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Abstract

Polaritons can provide strong optical field enhancement allowing to boost
light-matter interaction. Here, we experimentally observe enhancement of
mid-infrared second-harmonic generation (SHG) using grating-coupled surface
phonon polaritons of the 6H-SiC surface. In our experiment, we measure the SHG
along the polariton dispersion by changing the incidence angle of the
excitation beam. We observe hybridization between the propagating surface
phonon polaritons and localized plasmon resonances in the gold grating,
evidenced by the modification of the polariton dispersion as we change the area
ratio of grating and substrate. Design options for engineering the
plasmon-phonon polariton hybridization are discussed. Overall, we find a rather
low yield of polariton-enhanced SHG in this geometry compared to prism-coupling
and nanostructures, and discuss possible origins.