Infrared near-field microscopy allows to study the propagation of surface waves in the infrared spectral regime. Amplitude and phase resolved near-field images reveal local interference effects or enable the determination of the complex wave vector of surface waves. Surface waves can be excited in the mid-infrared spectral regime by e.g. metal structures on Silicon Carbide (SiC) crystals (propagating Surface Phonon Polaritons, SPhP).
The topography image shows a circular structure used to excite SPhPs. The SPhPs propagate normal to the edge of the metal film and the curved structure leads to a focusing effect of the waves. The near-field amplitude image clearly reveals a locally enhanced signal about 40µm away from the structure. Note that the metal structure is illuminated by a plane wave (used to excite the SPhPs) which interferes with the field of the surface waves. The images demonstrate that infrared near-field microscopy can be used for amplitude and phase resolved studies of e.g. spoof plasmons with tailored optical properties in detail.