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We present a time-dependent study of a three-level ladder scheme interacting with two electromagnetic fields, utilizing a dressed-state approach. Analytical expressions for time-dependent populations and coherences are obtained under the secular approximation. These are found in good agreement with exact numerical solutions. It is found that the system exhibits gain both with and without inversion. The calculated temporal gain is found to be essentially larger than the steady-state gain. The frequency response of density matrix elements has been studied. Both normal and abnormal dispersion–absorption relations have been obtained.

A dressed-state study of lasing without population inversion from a three-level atom interacting with a bi-chromatic laser field in the ladder configuration is presented. In our model we allow the atom to be dressed by both of the coupling and probe fields. The system under consideration is explored both analytically and numerically within the steady-state regime. A parameter study is performed in which we explore the influence of the change of control parameters (Rabi frequencies and incoherent pump rates, etc) on the system behaviour. The parameter study also applies to situations where both coherent fields have comparable intensities. Expressions for steady-state populations and coherences are derived, from which the constraints on the system control parameters allowing gain or absorption of various types, are calculated. The system is demonstrated to possess gain without inversion (GWI), as well as regular gain with inversion, for the appropriate choice of system control parameters. Inversion without lasing (IWL) is also found. The dressed-state approach offers a different insight into the system dynamics in which Rabi oscillations and spectral features appear natural. We believe that the dressed-state approach provides a more adequate description of the system dynamics than that provided by the bare state basis.

Light induced absorption with population inversion and amplification without population inversion (LWI) in a coherently prepared closed three level Vtype system are investigated. This study is performed from the point of view of a two color dressed state basis. Both of these processes are possible due to atomic coherence and quantum interference contrary to simple intuitive predictions. Merely on physical basis, one would expect a complementary process to the amplification without inversion. We believe that absorption in the presence of population inversion found in the dressed state picture utilized in this study, constitutes such a process.Novel approximate analytic time dependent solutions, for coherences and populations are obtained, and are compared with full numerical solutions exhibiting excellent agreement. Steady state quantities are also calculated, and the conditions under which the system exhibits absorption and gain with and without inversion, in the dressed state representation are derived. It is found that for a weak probe laser field absorption with inversion and amplification without inversion may occur, for a range of system parameters. *shuker@bgumail.bgu.ac.ilRecently there has been tremendous interest in the study of light amplification and lasing without the requirement of population inversion (LWI), potentially capable of extending the range of laser devices to spectral region in which, for various reasons, population inversion is difficult to achieve. These spectral regions include UV which can be obtained from atomic vapor, and mid-to-far infrared, obtained by interssubband transitions in quantum wells. Many models for LWI have been proposed, mostly three and four level schemes, in Λ and V configurations. The dependence of optical gain on system parameters has also been investigated [1-17].The key mechanism, which is common to most of the proposed schemes, is the utilization of external coherent fields, that induce quantum coherence and interference in multilevel systems.An exception of LWI without the use of coherent fields was also reported [9]. In particular it was shown that if atomic coherence between certain atomic states is established , different absorption processes may interfere destructively leading to the reduction or even the cancellation of absorption [7,13]. At the same time stimulated emission may remain intact, leading to the possibility of gain even if only a small fraction of the population is in the excited state.Experimental observations of inversionless gain and lasing without inversion have been reported by several groups [18][19][20][21]. Inversionless lasers have been shown to have unique properties such as non classical photon statistics and substantially narrow spectral features [22,23]. In a recent paper, Y. Zhu [12] analyzed the transient and steady state properties of light amplification without population inversion in a closed three level V type system in the bare state basis.Steady state dressed state populations were also calculated, in the limit of strong...

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