  Quasiparticle properties in the superconducting state are masked by the
superfluid and are not directly accessible to infrared spectroscopy. We show
how one can use a Kramers--Kronig transformation to separate the quasiparticle
from superfluid response and extract intrinsic quasiparticle properties in the
superconducting state. We also address the issue of a narrow quasiparticle peak
observed in microwave measurements, and demonstrate how it can be combined with
infrared measurements to obtain unified picture of electrodynamic properties of
cuprate superconductors.
