The ambiguity of representing the density matrix of laser light by coherent states or by the number states is “inherited” from a similar ambiguity in the description of lasing mechanisms. Atomic excitation by electron impact is analyzed, and it is concluded that in normal discharge lasers, the lasing atoms become energetically entangled with the electrons and no mean dipoles are excited.

• Received 20 February 1998

DOI:https://doi.org/10.1103/PhysRevA.58.4247