Ultrafast third-order optical nonlinearity of polybenzonitriles

The second-order hyperpolarizabilities γ of two novel substituted polynitriles: poly(p-methyl-benzonitrile) and poly(p-hydroxylbenzonitrile) (PHBN) were measured by using femtosecond time-resolved optical Kerr effect at 820 nm. The results show that these polynitriles have large non-resonant third-order optical non-linearities. Non-resonant γ as large as 4.8×10−32 esu has been obtained for PHBN with only eight conjugated bonds. Compared with structurally similar materials, these polynitriles have larger γ at the same conjugation length. The dependence of γ on the substitution groups and the conjugation length was also studied.