Plasmon-enhanced optical nonlinearity in pyramidal silver nanocrystals

This study investigates the coherent optical nonlinearity of two sets of anisotropic silver nanocrystals (NCs) showing plasmon peaks at 530 and 610 nm (hence named Ag-530 and Ag-610 NCs, respectively). The nonlinear optical (NLO) properties of Ag-530 and Ag-610 NCs are compared with spherical silver NCs exhibiting plasmon peak at 420 nm (hence called Ag-420 NCs). Resonant excitation induces significant one-photon absorption (1PA) saturation for all NCs, with Ag-610 NCs displaying exceptional transparency. Off-resonant excitation reveals efficient two-photon (2PA), three-photon (3PA), and saturable (SA) absorption in Ag-610 NCs. In the 3PA regime, the effective nonlinear absorption coefficient of Ag-610 NCs is 221% and 340% that of Ag-420 and Ag-530 NCs, respectively, at a laser intensity of 40 GW/cm². The impressive absorption figures of merit of Ag-610 NCs make it the ultimate contender for high-performance 2PA and 3PA applications.