Large nonlinear absorption and refraction coefficients of carbon nanotubes estimated from femtosecond z-scan measurements

Abstract

Nonlinear transmission of 80 and 140 femtosecond pulsed light with 0.79 μm wavelength through single walled carbon nanotubes suspended in water containing sodium dodecyl sulfate is studied. Pulse-width independent saturation absorption and negative cubic nonlinearity are observed, respectively, in open and closed aperture z-scan experiments. The theoretical expressions derived to analyze the z-dependent transmission in the saturable limit require two photon absorption coefficient β₀~1.4 cm/MW and a nonlinear index γ~−5.5×10⁻¹¹ cm²/W to fit the data.