Nonlinear Characterization of Safranin O Dye for Application in Optical Limiting

The optical nonlinearity of safranin O dye in methanol solution at different concentrations and as a solid film with polymethylmethacrylate (PMMA) has been studied using cw Nd-YAG laser at 532 nm as the source of excitation. The optical responses were characterized by measuring the intensity dependent refractive index $(n_2)$ of the medium using the Z-scan technique. The open aperture Z-scan trace of the dye in solution and solid sample displayed saturable absorption. The closed aperture Z-scan trace of the dye exhibited a negative (defocusing) nonlinearity. The nonlinear refractive index was found to vary with concentration. Optical limiting characteristics of the dye at various concentrations in solution were studied. The nonlinearity appears to be of thermal origin.