“Third-Order Non-Linear Optical Interactions in Thin Films of Organic Polymers Investigated by Picosecond and Subpicosecond Degenerative Four Wave Mixing"

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 films which have conjugated π-electron structure. A high χ(3) value derived from the π-electron conjugation effect is observed and a subpicosecond response is confirmed. The first group is a conjugated aromatic hetrocyclic polymer, poly-p-phenylenebenzobisthiozole (PBT) which has a very high mechanical strength due to its rigid rod conformation as well as environmental stability and a high laser damage threshold. The χ(3) measurement in a 33 μM thick biaxial film of PBT yields a value about an order of magnitude larger than that for CS2. The measurements at two wave lenghts suggests that they are non­resonant χ(3) values. The measured anisotropy of χ(3) as a function of angular orientation at two different sets of laser polarization is explained by using the tensor properties of χ(3) in on anisotropic medium.