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Acta Optica Sinica

Four-level atomic system resonantly pumped by double-wave fields

Uo G

Published Jan 1, 1988• 0 citations
OpenAlex

Abstract

A four-level atomic system interacting with two laser fields and one probe field has been transformed into a four-level Dressed-Atom System interacting with a weak probe absorption field by means of the Dressed-Atom states. By using perturbation theory to solve the density matrix equations in Dressed-Atom representation, the analytic expressions for absorption spectrum are obtained. The properties of absorption spectrum are discussed in detail. Finally, the induced electric dipole moment between the atomic levels and its relation with the absorption spectrum are deduced.

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Acta Physica Sinica•Jan 1, 2010•1 citation
A four-level atomic system interacting with two laser fields and one probe field has been transformed into a four-level Dressed-Atom System interacting with a weak probe absorption field by means of the Dressed-Atom states. By using perturbation theory to solve the density matrix equations in Dressed-Atom representation, the analytic expressions for absorption spectrum are obtained. The properties of absorption spectrum are discussed in detail. Finally, the induced electric dipole moment between the atomic levels and its relation with the absorption spectrum are deduced.
Abstract The absorption features of a probe field propagating through a four-level N-type atomic system in the presence of two coherent radiation fields is studied analytically by using a density matrix formulation. The system has two ground levels and two excited levels. A weak probe laser couples the upper ground level to the lower excited level whereas a strong control field connects the lower ground level to the lower excited level. The coupling field acts between the upper ground level and the upper excited level. The transition parameters of the 87 Rb D 1 line have been used to simulate the probe response. The simulated probe absorption shows a gain-like structure depending on the relative field intensities. The spectral features of the probe response exhibit substantial differences under thermal averaging as compared to a Doppler-free condition. The splitting of simulated probe absorption can be explained by the dressed state model. Electromagnetically induced absorption (EIA) is observed in the simulated probe response curve when the spontaneous decay of the population from the uppermost excited state to the lower ground state is absent.
We examine the absorption of a weak probe beam by a laser driven V-type atom with a pair of closely lying excited levels, where both the driving and probe lasers interact simultaneously with the two transitions. The effects of quantum interference among decay channels on the absorption spectra are also investigated. We introduce dipole moments in the dressed-state representation and the Hamiltonian in terms of the dressed states describing the interaction between the probe and the atom. In the degenerate case, features similar to that of a driven two-level atomic system are found due to some dark transitions in the spontaneous emission and the fact that the probe beam only detects certain transitions. In the nondegenerate case, the absorption spectrum is strongly influenced by the degree of quantum interference, resulting in different line shapes for emission peaks, absorption peaks, and dispersionlike profiles. The effect of probe polarization on the absorption spectrum is also investigated.
Using matrix theory,the absorption and dispersion properties of a lamda-type four-level system driven by two coherent fields are investigated.The result obtained by means of numerical method indicates that by adjusting the intensity of Rabi frequencies of the coherent field in the steady state,double or single electromagnetically induced transparency(EIT) can appear explicitly in this system.And the explanations of these phenomena are given by using the dressed states.In the double electromagnetically induced transparency,the location of transparent windows can be manipulated by controlling the detuning of the driving field.Additionally,it is also found that the medium shows a large refractive index at each transparency window,and the group velocity of the probe laser can be enhanced.
We have investigated the dispersive properties of excited-doublet four-level atoms interacting with a weak probe field and an intense coupling laser field. We have derived an analytical expression of the dispersion relation for a general excited-doublet four-level atomic system subject to a one-photon detuning. The numerical results demonstrate that for a typical rubidium Dl line configuration, due to the unequal dipole moments for the transitions of each ground state to double excited states, generally there exists no exact dark state in the system. Close to the two-photon resonance, the probe light can be absorbed or gained and propagate in the so-called superluminal form. This system may be used as an optical switch.
Using density matrix eqution, the absorption and dispersion properties of a A-type four-level system driven by coherent fields are investigated. The result obtained by means of numerical method indicates that by adjusting the intensity of Rabi frequencies of the coherent field in the steady state, three, double or single electromagnetically induced transparency (EIT) can appear explicitly in this system. And the explanations of these phenomena are given by using the dressed states. In the three EIT, the location of transparent windows can be manipulated by controlling the detuning of the driving field. What's more, it is also found that the medium shows a large refractive index at each transparency window, and the group velocity of the probe laser can be enhanced.
In this paper, we have calculated the absorption of the probing field in a N-type four-level atomic system with three dipole transitions using density matrix equation. The results indicate that the absorption or amplification of the probing field depends on the Rabi phases of the control field and signal field under introducing laser field Rabi phase, and the absorption or amplification periodically changes with the Rabi phases of the control field and the signal field at a period of 2π. The Rabi phase change of the probe field has no effect on the absorption. In addition, the effect of the signal field Rabi phase on absorption is the same as that of the control field Rabi phase on absorption. Rabi phase has an effect mainly on atomic coherence but little on atomic population.