The Optical Nonlinearity of Au and Ag Nanoparticle Prepared by the Γ-Radiation Method

Abstract

Problem statement: The third order nonlinear optical properties of met al nanoparticles have been of interest in physical chemistry, medica l diagnostics and optical devices. Gold colloidal nanoparticles are responsible for the brilliant red s seen in stained glass windows and silver particle s are typically yellow. The purpose of the study was to d etermine the nonlinear refraction and absorption coefficient of the Au and Ag nanoparticles in PVP s olution. Approach: The samples were prepared by γ-radiation method and the nonlinear optical propert ies of the composites were investigated using a single beam Z-scan technique with a beam power of 40 mW and operated at wavelength of 532 nm. The measurements were carried out for both Open and closed aperture Z-scan arrangements. Results: For both Au/PVP and Ag/PVP samples the results exhibited reverse saturable absorption. The closed aperture Z-scan of the nano-fluid samples re vealed self-defocusing effect while the open aperture Z-scan of the samples show a reversible sa turable absorption. Conclusion: The Z-scan measurement showed that silver and gold nano-fluid prepared by gamma radiation exhibited large thermal nonlinear refractive index n 2 as -8.78◊10 -7 and -2.478◊10 -6 cm 2 /W, respectively. We have also investigated nonlinear absorption of these samples and we found a large value of nonlinear absorption for Ag nanoparticle and a weak absorption for Au na noparticle. In conclusion, the experimental result shows a good nonlinear refractive index at low lase r power in which encouraging for possible applications in nonlinear optical devices.