Abstract: We report an analytical and numerical study of the dynamics of electromagnetically induced atomic population gratings during collisions of a sequence of unipolar pulses of unusual temporal shape (rectangular and triangular) in a multilevel resonant medium. The possibility of forming dynamic microcavities with Bragg-like mirrors, the shape of which is different at each resonant transition of the medium, is demonstrated. A simple analytical description of such microresonators is proposed based on an approximate solution of the time-dependent Schrödinger equation when the amplitude of the exciting pulses is small. In the case of high-power pulses, when perturbation theory is not applicable, the results of numerical calculations show the disappearance of microcavities and the emergence of nonharmonic gratings with an increase in the number of collisions between pulses. The studied phenomena demonstrate a possibility of using unipolar pulses of an unusual shape for ultrafast control of the medium properties. © Allerton Press, Inc. 2024. ISSN 1068-3356, Bulletin of the Lebedev Physics Institute, 2024, Vol. 51, Suppl. 5, pp. S365–S373. Allerton Press, Inc., 2024. Russian Text The Author(s), 2024, published in Kvantovaya Elektronika, 2024, Vol. 54, No. 2, pp. 77–83.