Threshold effects on heavy quark production in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>γ</mml:mi><mml:mi>γ</mml:mi></mml:math>interactions

The exchange of gluons between heavy quarks produced in ${e}^{+}{e}^{\ensuremath{-}}$ interactions results in an enhancement of their production near threshold. We study QCD threshold effects in $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions. The results are relevant to heavy quark production by beamstrahlung and laser backscattering in future linear collider experiments. Detailed predictions for top-, bottom-, and charm-quark production are presented.