  Inelastic scattering of visible light (Raman effect) offers a window into
properties of correlated metals such as spin, electron and lattice dynamics as
well as their mutual interactions. In this review we focus on electronic and
spin excitations in Fe-based pnictides and chalcogenides in particular, but not
exclusively superconductors. After a general introduction to the basic theory
including the selection rules for the various scattering processes we provide
an overview over the major results. In the superconducting state below the
transition temperature Tc the pair-breaking effect can be observed, and the
energy gap can be derived. The energies can be associated with the gaps and
their anisotropy on the electron and hole bands. In spite of the similarities
of the overall band structures the results are strongly dependent on the family
and may even change qualitatively within one family. In some of the compounds
strong collective modes appear below Tc. In Ba1-xKxFe2As2, which has the most
isotropic gap of all Fe-based superconductors, there are indications that these
modes are exciton-like states appearing in the presence of a hierarchy of
pairing tendencies. The strong in-gap modes observed in Co-doped NaFeAs are
interpreted in terms of quadrupolar orbital excitations which become undamped
in the superconducting state. The doping dependence of the scattering intensity
in Ba(Fe1-xCox)2As2 is associated with a nematic resonance above a quantum
critical point and interpreted in terms of a critical enhancement at the
maximal Tc. In the normal state the response from particle-hole excitations
reflects the resistivity. In addition, there are contributions from presumably
critical fluctuations in the energy range of kBT which can be compared to the
elastic properties. Currently it is not settled whether the fluctuations
observed by light scattering are related to spin or charge.
