Femtosecond measurement of the third order nonlinear optical coefficients of CuPc (copper phthalocyanine), CoPc (cobalt phthalocyanine) and ZnPc (zinc phthalocyanine) thin films using Z-scan measurement method

The Z-scan measurement method possessing the simplicity of the experiment set-up as well as the simplicity of the interpretation separately determines the nonlinear changes in index and absorption and has the high sensitivity to all nonlinear optical mechanisms. Thus we performed the experiment varying a repetition rate at 82 MHz, 4 MHz, 800 kHz and 400kHz with a pulse selector in the laser system. We found that the larger the repetition rate was, the more dominant the thermal nonlinearity was in both the nonlinear changes in index and absorption. At the 400 kHz and 800 kHz repetition rate where the samples didn´t show thermal nonlinearity, we compared the experiment results with the theory derived from GD (Gaussian decomposition) method. At the 4 MHz and 82 MHz repetition rate where the thermal nonlinearity was dominant we explain the experiment results both qualitatively and quantitatively. The samples were irradiated by Ti-sapphire femtosecond laser with pulse widths of FWHM 100-200 fs. The samples employed for the measurement were CuPc (copper phthalocyanine), CoPc (cobalt phthalocyanine) and ZnPc (zinc phthalocyanine), fabricated in a thin film by a vacuum evaporation.