Abstract
From third harmonic generation measurements on unoriented thin films and with excitation at 1.064 µm we have determined a third order nonlinear susceptibility χ(3) (-3ω; ω, ω, ω) of 7.5 ×10-11 esu for poly(p-phenylene vinylene) [PPV]. In addition, the effect of increasing π-electron conjugation has been investigated for samples at different stages in the thermal conversion from saturated precursor to fully conjugated polymer. χ(3) increases in magnitude with increasing conversion as is expected for a nonlinearity originating in the conjugated π-electron system.