Nonlinear optical studies of bromothymol blue in liquid and solid media

The third-order nonlinear optical properties are used in high speed telecommunications, optical limiters and optical computers. The purpose of the study is to determine the third-order nonlinear characteristics of bromothymol blue dye in both polymer and liquid mixtures. The samples are prepared by dissolving dye of different concentrations in methanol and ethanol and thin film was prepared by bulk polymerization technique. The spectral characteristics of the dye are studied by recording the absorption and fluorescence spectra of the dye doped in poly(methylmethacrylate) modified with additives ethanol and methanol and the dye in MMA with additives (liquid mixture). The spectral results of the dye doped polymer rod are compared with dye in liquid mixture. The nonlinear measurements of the dye in liquid and polymer medium were performed using CW Nd:YAG laser of wavelength 532 nm by employing Z-scan technique. The closed Z-scan of the samples exhibited a negative nonlinear refractive index, which is larger in magnitude in solid film compared to that in solution. The open Z-scan in solution and solid samples displayed reversible saturable absorption.