Recently, the possibility of obtaining non-harmonic unipolar electromagnetic pulses with a specific electric field strength’s dependence on time (e.g. a rectangular pulse) has been actively discussed in optics. Unipolar pulses have a nonzero electric area and a wide spectrum: from zero frequency up to the visible region. This could open up wide application of such pulses, for example, for faster and more efficient control of the quantum systems’ properties with a high temporal resolution compared to conventional bipolar multicycle pulses. In this paper, based on an approximate solution of the time dependent Schrödinger equation and a numerical solution of the equation system for the density matrix, we show the possibility of creating electromagnetically induced population density gratings in an atomic medium using a pair of unipolar rectangular attosecond light pulses that do not overlap in the medium. The formation of such gratings can be explained on the basis of the concept of ‘interference’ of electric pulse areas, recently introduced into optics.

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Photons have zero rest mass and always travel at the speed of light in a vacuum, but have no dipole moment. Atoms and molecules, which may have a constant or variable dipole moment, have mass and therefore cannot move at or above the speed of light. As a result, the radiation from such systems moving at the velocity of light was not considered. However, it is possible to create many artificial objects (light spots, effective charges, current pulses, etc.) that can travel at the speed of light and even exceed it. In this case, they become a source of electromagnetic radiation. In this work, the radiation of a solitary polarization pulse that travels at the speed of light and has a variable or constant amplitude is discussed. It is shown that if the amplitude does not change, then such an object does not radiate outward, i.e., the field emitted by it remains completely localized inside the moving polarization pulse. If the amplitude changes over time, then it begins to radiate backwards. In this case, unipolar pulses of an unusual shape, such as a rectangular one, can be obtained.

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