The nonlinear optical response of transparent silver/gold multi-metal layers

We report on the linear and nonlinear optical properties of Ag/Au multi-metal thin films and Fabry-Perot resonator cavities. The linear optical properties of these multi-metal layers, having different mass distributions and Ag/Au ratios with thicknesses around 15 nm, resemble those of electrically continuous metal layers. The optical losses introduced by interband transitions in the Au layers are reduced to achieve peak transmittances of 76 % around 550 nm. Using femtosecond-pulsed white-light continuum pump-probe experiments we show that the nonlinear optical response of such multi-metal layers is comparable to that of neat Au thin films. Low-finesse Fabry-Perot resonators fabricated with such multi-metal layers, combine the large NLO response of Au with a transmittance of 60% and a spectral bandwidth that covers the visible spectral range.