Direct evidence of the failure of electric-dipole approximation in second-harmonic generation from a chiral polymer film

Abstract
Second-harmonic generation from Langmuir–Blodgett films of a polythiophene is strongly influenced by the chirality of the polymer. The polarization dependence of the process cannot be explained in the electric-dipole approximation. Evidence of contributions beyond electric dipoles is obtained directly from individual second-harmonic signals.