  We present the first measurements of cyclotron resonance of electrons and
holes in bilayer graphene. In magnetic fields up to B = 18 T we observe four
distinct intraband transitions in both the conduction and valence bands. The
transition energies are roughly linear in B between the lowest Landau levels,
whereas they follow \sqrt{B} for the higher transitions. This highly unusual
behavior represents a change from a parabolic to a linear energy dispersion.
The density of states derived from our data generally agrees with the existing
lowest order tight binding calculation for bilayer graphene. However in
comparing data to theory, a single set of fitting parameters fails to describe
the experimental results.
