  Current bounds from the polarization of the CMB predict the scale-invariant
gravitational wave (GW) background of inflation to be out of reach for upcoming
GW interferometers. This prospect dramatically changes if the inflaton is a
pseudoscalar, in which case its generic coupling to any abelian gauge field
provides a new source of GWs, directly related to the dynamics of inflation.
This opens up new ways of probing the scalar potential responsible for cosmic
inflation. Dividing inflation models into universality classes, we analyze the
possible observational signatures. One of the most promising scenarios is
Starobinsky inflation, which may lead to observational signatures both in
direct GW detection as well as in upcoming CMB detectors. In this case, the
complementarity between the CMB and direct GW detection, as well as the
possibility of a multi-frequency analysis with upcoming ground and space based
GW interferometers, may provide a first clue to the microphysics of inflation.
