The high-energy expansion for extended targets developed previously is used to describe the problem of electron pair production by photons, a problem of interest in linear-collider design. The treatment is valid throughout the range of possible parameters, from the classical regime to the extreme quantum domain. The relation between this process and pair production in a constant external field is discussed.

• Received 19 May 1989

DOI:https://doi.org/10.1103/PhysRevD.40.2462