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Description
Surface phonon polaritons (SPhPs) are quasiparticles resulting from the hybridisation of IR photons with transverse optical phonons. The extreme light confinement, the low losses due to the long phonon lifetimes and the high directionality that can result from low crystal symmetries are among the factors that have made phonon polaritons so attractive to the nanophotonics community in the last decade. In this contribution we propose two methods to characterise SPhPs. First, we show that spectroscopic ellipsometry can be combined with prism coupling to study the effect of SPhP excitation on the polarisation states of the reflected light. In addition, we report spectro-imaging in momentum space, which provides a fast and accurate dispersion mapping of SPhPs. As an outlook, we propose a combination of these two approaches - ellipsometry and momentum-space imaging - for an in-depth study of polariton polarisation states in low-symmetry van der Waals materials.
