Single top production in e+e-, e-e-, γe and γγ collisions

Single top quark cross section evaluations for the complete sets of tree-level diagrams in the e(+)e(-), e(-)e(-), gammae and gamma gamma modes of the next linear collider with unpolarized and polarized beams are performed within the standard model and beyond. From a comparison of all possibilities we conclude that the process gamma +e ((L)) over bar -->c(-)t (b) over bar is extremely favored due to large cross sections, there being no t (t) over bar background, the high degrees of beam polarization, and the exceptional sensitivities to V-tb and anomalous Wtb couplings. Similar reasons favor the process e(-)e(-)--> e-nu (e)(t) over barb for probing top quark properties despite a considerably lower cross section. Less favorable are processes like e(+)e(-), gamma gamma --> e(-)nu (e)t (b) over bar. Three processes were chosen to probe their sensitivities to anomalous Wtb couplings, with best bounds found for gamma +e(L)(-) --> e(-)t (b) over bar and e(R)(+)e(R)(-) -->e-nu (e)t (b) over bar.