Third-order optical nonlinearity studies of bilayer Au/Ag metallic films

This paper presents nonlinear optical studies of bilayer metallic films of gold (Au) and silver (Ag) on glass substrate prepared using electron beam evaporation. The preparation of Au and Ag nanoparticles (NPs) on the substrate involved the use of electron beam deposition, then thermal annealing at 600 degrees C and 270 degrees C, respectively, to produce a randomly distributed layer of Au and a layer of Ag NPs. Observation of field-effect scanning electron microscope images indicated the size of the NPs. Details of the optical properties related to peak absorption of surface plasmon resonance of the nanoparticle were revealed by use of UV-Vis spectroscopy. The Z-scan technique was used to measure the nonlinear absorption and nonlinear refraction of the fabricated NP layers. The third-order nonlinear refractive index coefficients for Au and Ag are (-9.34 and -1.61) x 10(-11) cm(2) W-1 given lower n(2), in comparison with bilayer (Au and Ag) NPs at -1.24 x 10(-10) cm(2) W-1. The results show bilayer NPs have higher refractive index coefficients thus enhance the nonlinearity effects.