  A time-domain approach is proposed for the propagation of ultrashort electro-
magnetic wave packets beyond the paraxial and the slowly-varying-envelope
approximations. An analytical method based on perturbation theory is used to
solve the wave equation in free space without resorting to Fourier trans-
forms. An exact solution is obtained in terms of successive temporal and
spatial derivatives of a monochromatic paraxial beam. The special case of a
radially polarized transverse magnetic wave packet is discussed.
