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Detailed investigations of the quadratic nonlinear response of a series of new polyimides with covalently attached chromophore DR13 are performed by the Maker fringes method in the range of fundamental wavelength from 850 to 1450 nm. Polymer films with thickness of 100–400 nm were spin-coated on glass substrates and corona poled. For these materials, the maximum values of the second harmonic generation coefficients d33 are 80-120 pm/V. A red shift of the nonlinear response dispersion with respect to the linear absorption spectrum was observed for the DR13 chromophore. The temperature dependences of linear absorption and nonlinear coefficients d33 for studied structures are observed. It was found that the temperature changes of the absorption spectra lead to appreciable contribution to the value of the nonlinear coefficient d33. The demonstrated high temperature stability (up to 120 °C) of chromophore-containing polyimide thin films makes it possible to eliminate the degradation of their nonlinear optical properties in the future applications of such structures. [ABSTRACT FROM AUTHOR]

A comparative study of the dispersion of nonlinear absorption in thin films of molecular J- and H-aggregates of polymethine dyes was performed with the use of the Z-scan (Z-scan technique) over the range 625–825 nm under conditions close to resonance absorption at nanosecond duration of excitation. The measurements were made on film samples of J- and H-aggregates prepared by spin-coating and having identical absorption spectra. The H- and J-aggregates were formed by the synthetic thioflavylium DT-3 and benzothiazole BTC18H dyes, respectively. It was found that the samples of different types of aggregates exhibit nonlinear susceptibility of the same order of magnitude with allowance for the width of exciton absorption peaks. [ABSTRACT FROM AUTHOR]