Elementary processes of lengthening of spontaneous radiation trains

Spontaneous and stimulated emission from atoms in a free one-dimensional space is considered from the quantum-mechanical point of view. The resolvent method is used to calculate the field density matrix, average electric field, and electromagnetic field energy density for a spontaneously emitting atom. For an atom emitting in the field of another atom, calculations are made of the electric field of the spontaneous and stimulated radiation. It is shown how the coherence length and coherence time of the spontaneous radiation increase. The application of these results in laser theory to explain the formation of a radiation mode structure and consequent appearance of coherent radiation is discussed.