Study of nonlinear optical properties of organic material utilizing two-color Z-scan

The theory of two-color Z-scan was studied. The expression of the normalized on-axis transmittance in the far field was derived with some simplifications, and the influences of the wavelength and beam waist radius of the pump and probe beams on the measurement sensitivity were discussed. Utilizing an Ar⁺ laser with the wavelength of 514.5 nm as pump beam and a He-Ne laser with the wavelength of 632.8 nm as probe beam, a two-color Z-scan experiment was performed in organic solvents of C60 and 4-BCMU which has different absorption coefficients at 514.5 nm, and their thermal-induced non-degenerate nonlinear refractive index n2 were measured to be -3.46×10^-5 esu and -4.06×10^-5esu, respectively. Some phenomena observed in this experiment were explained.