Threshold Effects on Heavy Quark Production in $\gamma\gamma$   Interactions
  The exchange of gluons between heavy quarks produced in $e^+e^-$ interactions results in an enhancement of their production near threshold. We study QCD threshold effects in $\gamma\gamma$ collisions. The results are relevant to heavy quark production by beamstrahlung and laser back-scattering in future linear collider experiments. Detailed predictions for top, bottom and charm production are presented. 
O.J.P. Eboli, M.C. Gonzalez-Garcia, F. Halzen, and S.F. Novaes