  The absorption of heavily doped graphene in the terahertz (THz) and
mid-infrared (MIR) spectral regions is considered taking into account both the
elastic scattering due to finite-range disorder and the variations of
concentration due to long-range disorder. Interplay between intra- and
interband transitions is analyzed for the high-frequency regime of response,
near the Pauli blocking threshold. The gate voltage and temperature
dependencies of the absorption efficiency are calculated. It is demonstrated
that for typical parameters, the smearing of the interband absorption edge is
determined by a unscreened part of long-range disorder while the intraband
absorption is determined by finite-range scattering. The latter yields the
spectral dependencies which deviate from those following from the Drude
formula. The obtained dependencies are in good agreement with recent
experimental results. The comparison of the results of our calculations with
the experimental data provides a possibility to extract the disorder
characteristics.
