Fig. 3: Otto-type prism coupling measurement for the experimental observation of LPs.

a Otto-type prism coupling configuration. b Azimuthal dispersion extracted from experimental data and c transfer matrix simulations for calcite (100), with the optical axis tilted by \(\theta={23.3}^{^\circ }\) with respect to the interface (as displayed in a). These simulations were performed by taking into account the presence of a Thallium Bromoiodide (KRS5) prism when setting up the material system and calculating for each configuration the corresponding reflectance spectrum. The in-plane momentum is fixed at \(\frac{{q}_{{{{{{\rm{r}}}}}}}}{{k}_{0}}=1.07\). d experimental and e simulated polariton resonance frequency map. The polariton resonance frequencies in the simulated maps are derived from the imaginary part of the reflection coefficients for p-polarized light \({\mathfrak{I}}({r}_{{{{{{\rm{pp}}}}}}})\). f Simulated (lines) and experimental (circles) IFCs at multiple frequencies, demonstrating the lenticular dispersion of LPs. g Experimental and h simulated LP Q-factors as a function of in-plane momentum. i Simulated (lines) and experimental (circles) LP Q-factors along the IFCs at multiple frequencies. j Experimental geometry for LP dispersion measurement inside the FSLC. k, l Experimental isofrequency reflectance maps and m, n respective simulations for (100) calcite. The green solid lines show the analytical LP dispersion using Eq. (1). Note that we observe a spectral offset of ~\(5\,{{{{{{\rm{cm}}}}}}}^{-1}\) between experiment and simulations consistently for all measurements.