Linear and nonlinear optical study of metal nanoparticle monolayers

The optical properties of single layers of metallic Ga nanoparticles have been explored experimentally with linear and nonlinear techniques. The samples were fabricated by evaporation-condensation in ultrahigh vacuum, exploiting the partial wetting of Ga with respect to the underlying SiOx matrix. The net optical response of such self-assembled liquid Ga nanoparticles was determined using cw optical methods as well as pulsed laser excitation. Second harmonic generation was observed in transmission and reflection geometry using femtosecond laser pulses. The second-harmonic signal dependence on particle size is presented and discussed. While measuring the nonlinear response vs. temperature, a remarkable melting-induced enhancement of the second harmonic generated signal was measured at the solid-to-liquid phase transition of the embedded Ga nanoparticles.