Considerable theoretical and experimental interest has centered on the origin of exceptional second- [χ(2)] and third- [χ(3)] order nonlinear optical responses of π-electron excitations in organic and polymeric structures and the potential applications of these responses in nonlinear optical devices,1 We report initial χ(3) measurements by third-harmonic generation (THG) for the new class of divinyldiacetylene (DVDA) conjugated polymers that form by novel liquid crystal (LC) polymerization. X-ray structure studies showed that DVDA monomers crystallize in mesogenic structures with their long molecular axes aligned parallel in chains and sheets characteristic of precursor nematic and smectic LC phases (Fig. MCC4-1). With increased temperature, DVDA monomer crystals undergo a reversible LC phase transition and then polymerize irreversibly in the LC phase to form high-optical-quality polymer films exhibiting transparency from the near-IR region at 3 μm to the visible red region at 0.6 μm, where there is a large, sharp onset of π-electron excitations of the conjugated polymers. The THG measurements were performed using wedge Maker fringe techniques in air and vacuum. The lowest χ(3) value observed for these new LC polymer films is 2 orders of magnitude larger than the reference values for quartz and glass.

© 1984 Optical Society of America

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