RESONANT DEGENERATE 4-WAVE-MIXING AND SCALING LAWS FOR SATURABLE ABSORPTION IN THIN-FILMS OF CONJUGATED POLYMERS AND RHODAMINE-6G

Wavelength dispersed degenerate four wave mixing (DFWM) experiments were performed with thin films of poly(3-decylthiophene), poly(p-phene vinylene) and Rhodamine 6G. At the low energy side of the main absorption bands the resonant chi(3) (-omega; omega, omega, -omega) values scale differently with the absorption coefficient-alpha. In Rhodamine 6G, chi(3) is proportional to alpha-2 due to saturable absorption in a two level system. In the case of polymers with a conjugated one-dimensional pi-electron system a linear relationship between chi(3) and alpha is found. This is attributed to phase-space filling effects by one-dimensional excitons.