Nikolai Christian Passler, Ilya Razdolski, Sandy Gewinner, Wieland Schöllkopf, Martin Wolf, and Alexander Paarmann:
ACS Photonics. 4 (5), 1048-1053 (2017), pp.6;
Mid-infrared nanophotonics can be realized using subdiffractional light localization and field enhancement with surface phonon polaritons in polar dielectric materials. We experimentally demonstrate second-harmonic generation due to the optical field enhancement from critically coupled surface phonon polaritons at the 6H-SiC–air interface, employing an infrared free-electron laser for intense, tunable, and narrowband mid-infrared excitation. Critical coupling to the surface polaritons is achieved using a prism in the Otto geometry with adjustable width of the air gap, providing a contact-free access to the polariton dispersion with full control over the excitation conditions. The calculated reflectivity and second-harmonic spectra reproduce the complete experimental data set with high accuracy, allowing for a quantification of the optical field enhancement. We also reveal the mechanism for low out-coupling efficiency of the second-harmonic light in the Otto geometry. Perspectives on surface phonon polariton-based nonlinear sensing and nonlinear waveguide coupling are discussed.
The original publication is available by link DOI: 10.1021/acsphotonics.7b00118