Degenerate four-wave mixing in azo-dye-doped polymer films

We report experimental results for the third-order nonlinear properties of thin polymer films doped with azo dyes, which have long-lived triplet states and can undergo reversible photochromic reactions. Cast films of Disperse Red 1 and Methyl Red in polystyrene and polymethyl methacrylate were investigated by degenerate four-wave mixing with a low-power cw mode-locked laser. Polarization properties and the time dependence of the laser-induced gratings were investigated, and results were compared with those obtained for liquid solutions of the dye in the respective monomers. A phase-conjugate reflectivity of 1% was observed for Disperse Red 1 in polystyrene, with no long-term degradation under laser irradiation.