  Mirrorless lasing has been a topic of particular interest for about a decade
due to promising new horizons for quantum science and applications. In this
work, we review first-principles theory that describes this phenomenon, and
discuss degenerate mirrorless lasing in a vapor of Rb atoms, the mechanisms of
amplification of light generated in the medium with population inversion
between magnetic sublevels within the $D_2$ line, and challenges associated
with experimental realization.
