The third- and fifth-order nonlinear refraction in the single- and double-sided TMAF/PSS electrostatic self-assembly films

The nonlinear refraction in the single- and double-sided 40-bilayer TMAF/PSS electrostatic self-assembly films were measured by closed-aperture Z-scan technique with picosecond laser pulses (with duration of 40 ps at 532 nm). The materials contain a positively charged material trifluoroacetic acid (TFA) salt of amino-substitute methanofullerene derivative monoadduct fullerene (TMAF) and a negatively charged material ploy (sodium 4-styrenesulfon ate) (PSS). The experimental results show that under the conditions of the peak intensity I₀ = 7.0 GW/cm², both the single- and double-sided films demonstrate third- and fifth-order non-linearities, and the fifth-order non-linearity has greater contribution to the nonlinear refraction than the third-order nonlinearity. The theoretical fittings also prove that the nonlinear refraction coefficients both γ and η are almost the same for the same materials no matter what the measurements are from the single- or the double-sided films.