  Bernal bilayer graphene exhibits a band gap that is tunable through the
infrared with an electric field. We show that sublattice odd commensurate
twisted bilayer graphene (C-TBG) exhibits a band gap that is tunable through
the terahertz with an electric field. We show that from the perspective of
terahertz optics the sublattice odd and even forms of C-TBG are "inflated"
versions of Bernal and AA stacked bilayer graphene respectively with energy
scales reduced by a factor of 110 for the 21.79 degree commensurate unit cell.
This lower energy scale is accompanied by a correspondingly smaller gate
voltage, which means that the strong-field regime is more easily accessible
than in the Bernal case. Finally, we show that the interlayer coherence energy
is a directly accessible experimental quantity through the position of a
power-law divergence in the optical conductivity.
