Nonlinear Refraction and Absorption of Ag-29 Nanoclusters: Evidence for Two-Photon Absorption Saturation

We report the nonlinear absorption and refraction of Ag-29 nanocluster aqueous suspensions using the open and closed aperture Z-scan method at 532 nm. The stoichiometry of the atomically precise silver nanoclusters has been determined by mass spectrometry, and their formula is Ag(29)DHLA(12) where the ligand is dihydrolipoic acid (DHLA). Using different concentration of nanoclusters, we observe beyond the expected linear absorption saturation and nonlinear absorption a clear saturation of the nonlinear absorption, a feature so far not described for nanoclusters. The nonlinear refraction is also determined and exhibits a regular behavior with a negative n(2) value. A figure of merit is discussed in view of potential applications.