Solvatochromism and third-order nonlinear optical responses of Azo dye

Abstract Third-order nonlinear optical (NLO) properties of acid black 32 (AB 32); an azo dye is studied by sensitive Z‒scan method. The dye is dissolved into various solvents like methanol, acetone, ethanol, water, DMF and DMSO at 0.01 mM concentration. The diode laser with operating wavelength of 650 nm is used to study the third-order NLO characteristics of AB 32 dye. The effect of solvent spectral characteristics on linear absorption coefficient and third-order NLO features of AB 32 dye is studied and multi-parameter scale known as Kamlet-About-Taft is used to analyze the solvent characteristics on solute molecule. The nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of the dye sample is respectively measured to be the order of 10− 7cm2/W and 10− 2 cm/W. The title sample shows both positive and negative nonlinear absorption (NLA) coefficient owing to the phenomenon of saturable and reverse saturable absorption (RSA), as well as negative nonlinear index of refraction as a result of self-defocusing. The order of third-order NLO susceptibility (χ(3)) of AB 32 dye in different polar solvents is measured to be 10─6 esu. The obtained results propose that AB 32 dye is a suitable material for future NLO applications.