Large resonant third-order optical nonlinearity of thin film containing J-like aggregates of a bis [4-( N -dibutylamino)phenyl]squarylium dye

The third-order optical nonlinearity and response of thin film containing J-like aggregates of a bis [4-( N -dibutylamino)phenyl]squarylium dye were measured by degenerate four-wave mixing (DFWM) technique under resonant conditions. The temporal profile of DFWM signal was obtained with a time resolution of 0·3 ps (FWHM), and was found to consist of at least two components, i.e. the coherent instantaneous nonlinear response (electronic response) and the slow response due to the excited state population grating. The effective χ (3) value of thin squarylium dye film was evaluated to be as high as 1·1 × 10 − 7 esu, and the figure of merit of third-order nonlinearity F ( F = χ (3) / α ), was calculated to be about 2·1 × 10 − 13 esu cm.