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.