The steady-state populalions and Ihe absorption spectrum of a V-type theree-level atom driven by a strong coherent lield lind a weak slochastic one simultaneously ale ibvestigated. The populaltion inversion in bare-sale and dressed-state bases Can happen significantly due to the effect of tile stochastic field. A relation between tile level gap of both atomic exciled slates and the Rabi frequency is found to decide in which excited state the population is lalger than in another one for the same frequency detuning δ between the coherent and the stochastic fields. The line profiles of the absorption spectrumare strognly dependent on the frquency detuing δ, Different lineshapes such as a sharp emission peak (gain). an absorption peak or a dispersion-like peak can be exhibited al the line centre for differentδ. Asymmetrical spectral features and line narrowing can be reached by adjusling δ and the Rabi frequency. Plobe gain in sidebands can occur due to the unbalanced populalion distribuitn in dressed states.

We investigate the effect of the dipole-dipole interaction on the dynamic properties and the atomic coherent trapping of a two-identical atom system in the presence of a laser field by means of quantum electrodynamics theory, The influence of the dipole-dipole interaction on the collapses and revivats of the atomic population is revealed. The conditions of the atomic eoherent trapping are given. A way to measure optically the coupling strength between the atoms is pointed out. Wc also show that the cffect of the dipole-dipole interaction may be screened duc to the coherent field in certain atomic superposition states.

In this paper, we have investigated the time evolution of |he phase operator of the radiation field in the Jaynes-Cummings model with and without tfie rotating-wave approximation, making use of the phase formalism of Barnett and Pegg [J. Mod. Opt. 56, 7 (1989); Phys. Rev. A 39, 1665 (1989)]. We verify by an analytical method that the atomic Rabi oscillation leads to phase dissipation of the radiation field, and also that the effect of the virtual-photon field can exhibit quantum fluctuations in the atomfield-coupling system and lead to a Frequency shift of the radiation field.

In this paper, we have investigated the influence of the cvunler-rotating terms on the squeezing of light in the two photon layaes-Cummings mcodel by means of the nonrelativistic QED. We verified that the effect af the virtual-photon field increases the squeezing. The relations between the degree of squeezing and the frequency of field, the mean photon number, and the atom-field coupling constant have alsp been analyzed.

We have studied the time evolutiort of the phase operators of the radiation field in the system contain-ing a V-type three-level atom interaeting with the bimodal field by means of the phase formalism given by Pegg and Borneo [J. Me.d. Opt. 36, 7 (1998); Phys: Rev. A 39, 1665 (1989)]. That the atomic coherent trapping will happen in an appropriate initial state of the system has also been verified.