  We discuss upcoming opportunities with cosmic microwave background (CMB)
observations during the post-WMAP era. The curl-modes of CMB polarization probe
inflationary gravitational waves (IGWs). While a significant source of
confusion is expected from cosmic shear conversion of polarization related to
density perturbations, higher resolution observations of CMB anisotropies can
be used for a lensing reconstruction and to separate gravitational-wave
polarization signature from that of lensing. Separations based on current
lensing reconstruction techniques allow the possibility to probe inflationary
energy scales below 10^15 GeV in a range that includes grand unified theories.
The observational detection of primordial curl-modes is aided by rescattering
at late times during the reionized epoch with optical depth to electron
scattering at the level of 0.1 and above. An improved measurement of this
optical depth is useful to optimize experimental parameters of a post-WMAP
mission attempting to target the IGW background.
