  Electron wavefunctions in twisted bilayer graphene may have a strong single
layer character or be intrinsically delocalized between layers, with their
nature often determined by how energetically close they are to the Dirac point.
In this paper, we demonstrate that in magnetic fields, optical absorption
(cyclotron resonance) spectra contain signatures which may be used to
distinguish the nature of these wavefunctions at low energies, as well as to
locate low energy critical points in the zero-field energy spectrum. Optical
absorption for two different configurations -- electric field parallel and
perpendicular to the bilayer -- are calculated, which are shown to have
different selection rules with respect to which states are connected by the
perturbation. Interlayer bias further distinguishes transitions involving
states of a single layer nature from those with support in both layers. For
doped systems, a sharp increase in intra-Landau level absorption occurs with
increasing field as the level passes through the zero-field saddle point
energy, where the states change character from single layer to bilayer.
