Linear and third-order nonlinear optical responses of multilayeredAg:Si3N4 nanocomposites

Abstract

The linear and third-order nonlinear responses of tailoredSi3N4/Ag/Si3N4 trilayersand (Si3N4/Ag)n/Si3N4 multilayers grown by alternating ion-beam sputtering have been studied by combiningcomplementary characterization techniques such as transmission electron microscopy,spectroscopic ellipsometry and degenerate four-wave mixing. The linear optical responsedominated by the surface plasmon resonance of Ag nanoparticles has been measured overthe whole visible range while the third-order nonlinear susceptibility has beenprobed at the surface plasmon resonance wavelength. Due to the weak in-planeinteraction between Ag nanoparticles, the linear and nonlinear optical responses of theSi3N4/Ag/Si3N4 trilayers are mainly influenced by the size and shape of the nanoparticles. A maximum value of1.1 × 10−7 esu has been found at 635 nm for the effective third-order nonlinear susceptibility ofthe trilayer with the highest amount of silver. The linear optical response of the(Si3N4/Ag)n/Si3N4 multilayers is shown to be dominated by the surface plasmon resonance of isolated layers ofweakly interacting nanoparticles at wavelengths shorter than 600 nm whereas a contributiondue to vertical interactions has been shown for higher wavelengths. Below the verticalpercolation threshold, their nonlinear optical response at the surface plasmon resonancewavelength is similar to the one of an isolated assembly of nanoparticles, and the effectivethird-order nonlinear susceptibility is slightly increased by decreasing the thickness of theSi3N4 spacer.