期刊
ACS PHOTONICS
卷 4, 期 5, 页码 1048-1053出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsphotonics.7b00118
关键词
surface phonon polariton; Otto geometry; nonlinear optics; silicon carbide; nanophononics; infrared free-electron laser
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.
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