CONJUGATED POLYMERS WITH DEGENERATE GROUND-STATE - THE ROUTE TO HIGH-PERFORMANCE 3RD-ORDER NONLINEAR-OPTICAL RESPONSE

Third harmonic generation (THG) measurements on cis- and trans-polyace tylene demonstrate a symmetry specific mechanism favouring the degener ate ground state: the third-order susceptibility, chi(3)(-3omega;omega ,omega), is an order of magnitude larger in trans-(CH)x than in cis-(C H)x over the entire spectral range, even comparing the respective thre e-photon resonance maxima. Reduced disorder in high quality oriented t rans-(CH)x increases chi(3)(3omega) by more than an order of magnitude to values greater-than-or-equal-to 10(-8)-10(-7) esu for HBARomega wi thin the energy gap. The THG data are consistent with theory which pre dicts a dominant contribution to chi(3)(3omega) from neutral soliton p air intermediate states with Ag symmetry.