Anisotropy of the linear and third-order nonlinear optical properties of a stretch-oriented polymer film of poly-[2,5-dimethoxy paraphenylenevinylene]

Large linear refractive index birefringence, strong dichroic behavior, and highly anisotropic χ(3) have been observed for a uniaxially oriented poly (2, 5-dimethoxy paraphenylene vinylene) film. A subpicosecond time-resolved degenerate four-wave mixing study reveals an unusual behavior. Along the draw direction χ(3) is complex with a negative real part and has a response time that is longer than the optical pulse resolution. In contrast, χ(3) along the transverse direction is largely real and positive. Its response time is much faster, and is limited by the laser pulse width of ∼400 fs.