Solvent effects and self-assembled aggregation modulate nonlinear optical effects in indocyanine green-like dyes

The effects of various solvents and self-assembled aggregation on the third-order nonlinear optical properties of indocyanine green (ICG) and new indocyanine green (IR 820) dyes were examined using femtosecond Z-scan technique. The nonlinear absorption properties of identical dye samples in various solvents and those of the two dye samples in the same solvent were compared. In addition, differences in the nonlinear absorption properties of self-assembled H aggregates and monomers when dissolved in water are discussed. The comparison analysis results indicate that the samples exhibit significant saturable absorption phenomena and large modulation depths at various excitation light intensities, highlighting their significant potential for use as saturable absorbers in pulsed lasers. Moreover, the third-order nonlinear saturable absorption behavior can be modulated by the self-assembled aggregation of the dyes and solvents. This investigation focused on the light–matter interactions of near-infrared organic dyes, and the findings presented in this report demonstrate the potential applicability of the dyes in optoelectronics, optical modulation, and photonics.