Stimulated Emission of Radiation in a Single Mode for both Resonance and   Non-resonance for Various Initial Photon Distributions
  This paper reexamines the results of Cummings in which the quantum mechanical two-level-system (TLS) interacts with the electromagnetic field with various initial distributions and extends that work for both resonant and non-resonant to times large enough to display multiple photon echoes. The results presented here include the initial pure coherent state, the field whose initial density matrix is the Gaussian superposition of coherent states (blackbody radiation) and density matrices of the field represented by various combinations of mixed coherent and thermal states with and without squeezing This paper provides, in addition to the matrix elements to the various states, both the algebraic and graphical representation for the first order correlation function G=<E+E-> for resonance and non-resonance. It is found that in all case, the application of non-resonance leads to oscillations in the first order correlation which was thought only to apply for the coherent state even for the case of the pure thermal state. 
M. T. Tavis and F. W. Cummings
quant-ph