Mechanisms for fabrications and nonlinear optical properties of Pd and Pt nanoparticles by femtosecond laser

Pd and Pt nanoparticles (NPs) are fabricated in solution through the photodecomposition of PdCl2 and H2PtCl6 by femtosecond laser, respectively. The fabrication mechanisms are discussed. The nonlinear optical properties of Pd and Pt NPs are investigated by using Z-scan technique with femtosecond laser at 800 nm. With the increase of irradiation intensity, Pd NPs exhibit positive nonlinear absorption (PNA) throughout, whereas Pt NPs experience a transformation from saturable absorption (SA) to PNA. The PNA of Pd NPs is ascertained to the two-photon absorption (TPA) between d band and conduction band. The SA of Pt NPs is attributed to the intraband absorption in conduction band and the mono-photon absorption between d band and conduction band, and the PNA is attributed to TPA between d band and conduction band along with the free carrier absorption. We show that the Pd colloid satisfies the requirements for optical switching.