By applying the Maxwell Garnett model to gold nanoparticles in water we deduce a value of Im xi (3) 5 1.1 3 1027 esu for the imaginary part of the cubic susceptibility for gold corresponding to a Fermi smearing mechanism. We also demonstrate a sign reversal in the nonlinear absorption for gold particles in 1, 18, 3, 3, 38, 38-hexamethylindotricarbocyanine iodide. Although the imaginary part of ...
