  A high energy linear e^+e^- collider (LC) can also be used as a Photon
Collider (PC), using Compton scattering of laser photons on the e^+/e^- beams.
The leading order cross-section for the production of heavy quarks, e^+e^- ->
e^+e^- Q(\bar{Q}) X, at high transverse momenta is calculated for both LC and
PC modes. The sensitivity of this process to the parton distribution
parametrizations of real photons, especially the gluon content, is tested for
both modes.
