index of polydiacetylene

We have calculated the off-resonant nonlinear refractive indices of PTS and TCDU polydiacetylenes using photoinduced absorption data and applying the Kramers–Kronig transformation. The results are in good agreement with the recently published experimental measurements. This is the first time that a correlation between photoinduced absorption and the off-resonant nonlinear refractive index has been established for polydiacetylenes. The calculated values are: n2∼1.3×10−5 cm2/MW for PTS, and ∼2.2×10−6 cm2/MW for TCDU at 1.06-μm wavelength. The sign of n2 is positive at this wavelength.