ORIENTED THIN-FILMS FOR NONLINEAR OPTICS

Nonlinear optical dichroism technique is shown to be an useful tool fo r the 1D conjugated polymer chain orientation study. When done as a fu nction of rotation angle it gives the order parameters. These paramete rs can be also obtained by coupling this technique with linear dichroi sm method. The technique is illustrated by third harmonic generation o n epitaxied polydiacetylene thin films either on single-crystalline or on preoriented ultrathin films by rubbing. Whereas an almost perfect orientation is obtained in the case of epitaxy of p-DCH, poly [1,6-bis (N-carbazolyl)-2,4-hexadiyne], on KAP, potassium acid phthalate, singl e crystal, this is smaller for epitaxy on preoriented substrate. The r esults are correlated with thin film texture measurements with X-rays. A good overall agreement is seen except that X-ray data show better o rder than nonlinear optical dichroism. A possible origin of this diffe rence is shortly discussed.