Azo doped polymer thin films for active and passive optical power limiting applications

Abstract

Two novel optical power limiters, 2-[ethyl-(4-phenylazo-phenyl)-amino]-ethanol (E4PA) and 2-[ethyl-(4-trifluoromethyl-phenylazo-phenyl)-amino]-ethanol (E4TPA) were synthesized using a diazotization reaction. The purified azo material was made into thin films in a poly(methyl methacrylate) matrix using a gravity settling technique. The electronic nonlinearities of these films were investigated using an open aperture Z-scan technique in the fs excitation regime, resulting in nonlinear absorption due to a two-photon absorption (2PA) process. The 2PA coefficient for these films is of the order 10⁻¹² m W⁻¹ and the limiting threshold values are 1.1 J cm⁻² each. A non-degenerate pump probe set-up was employed with CW lasers to study the nonlinear behaviour arising from photo-induced anisotropy and excited-state absorption. The present study shows that these azo thin films are potential candidates for active and passive optical power limiting applications.