Unipolar pulse of an electromagnetic field with uniform motion of a charge in a vacuum

Progress in the generation of extremely short pulses of electromagnetic radiation makes the question of the properties of the limiting form of their shortening—unipolar pulses with a significant zero-frequency component of the spectrum, that is, the electric area of the pulse—relevant. Recently, it has been established that it is the electric area that determines the effectiveness of the impact of extremely short pulses on micro-objects. At the same time, unipolar pulses have a number of unusual properties, which makes some researchers doubt the possibility of their existence and propagation. Here, we show that a uniformly moving relativistic electric charge creates a short unipolar pulse of the electromagnetic field. Unipolarity is realized as well for transition radiation. We also present the unipolarity condition for a pair of charges—a dipole—and for a more general system of moving charges. This confirms the reality of unipolar electromagnetic pulses, which are promising for applications of extremely short pulses.