Strong nonlinear optical response from ZnO by coupled and lattice-matched nanoantennas

We show the effective generation of second harmonic generated light in thin zinc oxide (ZnO) films by using double-resonant plasmonic nanoantennas. The designed structure consists of three gold rods with two localized surface plasmon resonances at omega and 2 omega. Two of the nanoantennas are designed to be resonant for the fundamental frequency omega in order to provide a strong localization of light. The third antenna lies in between the two fundamental antennas separated by a small gap (approximate to 30 nm). Due to a strong overlap between the second harmonic resonance at 2 omega and the fundamental resonance, the overall far-field radiation is significantly increased. Second harmonic generation spectroscopy measurements show an enhancement by a factor of nine compared to the emission from single dipole rods. Additionally, by optimizing the lattice constant for the nanoantenna arrays, the overall second harmonic response from the ZnO was significantly increased by a factor as large as 70, which is a great improvement for comparable plasmonic nanoantennas on thin zinc oxide. Published under license by AIP Publishing.