  We present infrared spectra (0.1-1 eV) of electrostatically gated bilayer
graphene as a function of doping and compare it with tight binding
calculations. All major spectral features corresponding to the expected
interband transitions are identified in the spectra: a strong peak due to
transitions between parallel split-off bands and two onset-like features due to
transitions between valence and conduction bands. A strong gate voltage
dependence of these structures and a significant electron-hole asymmetry is
observed that we use to extract several band parameters. Surprisingly, the
structures related to the gate-induced bandgap are much less pronounced in the
experiment than predicted by the tight binding model.
