Optical Saturable Absorption in Gold Nanoparticles

In this work, we present the experimental study of the nonlinear absorption of gold nanospheres and nanorods in aqueous suspension, using picosecond white-light supercontinuum open-aperture Z-scan. We demonstrate a saturable absorption effect in all particle suspensions at low-pulse energy. In the high-pulse energy regime, the apparent reverse-saturable absorption, observed in gold nanorods, was determined to be induced by photodegradation. Using the Lorentzian deconvolution method for the absorption spectra, we explain the variations on nonlinear optical effects and prove that saturable absorption only occurs within the plasmonic bands.