  We report on the detailed analysis of the infrared (IR) conductivity of two
prototypical high-$T_{c}$ systems YBa$_{2}$Cu$_{3}$O$_{y}$ and
La$_{2-x}$Sr$%_{x}$CuO$_{4}$ throughout the complex phase diagram of these
compounds. Our focus in this work is to thoroughly document the electromagnetic
response of the nodal metal state which is initiated with only few holes doped
in parent antiferromagnetic systems and extends up to the pseudogap boundary in
the phase diagram. The key signature of the nodal metal is the two-component
conductivity: the Drude mode at low energies followed by a resonance in mid-IR.
The Drude component can be attributed to the response of coherent
quasiparticles residing on the Fermi arcs detected in photoemission
experiments. The microscopic origin of the mid-IR band is yet to be understood.
A combination of transport and IR data uncovers fingerprints of the Fermi
liquid behavior in the response of the nodal metal. The comprehensive nature of
the data sets presented in this work allows us to critically re-evaluate common
approaches to the interpretation of the optical data. Specifically we
re-examine the role of magnetic excitations in generating electronic self
energy effects through the analysis of the IR data in high magnetic field.
