A Novel Study of the Nonlinear Optical Properties of Aniline Blue by Changing the Solution PH

Abstract

Organic laser dye Aniline Blue (AB) has linear and nonlinear  optical properties. In this study, the cationic form of  AB dye solutions was prepared by the adjusted over the range (pH=1) once by adding HCl, another one by adding CH₃COOH to dye solutions . An  NaOH, one more time NH₃ to dye solutions adjustment over the range (pH=10)  to generate the  zwitterionic  form, the acids and bases were added to dye solution at concentration 1×10^-4 M with an methanol solvent. The absorbance intensity range shifts toward the longer wavelengths (red shift) at pH=1, while the absorbance intensity shifts towards the shorter wavelengths (blue shift) at pH=10. Organic dye absorption spectra have a wavelength range of (550-604) nm. Negative nonlinear refractive index of the AB dye in methanol and its different solutions pH  measured by the z- scan was employed using continuous wave (CW) diode pump solid state blue laser at wavelength (457 nm) and (112 mW) power. In a closed aperture z-scan, the findings indicate a change in the effect from self-focusing to self-defocusing. (and in open aperture z-scan, the effect changes from two photon absorption to saturabl  absorption), When the weak base was added to the dye solution.