Ultrafast third-order optical nonlinearity of polybenzonitriles

The second-order hyperpolarizabilities gamma 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 gamma as large as 4.8 x 10(-32) esu has been obtained for PHBN with only eight conjugated bonds. Compared with structurally similar materials, these polynitriles have larger gamma at the same conjugation length. The dependence of gamma on the substitution groups and the conjugation length was also studied. (C) 2000 Published by Elsevier Science B.V.