WAVELENGTH-DEPENDENT NONLINEAR-OPTICAL PROPERTIES OF PSEUDOISOCYANINEJ-AGGREGATES

Degenerate four wave mixing of tunable picosecond pulses were carried out in pseudoisocyanine J-aggregates near resonance. The conversion ef ficiency was very high even at very low intensities of interacting bea ms. The power of intensity dependence of the converted signal was show n to change with wavelength within the J-band. The range of the power dependence was from approximate to 1.5 (in the center of the J-band) t o three (at the wings of the J-band). This effect is related to the sa turation of population density, to singlet-singlet annihilation and se condary processes of local vibrational excitation or heating. The diff erent extent of saturation and heating causes the deviation from third order power dependence on intensity within the J-band. The dependence of the timing of the three pulses supports the interpretation of such a behaviour by an annihilation and secondary processes. The cubic sus ceptibility was estimated at the wings of the J-band to a value of 10( -8) esu.