Abstract <p>We discuss the generation of nonlinear harmonics by an intense dipole electromagnetic pulse in a vacuum in the presence of a constant magnetic field. Using Maxwell’s nonlinear equations, following from the Heisenberg–Euler Lagrangian in the one-loop approximation, expressions are derived for the electromagnetic field of the second harmonic generated in this case. It is shown that the second harmonic pulse in its spatial structure is a magnetic octupole pulse if the initial electromagnetic pulse is an electric- or magnetic-dipole pulse.</p>