  Coherent signal containing thermal noise is a mixed state of radiation. There
are two distinct classes of such states, a Gaussian state obtained by
Glauber-Lachs mixing and a non-Gaussian state obtained by the canonical
probabilistic mixing of thermal state and coherent state. Though both these
versions are noise-included signal states, the effect of noise is less
pronounced in the Glauber-Lachs version. Effects of these two distinct ways of
noise addition is considered in the context of atom-field interaction; in
particular, temporal evolution of population inversion and atom-field
entanglement are studied. Quantum features like the collapse-revivals in the
dynamics of population inversion and entanglement are diminished by the
presence of thermal noise. It is shown that the features lost due to the
presence of thermal noise are restored by the process of photon-addition.
