Z-scan measurements of the concentration-dependent optical nonlinearity of methyl blue using 800 nm femtosecond laser

Abstract

The third-order nonlinear optical properties for aqueous solution of methyl blue are explored by the Z-scan method with 800 nm fs radiation. The magnitudes and signs of the nonlinear refractive index n2, the nonlinear absorption coefficient β, and the third-order nonlinear optical susceptibility χ(3) are determined at four different concentrations. The β and n2 values are found to be in the order of 10−13 m/W and 10−20 m2/W, respectively. All the calculated nonlinear optical parameters are linearly proportional to the sample concentration in the studied range. The open aperture Z-scan of methyl blue exhibits reverse saturable absorption, and the closed aperture transmittance reveals the self-defocusing effect and the negative refraction nonlinearity. Our results indicate that methyl blue may be a promising candidate for photonic applications.