DISPERSION OF CUBIC SUSCEPTIBILITY OF THIN-FILMS OF PSEUDOISOCYANINE J-AGGREGATES AS MEASURED BY LONGITUDINAL SCANNING

The method of longitudinal scanning is used for measuring the dispersi on of the nonlinear index of refraction and nonlinear absorption coeff icient of thin films of pseudoisocyanine J-aggregates. The measured qu antities were used for calculations of the imaginary and real parts of the cubic susceptibility. Numerical calculations of the dispersion of the real part of the nonlinear susceptibility are carried out based o n the Kramers-Kronig relations and the data obtained for the imaginary part. It is shown that the imaginary part of the cubic susceptibility is determined by the transient bleaching of the exciton absorption pe ak of J-aggregates. The observed features of the cubic susceptibility dispersion are explained within the framework of the four-level diagra m of the exciton transitions in J-aggregates.