Third harmonic generation (THG) as a function of infrared fundamental wavelength for gold nanoparticles over a gold film was measured. This figure shows the gold nanoparticle that is separated from ultraflat gold film by a self-assembled monolayer (SAM). (Credit: Levi Smith) See Hajisalem et al. Opt. Mater. Express 5, 2217-2224 (2015).