Summary
The classical dipole interaction of a two-level atom with a monochromatic electromagnetic wave is considered. Both atomic energy levels are assumed to be unstable. The solution of the problem for a time-dependent Hamiltonian is obtained. The amplitudes and probabilities of transitions between the energy levels as well as the cross-sections of resonance absorption and induced emission are obtained explicitly. It is shown that in both stationary and nonstationary limits the instability of the lower level does not lead to differential cross-sections of induced emission larger than those obtained from the Breit-Wigner formula in the standard collision theory.