Complex third-order phase conjugation nonlinearity of polymeric thin films

Abstract
We describe a simple method for measuring magnitude and argument of degenerate four-wave-mixing nonlinearities in polymer thin films. It is based on an analysis of phase conjugation response of films interfering with their glass substrate. In evaporated polycrystalline polydiacetylene blue layers, picosecond two-photon resonant nonlinearity is a function of pump intensity. It increases and undergoes a 30° argument variation between 0.2 and 1 GW/cm2.