  In a famous paper where he introduces the A and B coefficients, Einstein
considered that atomic decays of excited atoms can be stimulated by light
waves. Here we consider that atomic decays can also be stimulated by atomic
waves. It is however necessary to change the Maxwell-Boltzmann statistics of
thermal equilibrium into Bose-Einstein statistics and to introduce a
coefficient C which complements the list of the coefficients introduced by
Einstein. Stimulated emission of light can be considered as the first step
towards the laser. Similarly, stimulated production of matter waves can be
considered as the basic phenomenon for an atom-laser. Most of the results that
we obtain here are not new. However, the method that we use remains very close
to elementary classical physics and emphasizes the symmetry between
electromagnetic and matter waves from various points of view.
