The dynamics and the sub-picosecond resonant third-order nonlinearity of azobenzene-doped polymer films are investigated by means of transient degenerate four-wave mixing andz-scan techniques. The third-order susceptibility&khgr;(3)and the dephasing timeT2are measured to be(6.3±0.6)×10−12 esuand(1.0±0.1)×10−12 psec,respectively. The creation of a new intermediate state related to a conformational deformation mechanism is supported by experimental observations. ©1997 American Institute of Physics.