Second-harmonic generation in vinylidene fluoride-trifluoroethylene copolymers doped with donor-acceptor molecules

The temperature dependence of the second-harmonic generation in a vinylidene fluoride-trifluoroethylene ferroelectric copolymer doped with 5 wt % of a noncentrosymmetric 4-anilino-4′-nitroazobenzene chromophore is analyzed. The second-order susceptibility χ(2) in the ferroelectric phase of these copolymers appears to be twice as high as in the poly(methyl methacrylate) with the same chromophore content. The effect is attributed to the presence in ferroelectrics of a local electric field associated with the spontaneous polarization. The intensity of the second-harmonic generation in both ferroelectric and paraelectric phases correlates with the variation of the surface potential.