Induced radiation

Bohr, Einstein, Plank and other works on induced radiation of atoms in excited state are analysed. Large importance of the Einstein conclusion that interaction of atoms with light quanta lead both to Boltzmann distribution energy levels and to Maxwellian velocity distribution is marked. Achievements in obtianing inverse populated states, and also the methods permitting to obtain inverse population in pulsed and continious regimes, are commented. The examples illustrating the possibilities of quantum electrodynamics are presetned. It is stressed that the fundamental Einsteins contribution in physics of radiation interactions with quantum systems nowadays continue to affect greatly the development of study in this field