Synthesis, Characterization And Nonlinear Optical Properties Of Laser-induced Au Colloidal Nanoparticles

Gold (Au) colloidal nanoparticles (NPs) have been synthesized by direct irradiation of gold precursor (HAuCl4) solution in polyvinyl alcohol (PVA) matrix using nanosecond laser pulses at different irradiation fluencies and exposure times. Appearance of wine and dark wine colors indicated the formation of Au NPs. Transmission electron microscope (TEM) images exhibited spherical shaped particles and X-ray Diffraction (XRD) pattern confirms polycrystalline nature of Au NPs with cubic structure. Au NPs displayed negative nonlinearity and exhibited a shift from saturable absorption (SA) at lower intensities to reverse saturable absorption (RSA) accompanied by nonlinear scattering at higher excitation intensities in nanosecond regime at 532 nm. Two-photon absorption (TPA) is attributed to be responsible for the RSA behavior.