Caracterização da não linearidade óptica de nanotubos de carbono de única parede mediante a técnica de Varredura Z com laser de alta taxa de repetição

Abstract

In this work, we have made the study and characterization of nonlinear third-order optical properties of samples containing single-walled carbon nanotubes. The Z-scan technique with high repetition rate laser was used. This technique was employed using as light source a linearly polarized Ti:Sapphire laser, emitting pulses of 140 fs duration and at 80 MHz repetition rate. The laser was tuned to different wavelengths, ranging of 700 to 850 nm. The samples exposure were controlled by a chopper with a frequency of 5 Hz. The transmitted light was measured by a photodetector as a function of sample position, and the data were sent and stored on a computer, through an elaborate program in LabView. Through the measurements made, it was possible to determine the value of the nonlinear refractive index n2 of the samples studied for each wavelength. Both samples showed an intense nonlinearity of negative electronic source (n2 < 0). Observing the change in nonlinear refractive index n2 for each laser wavelength, it was observed that these curves follow the linear absorption spectrum for the nanotubes samples, namely, in the region of the absorption bands. Both samples showed the same behavior. It was also possible to determine the value of the nonlinear absorption coefficient α2 for one of the samples. This sample showed minimal transmittance curves (α2 > 0), indicative of a process of absorption of several photons. Finally, it was observed that all nonlinearity presented was due to the presence of single-wall carbon nanotubes in the samples.