  We theoretically demonstrate that increase of absorption with constant gain
in laser systems can lead to onset of laser generation. This counter-intuitive
absorption induced lasing (AIL) is explained by emergence of additional lasing
modes created by an introduction of an absorbing medium with narrow linewidth.
We show that this effect is universal and can be encountered in simple
Fabry-Perot-like systems and doped spherical dielectric nanoresonators. The
predicted behavior is robust against frequency detuning between the gain and
absorbing medium.
