New polymers for second-order nonlinear optics

Approaches to the development of polymeric nonlinear optical materials are discussed, and recent results are reported. Selected chromophores with high quadratic molecular optical nonlinearities have been covalently linked by several synthetic procedures to produce robust glassy film-forming chloromethylated or hydroxylated polystyrenes. By this procedure, it is possible to achieve polymeric materials with high chromophore densities, good optical transparency, and good chemical stability. Coating of these polymers onto conductive glass, followed by electric-field poling near the glass transition temperature, yields films with high second-harmonic-generation (SHG) efficiencies that exhibit long-term temporal stability. As an example, films of poly(p-hyroxystyrene) functionalized with N-(4-nitrophenyl)-L-prolinol exhibit SHG coefficients d₃₃ as high as 18 × 10^-9 esu at 1.06 μm. Lifetimes of many months have been observed. Results indicate that the free volume and thermally activated backbone motion in polymer glasses are two important factors that determine the rate of chromophore reorientation.