Quasiparticle properties in the superconducting state are masked by the superfluid and are not directly accessibleto infrared spectroscopy. We show how one can use a Kramers–Kronig transformation to separate the quasiparticlefrom superfluid response and extract intrinsic quasiparticle properties in the superconducting state. We alsoaddress the issue of a narrow quasiparticle peak observed in microwave measurements, and demonstrate how itcan be combined with infrared measurements to obtain a unified picture of electrodynamic properties of cupratesuperconductors.