The absorption spectra of methyl red (MR) dissolved in methanol, ethanol, dimethyl sulfoxide, and hexane were measured. It was found that the peaks of the absorption spectra of MR solutions shifted toward shorter wavelengths with increasing solvent polarity. Using the Z-scan method, the nonlinear optical properties of the four kinds of MR solutions were determined at wavelength 441.6 nm. The effective nonlinear indexes of refraction (n2) of MR solutions increased with the increasing thermo-optical coefficients of the solvents. In addition, the optical limiting effects of the MR solutions were investigated at 441.6 and 535 nm, and the results indicate that they possessed strong optical limiting effects.
The nonlinear optical properties of ethyl red (ER) doped PMMA film are measured, and the effective indexes of refraction n<sub>2</sub> of the film at the three wavelengths are -1.08×10<sup>-9</sup>, -2.28×10<sup>-9</sup> and -1.35×10<sup>-10</sup>m<sup>2</sup>W<sup>-1</sup> respectively. It indicates that ER sample has a larger optical nonlinearity compared with other optical materials. The nonlinear absorption of ER film at the three wavelengths is measured respectively. The self-diffraction of the film at 441.6nm and at 535nm is investigated respectively, and the results indicate it possesses high quality of optical limiting. The lasers of 441.6nm and 535nm can all induce thermal self-defocusing effects in the film.
The absorption spectra of Congo red (CR) in aqueous solution and PVA film are measured, respectively. With the Z-scan method, the nonlinear optical properties of CR are investigated, and experimental data on the nonlinear refractive index and the change of refractive index are obtained. As a result, the intensity dependent index n<sub>2</sub> of CR has been determined to be in the range from 10<sup>-10</sup> to 10<sup>-9</sup> m<sup>2</sup>/W. The nonlinear absorption of CR aqueous film and CR-doped PVA film for three wavelengths is measured respectively. Under the condition of that the two samples are irradiated by 443nm or 535nm, the characteristics of absorption as function of the power of 633nm are determined. Finally, the experimental results are analyzed.