  The strength of the electromagnetic fields in the bunch collision at a linear
collider will have a significant effect, yielding large numbers of
beamstrahlung photons and associated coherent pair production. These effects
are limited in the proposed ILC beam parameters which limit the strength of the
bunch field to $\Upsilon_{\text{ave}}=0.27$. The CLIC 3 Tev design by
comparison has a $\Upsilon_{\text{ave}}=3.34$ yielding huge number of coherent
pairs. In terms of the precision physics programs of these proposed colliders
there is an imperative to investigate the effect of the strong bunch fields on
higher order processes. From the exact wavefunctions used in the calculation of
transition rates within the Furry interaction picture, and using appropriate
simplifications, a multiplicative factor to the coupling constants was
obtained. This indicates a significant variation to the transition rate near
threshold energies. Further studies are in progress to calculate the exact
effect on expected observables.
