Second harmonic generation spectroscopy on second harmonic resonant plasmonic metamaterials

The field enhancement resulting from the resonant excitation of plasmonic modes in metallic nanostructures allows to amplify nonlinear processes such as second harmonic generation in plasmonic metamaterials. Thus far, nonlinear experiments with metallic nanostructures relied on the resonant enhancement of the pump light by a plasmonic mode. Here, we report on second harmonic generation spectroscopy on plasmonic metamaterials that only exhibit a plasmonic resonance at twice the pump frequency. We also observe in this case a strong enhancement of the second harmonic generation signal, even though the driving pump field is not resonantly enhanced. The experimental data can be explained in terms of the anharmonic oscillator model and classical symmetry selection rules applied to nonlinear metamaterials. Our findings pave the way for further optimizations of the nonlinear response of plasmonic metamaterials. (C) 2015 Optical Society of America