Study of nonlinear optical properties of Carbon nanotubes synthesized by Nickel and Nickel-Cobalt catalysts using Z-scan technique

The nonlinear optical properties of carbon nanotubes (CNTs) have been studied by using the Z-scan technique. Experiments are performed by CW second harmonic of Nd-YAG laser at 532 nm wavelength with a power of 40 mW. The samples are synthesized by the chemical vapor deposition (CVD) method in the presence of Nickel and Nickel-Cobalt catalysts. In this work, for the first time, effect of the type of catalyst has been investigated with CNTs being a set of series single-walled and multi-walled nanotubes with different diameters. Nonlinear refractive index (n2) and nonlinear absorption coefficient (β) were measured by a closed and open aperture experimental configuration of Z-scan. The experimental results show that the two-photon absorption effect is the dominant nonlinear process in the samples. The results approve the capability of the samples to be used as an optical limiter device. The nonlinear optical refractive index and nonlinear absorption coefficient of samples are in the order of 10-6 cm2/W and 10-1 cm/W, respectively. The sign of nonlinear refractive index of the samples is negative which indicates that the sample has acted as a divergent lens.