Optical characterization of Methylene blue over the whole visible range

In the present study, the linear optical properties and the nonlinear refraction of the Methylene blue (MB) dye have been studied over almost the whole visible range in two polar solvents. The linear characterization includes investigating the influence of solvent molecules on the absorption of the solute. The nonlinearity of the dye solutions is examined by the z-scan technique with CW exciting lasers that having four different wavelengths (405, 473, 532, and 650 nm). The results of the study show that the MB dye has maximum nonlinearity at wavelength 650 nm in both solvents (-0.612 and -0.302 cm2/MW in ethanol and water respectively). At the other wavelengths the dye shows noticeable nonlinear refraction with index of refraction (n2) ranges almost within the same order of magnitude. The use of water leads to significantly quench the nonlinearity of the dye. Adding NaCl to the aqueous solution of the dye affects a certain linear transition of the dye and slightly changes its nonlinear refraction. The results of the present study indicate that MB dye can be a good candidate for many optoelectronic devices.