Surface lattice resonances in second-harmonic generation from metasurfaces.

We investigate the role of surface-lattice resonances (SLRs) in second-harmonic generation (SHG) from arrays of metal nanoparticles. The SLRs affect the generated signal when the sample is rotated away from normal incidence. The adjustment of the incident angle tunes the SLRs to the fundamental wavelength for SHG and improves the quality of the resonance for better resonance enhancement of SHG. Compared to normal incidence, an enhancement by a factor of 10 is observed. However, at certain incident angles, the enhancement is interrupted by diffraction anomalies, which redirect light into the substrate, increasing radiation damping and compromising the quality of the resonance.