Phonon-polariton Bragg generation at the surface of silicon carbide

Phonon polaritons are known to emerge at the surfaces of solids under IR irradiation at frequencies close to the optical phonon resonance. Metal, patterned on the top of the polariton-active surface, locally blocks the excitation of the surface waves due to plasmonic screening and can be used for the design of wave patterns. We excite the polaritonic waves at the surface of SiC under the irradiation of a CO$_2$ laser ($\lambda\sim10$ $\mu$m) and visualize them using apertureless near-field interference scanning probe microscopy. From the near-field scans in the vicinity of the gold film periodical strip structures, we identify the Bragg scattering (diffraction) outside the lattice with the contribution from separate strips coherently summed up, provided that the wavelength matching condition is fulfilled. The observed phenomena agree with the wavefield calculations. Our observations demonstrate the potential of metal-patterned silicon carbide for the fabrication of on-chip polaritonic IR circuits.