Nonlinear absorption of some thiazine, xanthene, and carbocyanine dyes

The saturated and two-photon absorption of various classes of heterocyclic dyes [thiazine (thionine), xanthene (erythrosine), and carbocyanine (3,3′-di-(γ-sulfopropyl)-4,4′,5,5′-dibenzo-9-ethylthiacarbocyaninebetaine pyridinium salt, DEC)] possessing optical absorption in the 500-680 nm range were measured at the wavelengths of 1064 and 532 nm using nanosecond (10 ns) and picosecond (40 ps) pulses and z-scan technique. It was shown that reverse saturated absorption unlikely plays important role in those dyes. We defined the two-photon absorption coefficients of thionine and erythrosine at 1064 nm using 40 ps pulses (0.8 × 10−11 and 1.0 × 10−11 cm W−1 respectively). The concurrence of saturated absorption and two-photon absorption was analyzed in the case of thionine and erythrosine using various models. It was suggested that dimerization of those dyes significantly suppresses the nonlinear optical response in the case of both 10 ns and 40 ps pulses of 532 nm radiation. At the same time it was found that, in the case of 532 nm pulses, the monomers of thionine participate in the processes of saturated absorption and two-photon absorption, while J-aggregates of DEC show predominantly two-photon absorption.