  We investigate near-field infrared spectroscopy and superfluid polariton
imaging experiments on conventional and unconventional superconductors. Our
modeling shows that near-field spectroscopy can measure the magnitude of the
superconducting energy gap in Bardeen-Cooper-Schrieffer-like superconductors
with nanoscale spatial resolution. We demonstrate how the same technique can
measure the c-axis plasma frequency, and thus the c-axis superfluid density, of
layered unconventional superconductors with a similar spatial resolution. Our
modeling also shows that near-field techniques can image superfluid surface
mode interference patterns near physical and electronic boundaries. We describe
how these images can be used to extract the collective mode dispersion of
anisotropic superconductors with sub-diffractional spatial resolution.
