Electroabsorption spectra have been measured for nonoriented trans-cis
blend films of highly ordered 'soluble' polyacetylene in the spectral
range 1.3 to 2.5 eV for different temperature and probe polarization.
The electroabsorption spectra follow the second derivative of the abs
orption spectrum except the region below the absorption edge of the tr
ans isomer. The observed electroabsorption for the cis isomer is consi
derably weaker than that for the trans isomer. The non-resonant nonlin
ear susceptibility chi((3))(omega;omega,0,0) of the 'soluble' trans-(C
H)(x) has been estimated to be similar to 2x10(-11) esu.