Abstract

This paper presents experimental measurements and theoretical analysis of the third-order optical susceptibility measurements by degenerate four-wave mixing in several classes of polymeric film which have conjugated π-electron structure. A high X⁽³⁾ value derived from the π- electron conjugation effect is observed, and a subpicosecond response is confirmed. The first group is a conjugated aromatic heterocyclic polymer, poly-p-phenylenebenzobisthiazole (PBT), which has very high mechanical strength due to its rigid rod conformation as weil as environmental stability and a high laser damage threshold. The X⁽³⁾ measurement in a 33-µm thick biaxial film of PBT yields a value ~1 order of magnitude larger than than for CS₂. The measurements at two wavelengths suggest that they are nonresonant X⁽³⁾ values. The measured anisotropy of X⁽³⁾ as a function of angular orientation at two different sets of laser polarization is explained by using the tensor properties of X⁽³⁾ in an anisotropic medium. The angular dependence and waveiength depen- dence for the degenerate four-wave mixing slgnal for the PBT film are shown in Fig. 1.

© 1986 Optical Society of America