Improved optical nonlinearity of poled stilbene doped polymer films

The optical properties of corona poled 4'-N,N-dimethylamino-nitrostilbene (DANS) and a newly synthesized alpha'-cyano-4'-nitro-4-N,N-dimethylaminostilbene (CNDS) doped poly(methyl methacrylate) (PMMA) film were investigated with in situ second-harmonic generation (SHG) measurement and absorption measurement. Optimum corona poling temperatures of these polymer films were found to be lower than glass transition temperatures of the materials, most probably due to the dramatic increased conductivity of the films and phase separation. Under the optimum: corona poling condition, the alignment ordering of CNDS was lower than that of DANS from the absorbance before and after: corona poling. But the second-order nonlinear susceptibility X-(2) of CNDS/PMMA is improved compared with that of DANS/PMMA. The molecular second-order polarizability beta of the CNDS/PMMA was estimated to be about 140 x 10(-30) esu from the measured absorbance and X-(2) The relaxation of SHG intensity of CNDS/PMMA was slower than that of DANS/PMMA. This showed that CNDS is a kind of better dopant than DANS as second-order nonlinear-optical material. (C) 1999 Elsevier Science B.V.