The third-order nonlinear optical properties of novel styryl dyes

The third-order nonlinear optical properties of two novel styryl dyes, namely, 1,3-diethyl-5-(4-methoxybenzylidene)-2-thioxodihydropyrimidine-4,6(1H,5H)-dione and 5-(3,4-dimethoxybenzylidene)-1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione were studied using the Z-scan technique employing 7 ns laser pulses at 532 nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of effective third-order susceptibility and coupling factor were determined. The optical power limiting behavior of the colorants was ascribed to two-photon absorption phenomenon. Nonlinear absorption cross-section increased with increase in π electron density and the effective two-photon absorption cross-section was two orders of magnitude larger than those of commercially available azo compounds. The results suggest that these colorants offer promise as nonlinear optical materials for device applications.