Adjusting the third-order nonlinear optical properties of a conjugated polymer film

We demonstrate the ability to adjust and control the magnitude of the third-order nonlinear response of a conjugated polymer, the processable polydiacetylene poly(4BCMU), through macroscopic polymer processing techniques. The demonstration of control over chi((3)) in a conjugated polymer is accomplished by using stimulated inverse Raman scattering. The control is achieved through the balance of two opposing effects introduced by processing: the enhancement in nonlinear response per chromophore unit and the misalignment of the chromophores relative to the incident linearly polarized electric field. We observe a significant enhancement of the nonlinear response in the stretch-aligned material compared to the non-aligned material, with the enhancement limited in our measurements by the extent to which the optically active polymer and supporting substrate can be elongated.