Recently, interest in extremely short unipolar electromagnetic pulses with non-harmonic shape (e.g. rectangular or triangular) is rising. Such pulses do not contain a carrier frequency and have an ultra-wide spectrum. Compared to conventional harmonic multicycle pulses, they are faster and more efficient in controlling the properties of quantum systems, which allows, in the future, for faster data transmission and processing. With coherent interaction of extremely short light pulses with a medium, formation and ultrafast control of population difference gratings and polarization structures are possible when the pulses both overlap and do not overlap in the medium. In this work, based on the numerical solution of Maxwell–Bloch equations, we demonstrate possible creation of a dynamic “microcavity” as a burst of population difference, arising from the collision of rectangular unipolar 1-femtosecond pulses of self-induced transparency in a two-level resonant medium. Potential to control the microcavities parameters (changing the depth, turning it on, erasing it, etc.) is demonstrated.